Right on schedule: Physicists use modeling to forecast a black hole's feeding patterns with precision

The dramatic dimming of a light source ~ 860 million light-years away from Earth confirms the accuracy of a detailed model developed by a team of astrophysicists, including Syracuse University Professor Eric Coughlin.

Powerful telescopes like NASA's Hubble, James Webb, and Chandra X-ray Observatory provide scientists a window into deep space to probe the physics of black holes. While one might wonder how you can "see" a black hole, which famously absorbs all light, this is made possible by tidal disruption events (TDEs) -- where a star is destroyed by a supermassive black hole and can fuel a "luminous accretion flare." With luminosities thousands of billions of times brighter than the Sun, accretion events enable astrophysicists to study supermassive black holes (SMBHs) at cosmological distances.

TDEs occur when a star is violently ripped apart by a black hole's immense gravitational field. As the star is shredded, its remnants are transformed into a stream of debris that rains back down onto the black hole to form a very hot, very bright disk of material swirling around the black hole, called an accretion disc. Scientists can study these to make direct observations of TDEs, and compare those to theoretical models to relate observations to physical properties of disrupted stars and their disrupting black holes.

A team of physicists from Syracuse University, MIT and the Space Telescope Science Institute used detailed modeling to predict the brightening and dimming of AT2018fyk, which is a repeating partial TDE, meaning the high-density core of the star survived the gravitational interaction with the SMBH, allowing it to orbit the black hole and be shredded more than once. The model predicted that AT2018fyk would "dim" in August 2023, a forecast which was confirmed when the source went dark last summer, providing evidence that their model delivers a new way to probe the physics of black holes. Their results were published in The Astrophysical Journal Letters.

A High Energy Source

Thanks to incredibly detailed extragalactic surveys, scientists are monitoring more coming and going light sources than ever before. Surveys pan entire hemispheres in search of sudden brightening or dimming of sources, which tells researchers that something has changed. Unlike the telescope in your living room that can only focus visible light, telescopes such as Chandra can detect light sources in what's referred to as the X-ray spectrum emitted from material that is millions of degrees in temperature.

Visible light and X-rays are both forms of electromagnetic radiation, but X-rays have shorter wavelengths and more energy. Similar to the way in which your stove becomes "red hot" after you turn it on, the gas comprising a disc "glows" at different temperatures, with the hottest material closest to the black hole. However, instead of radiating its energy at optical wavelengths visible to the eye, the hottest gas in an accretion disc emits in the X-ray spectrum. These are the same X-rays used by doctors to image your bones and that can pass through soft tissue, and because of this relative transparency, the detectors used by NASA X-ray telescopes are specifically designed to detect this high-energy radiation.'

A Repeat Performance

In January 2023, a team of physicists, including Eric Coughlin, a professor at Syracuse University's Department of Physics, Dheeraj R. "DJ" Pasham, a research scientist at MIT, and Thomas Wevers, a Fellow at the Space Telescope Science Institute, published a paper in The Astrophysical Journal Letters that proposed a detailed model for a repeating partial TDE. Their results were the first to map a star's surprising return orbit about a supermassive black hole -- revealing new information about one of the cosmos' most extreme environments.

The team based their study on a TDE known as AT2018fyk (AT stands for "Astrophysical Transient"), where a star was proposed to be captured by a SMBH through an exchange process known as "Hills capture." Originally part of a binary system (two stars that orbit one another under their mutual gravitational attraction), one of the stars was hypothesized to have been captured by the gravitational field of the black hole and the other (non-captured) star was ejected from the center of the galaxy at speeds comparable to ~ 1000 km/s.

Once bound to the SMBH, the star powering the emission from AT2018fyk has been repeatedly stripped of its outer envelope each time it passes through its point of closest approach with the black hole. The stripped outer layers of the star form the bright accretion disk, which researchers can study using X-Ray and Ultraviolet /Optical telescopes that observe light from distant galaxies.

While TDEs are usually "once-and-done" because the extreme gravitational field of the SMBH destroys the star, meaning that the SMBH fades back into darkness following the accretion flare, AT2018fyk offered the unique opportunity to probe a repeating partial TDE.

The research team has used a trio of telescopes to make the initial and follow-up detections: Swift and Chandra, both operated by NASA, and XMM-Newton, which is a European mission. First observed in 2018, AT2018fyk is ~ 870 million light years away, meaning that because of the time it takes light to travel, it happened in "real time" ~ 870 million years ago.

The team used detailed modeling to forecast that the light source would abruptly disappear around August 2023 and brighten again when the freshly stripped material accretes onto the black hole in 2025.

Model Validation

Confirming the accuracy of their model, the team reported an X-ray drop in flux over a span of two months, starting on August 14, 2023. This sudden change can be interpreted as the second emission shutoff.

"The observed emission shutoff shows that our model and assumptions are viable, and suggests that we are really seeing a star being slowly devoured by a distant and very massive black hole," says Coughlin. "In our paper last year, we used constraints from the initial outburst, dimming and rebrightening to predict that AT2018fyk should display a sudden and rapid dimming in August of 2023, if the star survived the second encounter that fueled the second brightening."

The fact that the system displayed this predicted shutoff therefore implies several distinctions about the star and the black hole:

• the star survived its second encounter with the black hole;
• the rate of return of stripped debris to the black hole is tightly coupled to the brightness of AT2018fyk;
• and the orbital period of the star about the black hole is ~ 1300 days, or about 3.5 years.

The second cutoff implies that another rebrightening should happen between May and August of 2025, and if the star survived the second encounter, a third shutoff is predicted to occur between January and July of 2027.

As for whether we can count on seeing a rebrightening in 2025, Coughlin says the detection of a second cutoff implies that the star has had more mass freshly stripped, which should return to the black hole to produce a third brightening.

"The only uncertainty is in the peak of the emission," he says. "The second re-brightened peak was considerably dimmer than the first, and it is, unfortunately, possible that the third outburst will be dimmer still. This is the only thing that would limit the detectability of this third outburst."

Coughlin notes that this model signifies an exciting new way to study the incredibly rare occurrences of repeating partial TDEs, which are believed to take place once every million years in a given galaxy. To date, he says scientists have encountered only four to five systems that display this behavior.

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Exoplanet-hunting telescope to begin search for another Earth in 2026

Europe's next big space mission -- a telescope that will hunt for Earth-like rocky planets outside of our solar system -- is on course to launch at the end of 2026.

PLATO, or PLAnetary Transits and Oscillations of stars, is being built to find nearby potentially habitable worlds around Sun-like stars that we can examine in detail.

The space telescope will blast into orbit on Europe's new rocket, Ariane-6, which made its maiden flight last week after being developed at a cost of €4billion (£3.4billion).

Dr David Brown, of the University of Warwick, is giving an update on the mission at the Royal Astronomical Society's National Astronomy Meeting at the University of Hull this week.

"PLATO's goal is to search for exoplanets around stars similar to the Sun and at orbital periods long enough for them to be in the habitable zone," he said.

"One of the main mission objectives is to find another Earth-Sun equivalent pair, but it is also designed to carefully and precisely characterise the exoplanets that it finds (i.e. work out their masses, radii, and bulk density)."

PLATO isn't just an exoplanet hunter, however. It is also a stellar science mission.

As well as searching for exoplanets it will study the stars using a range of techniques including asteroseismology (measuring the vibrations and oscillations of stars) to work out their masses, radii, and ages.

Unlike most space telescopes, PLATO has multiple cameras -- including a UK-named one called ArthurEddington, after the famous astronomer and physicist who won the Royal Astronomical Society's Gold Medal in 1924.

It has 24 'Normal' cameras (N-CAMs) and 2 'Fast' cameras (F-CAMs). The N-CAMs are arranged into four groups of six cameras, with the cameras in each group pointing in the same direction but the groups slightly offset.

This gives PLATO a very large field of view, improved scientific performance, redundancy against failures, and a built-in way to identify 'false positive' signals that might mimic an exoplanet transit, Dr Brown explained.

"The planned observing strategy is to stare at two patches of sky, one in the North and one in the South, for two years each," he added.

"The Southern patch of sky has been chosen, while the Northern patch won't be confirmed for another few years."

Several of the spacecraft's components have finished their manufacturing programmes and are close to completing their calibration tests. This includes the UK-provided Front-End Electronics (FEE) for the N-CAMs.

Built by the Mullard Space Science Laboratory of University College London, these operate the cameras, digitise the images, and transfer them to the onboard data processing.

Ten of the final cameras have been built and tested and the first of these was mounted onto the optical bench -- the surface which keeps all cameras pointed in the right direction -- earlier this year.

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Exoplanets true to size

A star's magnetic field must be considered in order to correctly determine the characteristics of their exoplanets from observations by space telescopes such as Kepler, James Webb, or PLATO. This is demonstrated by new model calculations presented today in the journal Nature Astronomy by a research group led by the Max Planck Institute for Solar System Research (MPS) in Germany. The researchers show that the distribution of the star's brightness over its disk depends on the star's level of magnetic activity. This, in turn, affects the signature of an exoplanet in observational data. The new model must be used in order to properly interpret the data from the latest generation of space telescopes pointed at distant worlds outside our Solar System.

700 light years away from Earth in the constellation Virgo, the planet WASP-39b orbits the star WASP-39. The gas giant, which takes little more than four days to complete one orbit, is one of the best-studied exoplanets: Shortly after its commissioning in July 2022, NASA's James Webb Space Telescope turned its high-precision gaze on the distant planet. The data revealed evidence of large quantities of water vapor, of methane and even, for the first time, of carbon dioxide in the atmosphere of WASP-39b. A minor sensation! But there is still one fly in the ointment: researchers have not yet succeeded in reproducing all the crucial details of the observations in model calculations. This stands in the way of an even more precise analyses of the data. In the new study led by the MPS, the authors, including researchers from the Massachusetts Institute of Technology (USA), the Space Telescope Science Institute (USA), Keele University (United Kingdom), and the University of Heidelberg (Germany), show a way to overcome this obstacle.

"The problems arising when interpreting the data from WASP-39b are well known from many other exoplanets -- regardless whether they are observed with Kepler, TESS, James Webb, or the future PLATO spacecraft," explains MPS scientist Dr. Nadiia Kostogryz, first author of the new study. "As with other stars orbited by exoplanets, the observed light curve of WASP-39 is flatter than previous models can explain," she adds.

Researchers define a light curve as a measurement of the brightness of a star over a longer period of time. The brightness of a star fluctuates constantly, for example because its luminosity is subject to natural fluctuations. Exoplanets can also leave traces in the light curve. If an exoplanet passes in front of its star as seen by an observer, it dims the starlight. This is reflected in the light curve as a regularly recurring drop in brightness. Precise evaluations of such curves provide information about the size and orbital period of the planet. Researchers can also obtain information about the composition of the planet's atmosphere, if the light from the star is split into its different wavelengths or colours.

A close look at a star's brightness distribution

The limb of a star, the edge of the stellar disk, plays a decisive role in the interpretation of its light curve. Just as in the case of the Sun, the limb appears darker to the observer than the inner area. However, the star does not actually shine less brightly further out. "As the star is a sphere and its surface curved, we look into higher and therefore cooler layers at the limb than in the center," explains coauthor and MPS-Director Prof. Dr. Laurent Gizon. "This area therefore appears darker to us," he adds.

It is known that the limb darkening affects the exact shape of the exoplanet signal in the light curve: The dimming determines how steeply the brightness of a star falls during a planetary transit and then rises again. However, it has not been possible to reproduce observational data accurately using conventional models of the stellar atmosphere. The decrease of brightness was always less abrupt than the model calculations suggested. "It was clear that we were missing a crucial piece of the puzzle to precisely understand the exoplanets' signal," says MPS-Director Prof. Dr. Sami Solanki, coauthor of the current study.

Magnetic field is the missing piece of the puzzle

As the calculations published today show, the missing piece of the puzzle is the stellar magnetic field. Like the Sun, many stars generate a magnetic field deep in their interior through enormous flows of hot plasma. For the first time, the researchers were now able to include the magnetic field in their models of limb darkening. They could show that the strength of the magnetic field has an important effect: The limb darkening is pronounced in stars with a weak magnetic field, while it is weaker in those with a strong magnetic field.

The researchers were also able to prove that the discrepancy between observational data and model calculations disappears if the star's magnetic field is included in the computations. To this end, the team turned to selected data from NASA's Kepler Space Telescope, which captured the light of thousands and thousands of stars from 2009 to 2018. In a first step, the scientists modeled the atmosphere of typical Kepler stars in the presence of a magnetic field. In a second step, they then generated "artificial" observational data from these calculations. As a comparison with the real data showed, by including the magnetic field, the Kepler data is successfully reproduced.

The team also extended its considerations to data from the James Webb Space Telescope. The telescope is able to split the light of distant stars into its various wavelengths and thus search for the characteristic signs of certain molecules in the atmosphere of the discovered planets. As it turns out, the magnetic field of the parent star influences the stellar limb darkening differently at different wavelengths -- and should therefore be taken into account in future evaluations in order to achieve even more precise results.

From telescopes to models

"In the past decades and years, the way to move forward in exoplanet research was to improve the hardware, the space telescopes designed to search for and characterize new worlds. The James Webb Space Telescope has pushed this development to new limits," says Dr. Alexander Shapiro, coauthor of the current study and head of an ERC-funded research group at the MPS. "The next step is now to improve and refine the models to interpret this excellent data," he adds.

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Telescope detects unprecedented behavior from nearby magnetar

Researchers using Murriyang, CSIRO's Parkes radio telescope, have detected unusual radio pulses from a previously dormant star with a powerful magnetic field.

​New results published today in Nature Astronomy describe radio signals from magnetar XTE J1810-197 behaving in complex ways.

​Magnetars are a type of neutron star and the strongest magnets in the Universe.

At roughly 8,000 light years away, this magnetar is also the closest known to Earth.

​Most are known to emit polarised light, though the light this magnetar is emitting is circularly polarised, where the light appears to spiral as it moves through space.

​Dr Marcus Lower, a postdoctoral fellow at Australia's national science agency -- CSIRO, led the latest research and said the results are unexpected and totally unprecedented.

​"Unlike the radio signals we've seen from other magnetars, this one is emitting enormous amounts of rapidly changing circular polarisation. We had never seen anything like this before," Dr Lower said.

​Dr Manisha Caleb from the University of Sydney and co-author on the study said studying magnetars offers insights into the physics of intense magnetic fields and the environments these create.

​"The signals emitted from this magnetar imply that interactions at the surface of the star are more complex than previous theoretical explanations."

​Detecting radio pulses from magnetars is already extremely rare: XTE J1810-197 is one of only a handful known to produce them.

​While it's not certain why this magnetar is behaving so differently, the team has an idea.

​"Our results suggest there is a superheated plasma above the magnetar's magnetic pole, which is acting like a polarising filter," Dr Lower said.

​"How exactly the plasma is doing this is still to be determined."

​XTE J1810-197 was first observed to emit radio signals in 2003.

Then it went silent for well over a decade. The signals were again detected by the University of Manchester's 76-m Lovell telescope at the Jodrell Bank Observatory in 2018 and quickly followed up by Murriyang, which has been crucial to observing the magnetar's radio emissions ever since.

​The 64-m diameter telescope on Wiradjuri Country is equipped with a cutting edge ultra-wide bandwidth receiver.

The receiver was designed by CSIRO engineers who are world leaders in developing technologies for radio astronomy applications.

​The receiver allows for more precise measurements of celestial objects, especially magnetars, as it is highly sensitive to changes in brightness and polarisation across a broad range of radio frequencies.

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Ultrablack coating could make next-gen telescopes even better

Sometimes, seeing clearly requires complete black. For astronomy and precision optics, coating devices in black paint can cut down on stray light, enhancing images and boosting performance. For the most advanced telescopes and optical systems, every little bit matters, so their manufacturers seek out the blackest blacks to coat them.

In the Journal of Vacuum Science & Technology A, by AIP Publishing, researchers from the University of Shanghai for Science and Technology and the Chinese Academy of Sciences developed an ultrablack thin-film coating for aerospace-grade magnesium alloys.

Their coating absorbs 99.3% of light while being durable enough to survive in harsh conditions.

For telescopes operating in the vacuum of space, or optical equipment in extreme environments, existing coatings are often insufficient.

"Existing black coatings like vertically aligned carbon nanotubes or black silicon are limited by fragility," said author Yunzhen Cao.

"It is also difficult for many other coating methods to apply coatings inside a tube or on other complicated structures. This is important for their application in optical devices as they often have significant curvature or intricate shapes."

To solve these problems, the researchers turned to atomic layer deposition (ALD). With this vacuum-based manufacturing technique, the target is placed in a vacuum chamber and sequentially exposed to specific types of gas, which adhere to the object's surface in thin layers.

"One big advantage of the ALD method lies in its excellent step-coverage ability, which means we can obtain uniform film coverage on very complex surfaces, such as cylinders, pillars, and trenches," said Cao.

To make their ultrablack coating, the team used alternating layers of aluminum-doped titanium carbide (TiAlC) and silicon nitride (SiO2). The two materials work together to prevent nearly all light from reflecting off the coated surface.

"TiAlC acted as an absorbing layer, and SiO2 was employed to create an anti-reflection structure," said Cao.

"As a result, nearly all of the incident light is trapped in the multilayer film, achieving efficient light absorption."

In tests, the team found an average absorption of 99.3% across a wide range of light wavelengths, from violet light at 400 nanometers all the way to near infrared at 1,000 nanometers.

Using a special barrier layer, they even applied their coating to magnesium alloys, which are often used in aerospace applications but are easily corroded.

"What's more, the film shows superb stability in adverse environments, and is tough enough to withstand friction, heat, damp conditions, and extreme temperature changes," said Cao.

The authors hope their coating will be used to enhance space telescopes and optical hardware operating in the most extreme conditions and are working to further improve its performance.

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Researchers spying for signs of life among exoplanet atmospheres

The next generation of advanced telescopes could sharpen the hunt for potential extraterrestrial life by closely scrutinizing the atmospheres of nearby exoplanets, new research suggests.

The next generation of advanced telescopes could sharpen the hunt for potential extraterrestrial life by closely scrutinizing the atmospheres of nearby exoplanets, new research suggests.

Published recently in The Astronomical Journal, a new paper details how a team of astronomers from The Ohio State University examined upcoming telescopes' ability to detect chemical traces of oxygen, carbon dioxide, methane and water on 10 rocky exoplanets. These elements are biosignatures also found in Earth's atmosphere that can provide key scientific evidence of life.

The study found that for a pair of these nearby worlds, Proxima Centauri b and GJ 887 b, these telescopes are highly adept at detecting the presence of potential biosignatures. Of the two, findings show that only for Proxima Centauri b would the machines be able to detect carbon dioxide if it were present. Though no exoplanet has been found to precisely twin Earth's early conditions for life, this work suggests that if examined in greater detail, such unique Super Earths -- planets more massive than Earth but smaller than Neptune -- could make a suitable target for future research missions.

To further the search for habitable planets, Huihao Zhang, lead author of the study and a senior in astronomy at Ohio State, and his colleagues also sought to determine the effectiveness of specialized imaging instruments like the James Webb Space Telescope (JWST) and other Extremely Large Telescopes (ELTs) such as the European Extremely Large Telescope, the Thirty-Meter-Telescope and the Giant Magellan Telescope at directly imaging exoplanets.

"Not every planet is suitable for direct imaging, but that's why simulations give us a rough idea of what the ELTs would have delivered and the promises they're meant to hold when they are built," said Zhang.

The direct method of imaging exoplanets involves using a coronagraph or starshade to block a host star's light, allowing for scientists to capture a faint image of the new world in orbit. But because locating them in this way can be difficult and time-consuming, the researchers aimed to see how well the ELT telescopes might handle the challenge. To do this, they tested each telescope's instruments' abilities to differentiate universal background noise from the planetary noise they aimed to capture while detecting biosignatures; called the signal-to-noise ratio, the higher it is, the easier a planet's wavelength is able to be detected and analyzed.

Results showed that the direct imaging mode of one of the European ELT's instruments, called the Mid-infrared ELT Imager and Spectrograph, performed better for three planets (GJ 887 b, Proxima b and Wolf 1061 c) in discerning the presence of methane, carbon dioxide and water, while its High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph instrument could detect methane, carbon dioxide, oxygen and water, but needed a great deal more exposure time.

Additionally, since these conclusions were about instruments that will have to peer through the chemical fog of Earth's atmosphere to progress the search for cosmic life, they were compared to JWST's current outer space capabilities, said Zhang.

"It's hard to say whether space telescopes are better than ground-based telescopes, because they're different," he said. "They have different environments, different locations, and their observations have different influences."

In this case, findings revealed that while GJ 887 b is one of the most suitable targets for ELT direct imaging as its location and size result in an especially high signal-to-noise ratio, for some transiting planets, such as the TRAPPIST-1 system, JWST's techniques for studying planetary atmospheres are more suitable for detecting them than direct imaging from the ELTs on Earth.

But because the study took on a more conservative assumption with the data, Zhang said, the true effectiveness of future astronomical tools could still surprise scientists. And subtle contrasts in performance aside, these powerful technologies serve to widen our understanding of the universe and are meant to complement each other, said Ji Wang, co-author of the study and an assistant professor in astronomy at Ohio State. It's why studies like this one, that assess the limitations of those technologies, is necessary, he said.

"The importance of simulation, especially for missions that cost billions of dollars, cannot be stressed enough," said Wang. "Not only do people have to build the hardware, they also try really hard to simulate the performance and be prepared to achieve those glorious results."

In all likelihood, as the ELTs won't be completed until the tail end of the decade, researchers' next steps will settle around simulating how well future ELT instruments will take to investigating the intricacies of our own planet's rampant proofs of life.

"We want to see to what extent we can study our atmosphere to exquisite detail and how much information we can extract from it," said Wang. "Because if we cannot answer habitability questions with Earth's atmosphere, then there's no way we can start to answer these questions around other planets."

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Unexpected chemistry reveals cosmic star factories´ secrets

Two galaxies in the early universe, which contain extremely productive star factories, have been studied by a team of scientists led by Chalmers University of Technology in Sweden. Using powerful telescopes to split the galaxies' light into individual colours, the scientists were amazed to discover light from many different molecules -- more than ever before at such distances. Studies like this could revolutionise our understanding of the lives of the most active galaxies when the universe was young, the researchers believe.

When the universe was young, galaxies were very different from today's stately spirals, which are full of gently-shining suns and colourful gas clouds. New stars were being born, at rates hundreds of times faster than in today's universe. Most of this however, was hidden behind thick layers of dust, making it a challenge for scientists to discover these star factories' secrets -- until now. By studying the most distant galaxies visible with powerful telescopes, astronomers can get glimpses of how these factories managed to create so many stars.

In a new study, published in the journal Astronomy & Astrophysics, a team of scientists led by Chalmers astronomer Chentao Yang, used the telescopes of NOEMA (NOrthern Extended Millimetre Array) in France to find out more about how these early star factories managed to create so many stars. Yang and his colleagues measured light from two luminous galaxies in the early universe -- one of them classified as a quasar, and both with high rates of star formation.

"We knew these galaxies were prodigious star factories, perhaps amongst the biggest the universe has ever seen. To be able to find out how they work, we measured their light at wavelengths around one millimetre, hoping to collect new clues," says Chentao Yang.

Dramatic chemistry in the distant galaxies excites the astronomers

The measurements proved to be successful beyond the scientists' expectations. In the light they recorded from both galaxies, they identified traces of many different kinds of molecules. From deep within these galaxies, light is emitted in many different wavelengths from the clouds of gas and dust where new stars are born.

"It's an amazing explosion of colour, in shades that the human eye can't see. But by combining our observations with our knowledge of physics and chemistry, we can understand what the colours mean, and see what differences there are between different galaxies," explains Sergio Martín, astronomer at ESO and Joint ALMA Observatory, Chile, and member of the research team.

By analysing each galaxy's spectrum -- the individual colours of their light -- the scientists were able to identify 13 molecules, several of which have never been seen before in such distant galaxies. Each molecule gives different clues about the temperature, pressure, and density in the space between the stars, and about how starlight, radiation and matter interact -- providing key new information on the physical and chemical conditions in these galaxies.

"Interpreting the signals is a challenge. We are seeing part of the electromagnetic spectrum that is hard to observe in nearby galaxies. But thanks to the expansion of the universe, the light from distant galaxies like these is shifted to longer wavelengths that we can see with radio telescopes observing in the sub-millimetre," says Chentao Yang.

More like a neon-lit city than a night under the stars

The two galaxies studied by the team are so far away that their light takes almost 13 billion years to reach us.

"Looking at these galaxies is less like a night under the stars and more like seeing a city lit with neon lights," says Susanne Aalto, Chalmers astronomer and team member.

Astronomers are used to taking pictures of our galaxy's star factories, like the Orion Nebula and the Carina Nebula, she explains.

"In these two distant galaxies, we are instead seeing star factories that are bigger, brighter, full of dust, and different in many ways. The Orion and Carina nebulae are lit up thanks to ultraviolet light from hot, newborn stars. In these two distant galaxies, ultraviolet light can't get past the layers of dust. Much of the illumination is instead thanks to cosmic rays -- high energy particles that can be created by exploding stars, or close to a supermassive black hole," says Susanne Aalto.

The galaxies in the early universe can now tell their stories

While galaxies like these two are rare, the scientists have plans to study more of them, using both NOEMA and its even bigger sister telescope, ALMA (the Atacama Large Millimetre/Submillimetre Array) in Chile. Both telescopes are sensitive to light with wavelengths of around one millimetre.

"Our results show how NOEMA, with its broadband receivers and powerful correlator computer, has opened up new opportunities for studying extreme galaxies like these in the northern sky. From the southern hemisphere, ALMA's planned wideband sensitivity upgrades will offer even more exciting prospects. The most remarkable galaxies in the early universe are finally able to tell their stories through their molecules," says Pierre Cox, astronomer at CNRS and Sorbonne Université, France.

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'Jurassic worlds' might be easier to spot than modern Earth

Things may not have ended well for dinosaurs on Earth, but Cornell University astronomers say the "light fingerprint" of the conditions that enabled them to emerge here provide a crucial missing piece in our search for signs of life on planets orbiting alien stars.

Their analysis of the most recent 540 million years of Earth's evolution, known as the Phanerozoic Eon, finds that telescopes could better detect potential chemical signatures of life in the atmosphere of an Earth-like exoplanet more closely resembling the age the dinosaurs inhabited than the one we know today.

Two key biosignature pairs -- oxygen and methane, and ozone and methane -- appeared stronger in models of Earth roughly 100 million to 300 million years ago, when oxygen levels were significantly higher. The models simulated the transmission spectra, or light fingerprint, generated by an atmosphere that absorbs some colors of starlight and lets others filter through, information scientists use to determine the atmosphere's composition.

"Modern Earth's light fingerprint has been our template for identifying potentially habitable planets, but there was a time when this fingerprint was even more pronounced -- better at showing signs of life," said Lisa Kaltenegger, director of the Carl Sagan Institute (CSI) and associate professor of astronomy. "This gives us hope that it might be just a little bit easier to find signs of life -- even large, complex life -- elsewhere in the cosmos."

Kaltenegger is co-author of "Oxygen Bounty for Earth-like Exoplanets: Spectra of Earth Through the Phanerozoic," published in Monthly Notices of the Royal Astronomical Society: Letters. First author, Rebecca Payne, research associate at CSI, led the new models that details a critical epoch including the origins of land plants, animals and dinosaurs.

Using estimates from two established climate models (called GEOCARB and COPSE), the researchers simulated Earth's atmospheric composition and resulting transmission spectra over five 100-million-year increments of the Phanerozoic. Each features significant changes as a complex ocean biosphere diversified, forests proliferated and terrestrial biospheres flourished, influencing the mix of oxygen and other gasses in the atmosphere.

"It's only the most recent 12% or so of Earth's history, but it encompasses pretty much all of the time in which life was more complex than sponges," said Payne. "These light fingerprints are what you'd search for elsewhere, if you were looking for something more advanced than a single-celled organism."

While similar evolutionary processes may or may not unfold on exoplanets, Payne and Kaltenegger said their models fill in a missing puzzle piece of what a Phanerozoic would look like to a telescope, creating new templates for habitable planets with varying atmospheric oxygen levels.

Kaltenegger pioneered modeling of what Earth would look like to faraway observers based on changes over time in its geology, climate and atmosphere -- our "ground truth," she said, for identifying potential evidence of life on other worlds.

To date, about 35 rocky exoplanets have been discovered in habitable zones where liquid water could exist, Kaltenegger said. Analyzing an exoplanet's atmosphere -- if it has one -- is at the edge of technical capability for NASA's James Webb Space Telescope but is now a possibility. But, the researchers said, scientists need to know what to look for. Their models identify planets like Phanerozoic Earth as the most promising targets for finding life in the cosmos.

They also allow scientists to entertain the possibility -- purely theoretical -- that if a habitable exoplanet is discovered to have an atmosphere with 30% oxygen, life there might not be limited to microbes, but could include creatures as large and varied as the megalosauruses or microraptors that once roamed Earth.

"If they're out there," Payne said, "this sort of analysis lets us figure out where they could be living."

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Telescopes help unravel pulsar puzzle

With a remarkable observational campaign that involved 12 telescopes both on the ground and in space, including three European Southern Observatory (ESO) facilities, astronomers have uncovered the strange behaviour of a pulsar, a super-fast-spinning dead star. This mysterious object is known to switch between two brightness modes almost constantly, something that until now has been an enigma. But astronomers have now found that sudden ejections of matter from the pulsar over very short periods are responsible for the peculiar switches.

"We have witnessed extraordinary cosmic events where enormous amounts of matter, similar to cosmic cannonballs, are launched into space within a very brief time span of tens of seconds from a small, dense celestial object rotating at incredibly high speeds," says Maria Cristina Baglio, researcher at New York University Abu Dhabi, affiliated with the Italian National Institute for Astrophysics (INAF), and the lead author of the paper published today in Astronomy & Astrophysics.

A pulsar is a fast-rotating, magnetic, dead star that emits a beam of electromagnetic radiation into space. As it rotates, this beam sweeps across the cosmos -- much like a lighthouse beam scanning its surroundings -- and is detected by astronomers as it intersects the line of sight to Earth. This makes the star appear to pulse in brightness as seen from our planet.

PSR J1023+0038, or J1023 for short, is a special type of pulsar with a bizarre behaviour. Located about 4500 light-years away in the Sextans constellation, it closely orbits another star. Over the past decade, the pulsar has been actively pulling matter off this companion, which accumulates in a disc around the pulsar and slowly falls towards it.

Since this process of accumulating matter began, the sweeping beam virtually vanished and the pulsar started incessantly switching between two modes. In the 'high' mode, the pulsar gives off bright X-rays, ultraviolet and visible light, while in the 'low' mode it's dimmer at these frequencies and emits more radio waves. The pulsar can stay in each mode for several seconds or minutes, and then switch to the other mode in just a few seconds. This switching has thus far puzzled astronomers.

"Our unprecedented observing campaign to understand this pulsar's behaviour involved a dozen cutting-edge ground-based and space-borne telescopes," says Francesco Coti Zelati, a researcher at the Institute of Space Sciences, Barcelona, Spain, and co-lead author of the paper. The campaign included ESO's Very Large Telescope (VLT) and ESO's New Technology Telescope (NTT), which detected visible and near-infrared light, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner. Over two nights in June 2021, they observed the system make over 280 switches between its high and low modes.

"We have discovered that the mode switching stems from an intricate interplay between the pulsar wind, a flow of high-energy particles blowing away from the pulsar, and matter flowing towards the pulsar," says Coti Zelati, who is also affiliated with INAF.

In the low mode, matter flowing towards the pulsar is expelled in a narrow jet perpendicular to the disc. Gradually, this matter accumulates closer and closer to the pulsar and, as this happens, it is hit by the wind blowing from the pulsating star, causing the matter to heat up. The system is now in a high mode, glowing brightly in the X-ray, ultraviolet and visible light. Eventually, blobs of this hot matter are removed by the pulsar via the jet. With less hot matter in the disc, the system glows less brightly, switching back into the low mode.

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Mysterious Neptune dark spot detected from Earth for the first time

Using ESO's Very Large Telescope (VLT), astronomers have observed a large dark spot in Neptune's atmosphere, with an unexpected smaller bright spot adjacent to it. This is the first time a dark spot on the planet has ever been observed with a telescope on Earth. These occasional features in the blue background of Neptune's atmosphere are a mystery to astronomers, and the new results provide further clues as to their nature and origin.

Large spots are common features in the atmospheres of giant planets, the most famous being Jupiter's Great Red Spot. On Neptune, a dark spot was first discovered by NASA's Voyager 2 in 1989, before disappearing a few years later. "Since the first discovery of a dark spot, I've always wondered what these short-lived and elusive dark features are," says Patrick Irwin, Professor at the University of Oxford in the UK and lead investigator of the study published today in Nature Astronomy.

Irwin and his team used data from ESO's VLT to rule out the possibility that dark spots are caused by a 'clearing' in the clouds. The new observations indicate instead that dark spots are likely the result of air particles darkening in a layer below the main visible haze layer, as ices and hazes mix in Neptune's atmosphere.

Coming to this conclusion was no easy feat because dark spots are not permanent features of Neptune's atmosphere and astronomers had never before been able to study them in sufficient detail. The opportunity came after the NASA/ESA Hubble Space Telescope discovered several dark spots in Neptune's atmosphere, including one in the planet's northern hemisphere first noticed in 2018. Irwin and his team immediately got to work studying it from the ground -- with an instrument that is ideally suited to these challenging observations.

Using the VLT's Multi Unit Spectroscopic Explorer (MUSE), the researchers were able to split reflected sunlight from Neptune and its spot into its component colours, or wavelengths, and obtain a 3D spectrum. This meant they could study the spot in more detail than was possible before. "I'm absolutely thrilled to have been able to not only make the first detection of a dark spot from the ground, but also record for the very first time a reflection spectrum of such a feature," says Irwin.

Since different wavelengths probe different depths in Neptune's atmosphere, having a spectrum enabled astronomers to better determine the height at which the dark spot sits in the planet's atmosphere. The spectrum also provided information on the chemical composition of the different layers of the atmosphere, which gave the team clues as to why the spot appeared dark.

The observations also offered up a surprise result. "In the process we discovered a rare deep bright cloud type that had never been identified before, even from space," says study co-author Michael Wong, a researcher at the University of California, Berkeley, USA. This rare cloud type appeared as a bright spot right beside the larger main dark spot, the VLT data showing that the new 'deep bright cloud' was at the same level in the atmosphere as the main dark spot. This means it is a completely new type of feature compared to the small 'companion' clouds of high-altitude methane ice that have been previously observed.

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Astronomers discover last three planets Kepler telescope observed before going dark

More than 5,000 planets are confirmed to exist beyond our solar system. Over half were discovered by NASA's Kepler Space Telescope, a resilient observatory that far outlasted its original planned mission. Over nine and a half years, the spacecraft trailed the Earth, scanning the skies for periodic dips in starlight that could signal the presence of a planet crossing in front of its star.

In its last days, the telescope kept recording the brightness of stars as it was running out of fuel. On Oct. 30, 2018, its fuel tanks depleted, the spacecraft was officially retired.

Now, astronomers at MIT and the University of Wisconsin at Madison, with the help of citizen scientists, have discovered what may be the last planets that Kepler gazed upon before going dark.

The team combed through the telescope's last week of high-quality data and spotted three stars, in the same part of the sky, that appeared to dim briefly. The scientists determined that two of the stars each host a planet, while the third hosts a planet "candidate" that has yet to be verified.

The two validated planets are K2-416 b, a planet that is about 2.6 times the size of the Earth and that orbits its star about every 13 days, and K2-417 b, a slightly larger planet that is just over three times Earth's size and that circles its star every 6.5 days. For their size and proximity to their stars, both planets are considered "hot mini-Neptunes ." They are located about 400 light years from Earth.

The planet candidate is EPIC 246251988 b -- the largest of the three worlds at almost four times the size of the Earth. This Neptune-sized candidate orbits its star in around 10 days, and is slightly farther away, 1,200 light years from Earth.

"We have found what are probably the last planets ever discovered by Kepler, in data taken while the spacecraft was literally running on fumes," says Andrew Vanderburg, assistant professor of physics in MIT's Kavli Institute for Astrophysics and Space Research. "The planets themselves are not particularly unusual, but their atypical discovery and historical importance makes them interesting."

The team has published their discovery today in the journal Monthly Notices of the Royal Astronomical Society. Vanderburg's co-authors are lead author Elyse Incha, at the University of Wisconsin at Madison, and amateur astronomers Tom Jacobs and Daryll LaCourse, along with scientists at NASA, the Center for Astrophysics of Harvard and the Smithsonian, and the University of North Carolina at Chapel Hill.

Data squeeze

In 2009, NASA launched the Kepler telescope into space, where it followed the Earth's orbit and continuously monitored millions of stars in a patch of the northern sky. Over four years, the telescope recorded the brightness of over 150,000 stars, which astronomers used to discover thousands of possible planets beyond our solar system.

Kepler kept observing beyond its original three-and-a-half-year mission, until May 2013, when the second of four reaction wheels failed. The wheels served as the spacecraft's gyroscopes, helping to keep the telescope pointed at a particular point in the sky. Kepler's observations were put on pause while scientists searched for a fix.

One year later, Kepler restarted as "K2," a reworked mission that used the sun's wind to balance the unsteady spacecraftin a way that kept the telescope relatively stable for a few months at a time -- a period called a campaign. K2 went on for another four years, observing over half a million more stars before the spacecraft finally ran out of fuel during its 19th campaign. The data from this last campaign comprised only a week of high-quality observations and another 10 days of noisier measurements as the spacecraft rapidly lost fuel.

"We were curious to see whether we could get anything useful out of this short dataset," Vanderburg says. "We tried to see what last information we could squeeze out of it."

By eye

Vanderburg and Incha presented the challenge to the Visual Survey Group, a team of amateur and professional astronomers who hunt for exoplanets in satellite data. They search by eye through thousands of recorded light curves of each star, looking for characteristic dips in brightness that signal a "transit," or the possible crossing of a planet in front of its star.

The citizen scientists are especially suited to combing through short datasets such as K2's very last campaign.

"They can distinguish transits from other wacky things like a glitch in the instrument," Vanderburg says. "That's helpful especially when your data quality begins to suffer, like it did in K2's last bit of data."

The astronomers spent a few days efficiently looking through the light curves that Kepler recorded from about 33,000 stars. The team worked with only a week's worth of high-quality data from the telescope before it began to lose fuel and focus. Even in this short window of data, the team was able to spot a single transit in three different stars.

Incha and Vanderburg then looked at the telescope's very last, lower-quality observations, taken in its last 11 days of operation, to see if they could spot any additional transits in the same three stars -- evidence that a planet was periodically circling its star.

During this 11-day period, as the spacecraft was losing fuel, its thrusters fired more erratically, causing the telescope's view to drift. In their analysis, the team focused on the region of each star's light curves between thruster activity, to see if they could spot any additional transits in these less data-noisy moments.

This search revealed a second transit for K2-416 b and K2-417 b, validating that they each host a planet. The team also detected a similar dip in brightness for K2-417 b in data taken of the same star by NASA's Transiting Exoplanet Survey Satellite (TESS), a mission that is led and operated by MIT. Data from TESS helped to confirm the planet candidate around this star.

"Those two are pretty much, without a doubt, planets," Incha says. "We also followed up with ground-based observations to rule out all kinds of false positive scenarios for them, including background star interference, and close-in stellar binaries."

"These are the last chronologically observed planets by Kepler, but every bit of the telescope's data is incredibly useful," Incha says. "We want to make sure none of that data goes to waste, because there are still a lot of discoveries to be made."

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Making better measurements of the composition of galaxies

A study using data from telescopes on Earth and in the sky resolves a problem plaguing astronomers working in the infrared and could help make better observations of the composition of the universe with the James Webb Space Telescope and other instruments. The work is published April 20 in Nature Astronomy.

"We're trying to measure the composition of gases inside galaxies," said Yuguang Chen, a postdoctoral researcher working with Professor Tucker Jones in the Department of Physics and Astronomy at the University of California, Davis.

Most elements other than hydrogen, helium and lithium are produced inside stars, so the composition and distribution of heavier elements -- especially the ratio of oxygen to hydrogen -- can help astronomers understand how many and what kinds of stars are being formed in a distant object.

Astronomers use two methods to measure oxygen in a galaxy, but unfortunately, they give different results. One common method, collisionally excited lines, gives a strong signal, but the results are thought to be sensitive to temperature changes, Chen said. A second method uses a different set of lines, called recombination lines, which are fainter but not thought to be affected by temperature.

The recombination line method consistently produces measurements about double those from collisionally excited lines. Scientists attribute the discrepancy to temperature fluctuations in gas clouds, but this has not been directly proven, Chen said.

Chen, Jones and colleagues used optical and infrared astronomy to measure oxygen abundance in dwarf galaxy Markarian 71, about 11 million light years from Earth. They used archived data from the recently retired SOFIA flying telescope and the retired Herschel Space Observatory, as well as making observations with telescopes at the W.M. Keck Observatory in Mauna Kea, Hawaii.

SOFIA (Stratospheric Observatory For Infrared Astronomy) was a telescope mounted in a Boeing 747 aircraft. By flying at 38,000 to 45,000 feet, the aircraft could get above 99% of the water vapor in Earth's atmosphere, which effectively blocks infrared light from deep space from reaching ground level. A joint project of NASA and the German space agency, SOFIA made its last operational flight in September 2022 and is now headed for a museum display in Tucson.

The Herschel Space Observatory, named after astronomers William and Caroline Herschel, was an infrared space telescope operated by the European Space Agency. It was active from 2009 to 2013.

A surprising result

With data from these instruments, Chen and Jones examined oxygen abundance in Markarian 71 while correcting for temperature fluctuations. They found that the result from collisionally excited infrared lines was still 50% less than that from the recombination line method, even after eliminating the effect of temperature.

"This result is very surprising to us," Chen said. There is no consensus on an explanation for the discrepancy, he said. The team plans to look at additional objects to figure out what properties of galaxies correlate with this variation, Chen said.

One of the goals of the James Webb Space Telescope, launched in 2022, is to make infrared observations of the composition of distant galaxies in the first billion years of the universe. The new results provide a framework for making these measurements with the JWST and the Atacama Large Millimeter Array in Chile.

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Could this copycat black hole be a new type of star?

It looks like a black hole and bends light like a black hole, but it could actually be a new type of star.

Though the mysterious object is a hypothetical mathematical construction, new simulations by Johns Hopkins researchers suggest there could be other celestial bodies in space hiding from even the best telescopes on Earth. The findings are set to publish in Physical Review D.

"We were very surprised," said Pierre Heidmann, a Johns Hopkins University physicist who led the study. "The object looks identical to a black hole, but there's light coming out from its dark spot."

The detection of gravitational waves in 2015 rocked the world of astrophysics because it confirmed the existence of black holes. Inspired by those findings, the Johns Hopkins team set out to explore the possibility of other objects that could produce similar gravitational effects but that could be passing as black holes when observed with ultraprecise sensors on Earth, said co-author and Johns Hopkins physicist Ibrahima Bah.

"How would you tell when you don't have a black hole? We don't have a good way to test that," Bah said. "Studying hypothetical objects like topological solitons will help us figure that out as well."

The new simulations realistically depict an object the Johns Hopkins team calls a topological soliton. The simulations show an object looking like a blurry photo of a black hole from afar but like something else entirely up close.

The object is hypothetical at this stage. But the fact that the team could construct it using mathematical equations and show what it looks like with simulations suggests there could be other types of celestial bodies in space hiding from even the best telescopes on Earth.

The findings show how the topological soliton distorts space exactly as a black hole does -- but behaves unlike a black hole as it scrambles and releases weak light rays that would not escape the strong gravitational force of a true hole.

"Light is strongly bent, but instead of being absorbed like it would in a black hole, it scatters in funky motions until at one point it comes back to you in a chaotic manner," Heidmann said. "You don't see a dark spot. You see a lot of blur, which means light is orbiting like crazy around this weird object."

A black hole's gravitational field is so intense that light can orbit around it at a certain distance from its center, in the same way that Earth orbits the sun. This distance determines the edge of the hole's "shadow," so that any incoming light will fatally hit the region that scientists call the "event horizon." There, nothing can escape -- not even light.

The Hopkins team simulated several scenarios using pictures of outer space as if they had been captured with a camera, placing a black hole and the topological soliton in front of the lens. The results produced distorted pictures because of the gravitational effects of the massive bodies.

"These are the first simulations of astrophysically relevant string theory objects, since we can actually characterize the differences between a topological soliton and a black hole as if an observer was seeing them in the sky," Heidmann said.

Motivated by various results from string theory, Bah and Heidmann discovered ways to construct topological solitons using Einstein's theory of general relativity in 2021. While the solitons are not predictions of new objects, they serve as the best models of what new quantum gravity objects could look like compared to black holes.

Scientists have previously created models of boson stars, gravastars, and other hypothetical objects that could exert similar gravitational effects with exotic forms of matter. But the new research accounts for pillar theories of the inner workings of the universe that other models don't. It uses string theory that reconciles quantum mechanics and Einstein's theory of gravity, the researchers said.

"It's the start of a wonderful research program," Bah said. "We hope in the future to be able to genuinely propose new types of ultracompact stars consisting of new kinds of matter from quantum gravity."

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Researchers devise new membrane mirrors for large space-based telescopes

Researchers have developed a new way to produce and shape large, high-quality mirrors that are much thinner than the primary mirrors previously used for telescopes deployed in space. The resulting mirrors are flexible enough to be rolled up and stored compactly inside a launch vehicle.

"Launching and deploying space telescopes is a complicated and costly procedure," said Sebastian Rabien from Max Planck Institute for Extraterrestrial Physics in Germany. "This new approach -- which is very different from typical mirror production and polishing procedures -- could help solve weight and packaging issues for telescope mirrors, enabling much larger, and thus more sensitive, telescopes to be placed in orbit."

In the Optica Publishing Group journal Applied Optics, Rabien reports successful fabrication of parabolic membrane mirror prototypes up to 30 cm in diameter. These mirrors, which could be scaled up to the sizes needed in space telescopes, were created by using chemical vapor deposition to grow membrane mirrors on a rotating liquid inside a vacuum chamber. He also developed a method that uses heat to adaptively correct imperfections that might occur after the mirror is unfolded.

"Although this work only demonstrated the feasibility of the methods, it lays the groundwork for larger packable mirror systems that are less expensive," said Rabien. "It could make lightweight mirrors that are 15 or 20 meters in diameter a reality, enabling space-based telescopes that are orders of magnitude more sensitive than ones currently deployed or being planned."

Applying an old process in a new way

The new method was developed during the COVID-19 pandemic, which Rabien says gave him some extra time to think and try out new concepts. "In a long series of tests, we researched many liquids to find out their usability for the process, investigated how the polymer growth can be carried out homogeneously, and worked to optimize the process," he said.

For chemical vapor deposition, a precursor material is evaporated and thermally split into monomeric molecules. Those molecules deposit on the surfaces in a vacuum chamber and then combine to form a polymer. This process is commonly used to apply coatings such as the ones that make electronics water-resistant, but this is the first time it has been used to create parabolic membrane mirrors with the optical qualities necessary for use in telescopes.

To create the precise shape necessary for a telescope mirror, the researchers added a rotating container filled with a small amount of liquid to the inside of the vacuum chamber. The liquid forms a perfect parabolic shape onto which the polymer can grow, forming the mirror base. When the polymer is thick enough, a reflective metal layer is applied to the top via evaporation and the liquid is washed away.

"It has long been known that rotating liquids that are aligned with the local gravitational axis will naturally form a paraboloid surface shape," said Rabien. "Utilizing this basic physics phenomenon, we deposited a polymer onto this perfect optical surface, which formed a parabolic thin membrane that can be used as the primary mirror of a telescope once coated with a reflecting surface such as aluminum."

Although other groups have created thin membranes for similar purposes, these mirrors are typically shaped using a high-quality optical mold. Using a liquid to form the shape is much more affordable and can be more easily scaled up to large sizes.

Reshaping a folded mirror

The thin and lightweight mirror created using this technique can easily be folded or rolled up during the trip to space. However, it would be nearly impossible to get it back to the perfect parabolic shape after unpacking. To reshape the membrane mirror, the researchers developed a thermal method that uses a localized temperature change created with light to enable adaptive shape control that can bring the thin membrane into the desired optical shape.

The researchers tested their approach by creating 30-cm diameter membrane mirrors in a vacuum deposition chamber. After much trial and error, they were able to produce high quality mirrors with a surface shape suitable for telescopes. They also showed that their thermal radiative adaptive shaping method worked well, as demonstrated with an array of radiators and illumination from a digital light projector.

The new membrane-based mirrors could also be used in adaptive optics systems. Adaptive optics can improve the performance of optical systems by using a deformable mirror to compensate for distortion in incoming light. Because the surface of the new membrane mirrors is deformable, these mirrors could be shaped with electrostatic actuators to create deformable mirrors that are less expensive to make than those created with conventional methods.

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AI algorithm unblurs the cosmos

The cosmos would look a lot better if Earth's atmosphere wasn't photo bombing it all the time.

Even images obtained by the world's best ground-based telescopes are blurry due to the atmosphere's shifting pockets of air. While seemingly harmless, this blur obscures the shapes of objects in astronomical images, sometimes leading to error-filled physical measurements that are essential for understanding the nature of our universe.

Now researchers at Northwestern University and Tsinghua University in Beijing have unveiled a new strategy to fix this issue. The team adapted a well-known computer-vision algorithm used for sharpening photos and, for the first time, applied it to astronomical images from ground-based telescopes. The researchers also trained the artificial intelligence (AI) algorithm on data simulated to match the Vera C. Rubin Observatory's imaging parameters, so, when the observatory opens next year, the tool will be instantly compatible.

While astrophysicists already use technologies to remove blur, the adapted AI-driven algorithm works faster and produces more realistic images than current technologies. The resulting images are blur-free and truer to life. They also are beautiful -- although that's not the technology's purpose.

"Photography's goal is often to get a pretty, nice-looking image," said Northwestern's Emma Alexander, the study's senior author. "But astronomical images are used for science. By cleaning up images in the right way, we can get more accurate data. The algorithm removes the atmosphere computationally, enabling physicists to obtain better scientific measurements. At the end of the day, the images do look better as well."

The research will be published March 30 in the Monthly Notices of the Royal Astronomical Society.

Alexander is an assistant professor of computer science at Northwestern's McCormick School of Engineering, where she runs the Bio Inspired Vision Lab. She co-led the new study with Tianao Li, an undergraduate in electrical engineering at Tsinghua University and a research intern in Alexander's lab.

When light emanates from distant stars, planets and galaxies, it travels through Earth's atmosphere before it hits our eyes. Not only does our atmosphere block out certain wavelengths of light, it also distorts the light that reaches Earth. Even clear night skies still contain moving air that affects light passing through it. That's why stars twinkle and why the best ground-based telescopes are located at high altitudes where the atmosphere is thinnest.

"It's a bit like looking up from the bottom of a swimming pool," Alexander said. "The water pushes light around and distorts it. The atmosphere is, of course, much less dense, but it's a similar concept."

The blur becomes an issue when astrophysicists analyze images to extract cosmological data. By studying the apparent shapes of galaxies, scientists can detect the gravitational effects of large-scale cosmological structures, which bend light on its way to our planet. This can cause an elliptical galaxy to appear rounder or more stretched than it really is. But atmospheric blur smears the image in a way that warps the galaxy shape. Removing the blur enables scientists to collect accurate shape data.

"Slight differences in shape can tell us about gravity in the universe," Alexander said. "These differences are already difficult to detect. If you look at an image from a ground-based telescope, a shape might be warped. It's hard to know if that's because of a gravitational effect or the atmosphere."

To tackle this challenge, Alexander and Li combined an optimization algorithm with a deep-learning network trained on astronomical images. Among the training images, the team included simulated data that matches the Rubin Observatory's expected imaging parameters. The resulting tool produced images with 38.6% less error compared to classic methods for removing blur and 7.4% less error compared to modern methods.

When the Rubin Observatory officially opens next year, its telescopes will begin a decade-long deep survey across an enormous portion of the night sky. Because the researchers trained the new tool on data specifically designed to simulate Rubin's upcoming images, it will be able to help analyze the survey's highly anticipated data.

For astronomers interested in using the tool, the open-source, user-friendly code and accompanying tutorials are available online.

"Now we pass off this tool, putting it into the hands of astronomy experts," Alexander said. "We think this could be a valuable resource for sky surveys to obtain the most realistic data possible."

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Extensive catalog of exploding stars

Celestial phenomena that change with time such as exploding stars, mysterious objects that suddenly brighten and variable stars are a new frontier in astronomical research, with telescopes that can rapidly survey the sky revealing thousands of these objects.

The largest data release of relatively nearby supernovae (colossal explosions of stars), containing three years of data from the University of Hawaiʻi Institute for Astronomy's (IfA) Pan-STARRS telescope atop Haleakalā on Maui, is publicly available via the Young Supernova Experiment (YSE). The project, which began in 2019, surveyed more than 1,500 square degrees of sky every three days, and discovered thousands of new cosmic explosions and other astrophysical transients, dozens of them just days or hours after exploding.

The newly-released data contains information on nearly 2,000 supernovae and other luminous variable objects with observations in multiple colors. It is also the first to extensively use the multi-color imaging to classify the supernovae and estimate their distances.

Astrophysicists use large imaging surveys -- systematic studies of large areas of the sky over time -- and different parts of the electromagnetic spectrum for many scientific goals. Some are used to study distant galaxies and how they evolve over cosmic time, or look at specific regions of the sky that are especially important, such as the Andromeda Galaxy.

"Pan-STARRS produces a steady stream of transient discoveries, observing large areas of the sky every clear night with two telescopes," said Mark Huber, a senior researcher at IfA. "With over a decade of observations, Pan-STARRS operates one of the best calibrated systems in astronomy, with a detailed reference image of the static sky visible from Haleakalā. This enables rapid discovery and follow-up of supernovae and other transient events, well suited for programs like YSE to build up the sample required for analysis and this significant data release."

YSE is designed to find energetic astrophysical "transient" sources such as supernovae, tidal disruption events and kilonovae (extremely energetic explosions). These transients evolve quickly, rising to their maximum brightness and then fading away after a few days or months.

Multi-institution collaboration

The images from Pan-STARRS are transferred to UH's Information Technology Center for initial processing and scientific calibration by the Pan-STARRS Image Processing Pipeline. Higher-level processing, detailed analysis and storage was then performed using computing systems at the National Center for Supercomputing Applications' (NCSA) Center for Astrophysical Surveys (CAPS), the University of California, Santa Cruz (UCSC), and the Dark Cosmology Centre (DARK) at the Niels Bohr Institute at the University of Copenhagen.

The survey and the tools used to analyze the data are critical precursors to the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time, a new 8.4-meter telescope being built in Chile. Rubin Observatory will survey the entire sky every three nights, discovering so many variable and exploding objects that it will be impossible to obtain detailed follow-up observations. The ability to classify these objects from the survey data alone will be vital to choosing the most interesting ones for astronomers to target with other telescopes.

Gautham Narayan, deputy director of CAPS, is leading the cosmological analysis for the data sample and former CAPS graduate fellow Patrick Aleo is lead author of the paper, "The Young Supernova Experiment Data Release 1 (YSE DR1): Light Curves and Photometric Classification of 1975 Supernovae."

"Much of the time-domain universe is uncharted. We still do not know the progenitor systems of many of the most common classes of transients, such as type Ia supernovae, while still using these sources to try and understand the expansion history of our universe," Narayan said. "We've also seen one electromagnetic counterpart to a binary neutron star merger. There are many kinds of transients that are theoretically predicted, but have never been seen at all."

Ken Chambers, Pan-STARRS director, added that "this collaboration with the Young Supernova Experiment makes exceptional use of Pan-STARRS' ability to routinely survey the sky for transient phenomena and moving objects. We have provided an unprecedented sample of young supernovae discovered before their peak luminosity that will be an important resource for supernova researchers and cosmologists for many years. Looking ahead, Pan-STARRS will remain a crucial resource in the Northern Hemisphere to complement the Rubin Observatory in the Southern Hemisphere."

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Flat, pancake-sized metalens images lunar surface in an engineering first

Astronomers and amateurs alike know the bigger the telescope, the more powerful the imaging capability. To keep the power but streamline one of the bulkier components, a Penn State-led research team created the first ultrathin, compact metalens telescope capable of imaging far-away objects, including the moon.

Metalenses comprise tiny, antenna-like surface patterns that can focus light to magnify distant objects in the same way as traditional curved glass lenses, but they have the advantage of being flat. Though small, millimeters-wide metalenses have been developed in the past, the researchers scaled the size of the lens to eight centimeters in diameter, or about four inches wide, making it possible to use in large optical systems, such as telescopes. They published their approach in Nano Letters.

"Traditional camera or telescope lenses have a curved surface of varying thickness, where you have a bump in the middle and thinner edges, which causes the lens to be bulky and heavy," said corresponding author Xingjie Ni, associate professor of electrical engineering and computer science at Penn State. "Metalenses use nano-structures on the lens instead of curvature to contour light, which allows them to lay flat."

That is one of the reasons, Ni said, modern cellphone camera lenses protrude from the body of the phone: the thickness of the lenses take up space, though they appear flat since they are hidden behind a glass window.

Metalenses are typically made using electron beam lithography, which involves scanning a focused beam of electrons onto a piece of glass, or other transparent substrate, to create antenna-like patterns point by point. However, the scanning process of the electron beam limits the size of the lens that can be created, as scanning each point is time-consuming and has low throughput.

To create a bigger lens, the researchers adapted a fabrication method known as deep ultraviolet (DUV) photolithography, which is commonly used to produce computer chips.

"DUV photolithography is a high-throughput and high-yield process that can produce many computer chips within seconds," Ni said. "We found this to be a good fabrication method for metalenses because it allows for much larger pattern sizes while still maintaining small details, which allows the lens to work effectively."

The researchers modified the method with their own novel procedure, called rotating wafer and stitching. Researchers divided the wafer, on which the metalens was fabricated, into four quadrants, which were further divided into 22 by 22 millimeter regions -- smaller than a standard postage stamp. Using a DUV lithography machine at Cornell University, they projected a pattern onto one quadrant through projection lenses, which they then rotated by 90 degrees and projected again. They repeated the rotation until all four quadrants were patterned.

"The process is cost-effective because the masks containing the pattern data for each quadrant can be reused due to the rotation symmetry of the metalens," Ni said. "This reduces the manufacturing and environmental costs of the method."

As the size of the metalens increased, the digital files required to process the patterns became significantly larger, which would take a long time for the DUV lithography machine to process. To overcome this issue, the researchers compressed the files using data approximations and by referencing non-unique data.

"We utilized every possible method to reduce the file size," Ni said. "We identified identical data points and referenced existing ones, gradually reducing the data until we had a usable file to send to the machine for creating the metalens."

Using the new fabrication method, the researchers developed a single-lens telescope and captured clear images of the lunar surface -- achieving greater resolution of objects and much farther imaging distance than previous metalenses. Before the technology can be applied to modern cameras, however, researchers must address the issue of chromatic aberration, which causes image distortion and blurriness when different colors of light, which bend in different directions, enter a lens.

"We are exploring smaller and more sophisticated designs in the visible range, and will compensate for various optical aberrations, including chromatic aberration," Ni said.

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Astronomers uncover a one-in-ten-billion binary star system: Kilonova progenitor system

Astronomers using the SMARTS 1.5-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF's NOIRLab, have uncovered the first example of a phenomenally rare type of binary star system, one that has all the right conditions to eventually trigger a kilonova -- the ultra-powerful, gold-producing explosion created by colliding neutron stars. Such an arrangement is so vanishingly rare that only about 10 such systems are thought to exist in the entire Milky Way Galaxy. The findings are published today in the journal Nature.

This unusual system, known as CPD-29 2176, is located about 11,400 light-years from Earth. It was first identified by NASA's Neil Gehrels Swift Observatory. Later observations with the SMARTS 1.5-meter Telescope allowed astronomers to deduce the orbital characteristics and types of stars that make up this system -- a neutron star created by an ultra-stripped supernova and a closely orbiting massive star that is in the process of becoming an ultra-stripped supernova itself.

An ultra-stripped supernova is the end-of-life explosion of a massive star that has had much of its outer atmosphere stripped away by a companion star. This class of supernova lacks the explosive force of a traditional supernova, which would otherwise "kick" a nearby companion star out of the system.

"The current neutron star would have to form without ejecting its companion from the system. An ultra-stripped supernova is the best explanation for why these companion stars are in such a tight orbit," said Noel D. Richardson at Embry-Riddle Aeronautical University and lead author of the paper. "To one day create a kilonova, the other star would also need to explode as an ultra-stripped supernova so the two neutron stars could eventually collide and merge."

As well as representing the discovery of an incredibly rare cosmic oddity, finding and studying kilonova progenitor systems such as this can help astronomers unravel the mystery of how kilonovae form, shedding light on the origin of the heaviest elements in the Universe.

"For quite some time, astronomers speculated about the exact conditions that could eventually lead to a kilonova," said NOIRLab astronomer and co-author André-Nicolas Chené. "These new results demonstrate that, in at least some cases, two sibling neutron stars can merge when one of them was created without a classical supernova explosion."

Producing such an unusual system, however, is a long and unlikely process. "We know that the Milky Way contains at least 100 billion stars and likely hundreds of billions more. This remarkable binary system is essentially a one-in-ten-billion system," said Chené. "Prior to our study, the estimate was that only one or two such systems should exist in a spiral galaxy like the Milky Way."

Though this system has all the right stuff to eventually form a kilonova, it will be up to future astronomers to study that event. It will take at least one million years for the massive star to end its life as a titanic supernova explosion and leave behind a second neutron star. This new stellar remnant and the pre-existing neutron star will then need to gradually draw together in a cosmic ballet, slowly losing their orbital energy as gravitational radiation.

When they eventually merge, the resulting kilonova explosion will produce much more powerful gravitational waves and leave behind in its wake a large amount of heavy elements, including silver and gold.

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Were galaxies much different in the early universe?

An array of 350 radio telescopes in the Karoo desert of South Africa is getting closer to detecting "cosmic dawn" -- the era after the Big Bang when stars first ignited and galaxies began to bloom.

In a paper accepted for publication in The Astrophysical Journal, the Hydrogen Epoch of Reionization Array (HERA) team reports that it has doubled the sensitivity of the array, which was already the most sensitive radio telescope in the world dedicated to exploring this unique period in the history of the universe.

While they have yet to actually detect radio emissions from the end of the cosmic dark ages, their results do provide clues to the composition of stars and galaxies in the early universe. In particular, their data suggest that early galaxies contained very few elements besides hydrogen and helium, unlike our galaxies today.

When the radio dishes are fully online and calibrated, ideally this fall, the team hopes to construct a 3D map of the bubbles of ionized and neutral hydrogen as they evolved from about 200 million years ago to around 1 billion years after the Big Bang. The map could tell us how early stars and galaxies differed from those we see around us today, and how the universe as a whole looked in its adolescence.

"This is moving toward a potentially revolutionary technique in cosmology. Once you can get down to the sensitivity you need, there's so much information in the data," said Joshua Dillon, a research scientist in the University of California, Berkeley's Department of Astronomy and lead author of the paper. "A 3D map of most of the luminous matter in the universe is the goal for the next 50 years or more."

Other telescopes also are peering into the early universe. The new James Webb Space Telescope (JWST) has now imaged a galaxy that existed about 325 million years after the birth of the universe in the Big Bang. But the JWST can see only the brightest of the galaxies that formed during the Epoch of Reionization, not the smaller but far more numerous dwarf galaxies whose stars heated the intergalactic medium and ionized most of the hydrogen gas.

HERA seeks to detect radiation from the neutral hydrogen that filled the space between those early stars and galaxies and, in particular, determine when that hydrogen stopped emitting or absorbing radio waves because it became ionized.

The fact that the HERA team has not yet detected these bubbles of ionized hydrogen within the cold hydrogen of the cosmic dark age rules out some theories of how stars evolved in the early universe.

Specifically, the data show that the earliest stars, which may have formed around 200 million years after the Big Bang, contained few other elements than hydrogen and helium. This is different from the composition of today's stars, which have a variety of so-called metals, the astronomical term for elements, ranging from lithium to uranium, that are heavier than helium. The finding is consistent with the current model for how stars and stellar explosions produced most of the other elements.

"Early galaxies have to have been significantly different than the galaxies that we observe today in order for us not to have seen a signal," said Aaron Parsons, principal investigator for HERA and a UC Berkeley associate professor of astronomy. "In particular, their X-ray characteristics have to have changed. Otherwise, we would have detected the signal we're looking for."

The atomic composition of stars in the early universe determined how long it took to heat the intergalactic medium once stars began to form. Key to this is the high-energy radiation, primarily X-rays, produced by binary stars where one of them has collapsed to a black hole or neutron star and is gradually eating its companion. With few heavy elements, a lot of the companion's mass is blown away instead of falling onto the black hole, meaning fewer X-rays and less heating of the surrounding region.

The new data fit the most popular theories of how stars and galaxies first formed after the Big Bang, but not others. Preliminary results from the first analysis of HERA data, reported a year ago, hinted that those alternatives -- specifically, cold reionization -- were unlikely.

"Our results require that even before reionization and by as late as 450 million years after the Big Bang, the gas between galaxies must have been heated by X-rays. These likely came from binary systems where one star is losing mass to a companion black hole," Dillon said. "Our results show that if that's the case, those stars must have been very low 'metallicity,' that is, very few elements other than hydrogen and helium in comparison to our sun, which makes sense because we're talking about a period in time in the universe before most of the other elements were formed."

The Epoch of Reionization

The origin of the universe in the Big Bang 13.8 billion years ago produced a hot cauldron of energy and elementary particles that cooled for hundreds of thousands of years before protons and electrons combined to form atoms -- primarily hydrogen and helium. Looking at the sky with sensitive telescopes, astronomers have mapped in detail the faint variations in temperature from this moment -- what's known as the cosmic microwave background -- a mere 380,000 years after the Big Bang.

Aside from this relict heat radiation, however, the early universe was dark. As the universe expanded, the clumpiness of matter seeded galaxies and stars, which in turn produced radiation -- ultraviolet and X-rays -- that heated the gas between stars. At some point, hydrogen began to ionize -- it lost its electron -- and formed bubbles within the neutral hydrogen, marking the beginning of the Epoch of Reionization.

To map these bubbles, HERA and several other experiments are focused on a wavelength of light that neutral hydrogen absorbs and emits, but ionized hydrogen does not. Called the 21-centimeter line (a frequency of 1,420 megahertz), it is produced by the hyperfine transition, during which the spins of the electron and proton flip from parallel to antiparallel. Ionized hydrogen, which has lost its only electron, doesn't absorb or emit this radio frequency.

Since the Epoch of Reionization, the 21 centimeter line has been red-shifted by the expansion of the universe to a wavelength 10 times as long -- about 2 meters, or 6 feet. HERA's rather simple antennas, a construct of chicken wire, PVC pipe and telephone poles, are 14 meters across in order to collect and focus this radiation onto detectors.

"At two meters wavelength, a chicken wire mesh is a mirror," Dillon said. "And all the sophisticated stuff, so to speak, is in the supercomputer backend and all of the data analysis that comes after that."

The new analysis is based on 94 nights of observing in 2017 and 2018 with about 40 antennas -- phase 1 of the array. Last year's preliminary analysis was based on 18 nights of phase 1 observations.

The new paper's main result is that the HERA team has improved the sensitivity of the array by a factor of 2.1 for light emitted about 650 million years after the Big Bang (a redshift, or an increase in wavelength, of 7.9), and 2.6 for radiation emitted about 450 million years after the Big Bang (a redshift of 10.4).

The HERA team continues to improve the telescope's calibration and data analysis in hopes of seeing those bubbles in the early universe, which are about 1 millionth the intensity of the radio noise in the neighborhood of Earth. Filtering out the local radio noise to see the radiation from the early universe has not been easy.

"If it's Swiss cheese, the galaxies make the holes, and we're looking for the cheese," so far, unsuccessfully, said David Deboer, a research astronomer in UC Berkeley's Radio Astronomy Laboratory.

Extending that analogy, however, Dillon noted, "What we've done is we've said the cheese must be warmer than if nothing had happened. If the cheese were really cold, it turns out it would be easier to observe that patchiness than if the cheese were warm."

That mostly rules out cold reionization theory, which posited a colder starting point. The HERA researchers suspect, instead, that the X-rays from X-ray binary stars heated up the intergalactic medium first.

"The X-rays will effectively heat up the whole block of cheese before the holes will form," Dillon said. "And those holes are the ionized bits."

"HERA is continuing to improve and set better and better limits," Parsons said. "The fact that we're able to keep pushing through, and we have new techniques that are continuing to bear fruit for our telescope, is great."

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NASA's Webb draws back curtain on universe's early galaxies

A few days after officially starting science operations, NASA's James Webb Space Telescope propelled astronomers into a realm of early galaxies, previously hidden beyond the grasp of all other telescopes until now.

"Everything we see is new. Webb is showing us that there's a very rich universe beyond what we imagined," said Tommaso Treu of the University of California at Los Angeles, principal investigator on one of the Webb programs. "Once again the universe has surprised us. These early galaxies are very unusual in many ways."

Two research papers, led by Marco Castellano of the National Institute for Astrophysics in Rome, Italy, and Rohan Naidu of the Harvard-Smithsonian Center for Astrophysics and the Massachusetts Institute of Technology in Cambridge, Massachusetts, have been published in the Astrophysical Journal Letters.

These initial findings are from a broader Webb research initiative involving two Early Release Science (ERS) programs: the Grism Lens-Amplified Survey from Space (GLASS), and the Cosmic Evolution Early Release Science Survey (CEERS).

With just four days of analysis, researchers found two exceptionally bright galaxies in the GLASS-JWST images. These galaxies existed approximately 450 and 350 million years after the big bang (with a redshift of approximately 10.5 and 12.5, respectively), though future spectroscopic measurements with Webb will help confirm.

"With Webb, we were amazed to find the most distant starlight that anyone had ever seen, just days after Webb released its first data," said Naidu of the more distant GLASS galaxy, referred to as GLASS-z12, which is believed to date back to 350 million years after big bang. The previous record holder is galaxy GN-z11, which existed 400 million years after the big bang (redshift 11.1), and was identified in 2016 by Hubble and Keck Observatory in deep-sky programs.

"Based on all the predictions, we thought we had to search a much bigger volume of space to find such galaxies," said Castellano.

"These observations just make your head explode. This is a whole new chapter in astronomy. It's like an archaeological dig, and suddenly you find a lost city or something you didn't know about. It's just staggering," added Paola Santini, fourth author of the Castellano et al. GLASS-JWST paper.

"While the distances of these early sources still need to be confirmed with spectroscopy, their extreme brightnesses are a real puzzle, challenging our understanding of galaxy formation," noted Pascal Oesch at the University of Geneva in Switzerland, second author of the Naidu et al. paper.

The Webb observations nudge astronomers toward a consensus that an unusual number of galaxies in the early universe were much brighter than expected. This will make it easier for Webb to find even more early galaxies in subsequent deep sky surveys, say researchers.

"We've nailed something that is incredibly fascinating. These galaxies would have had to have started coming together maybe just 100 million years after the big bang. Nobody expected that the dark ages would have ended so early," said Garth Illingworth of the University of California at Santa Cruz, a member of the Naidu/Oesch team. "The primal universe would have been just one hundredth its current age. It's a sliver of time in the 13.8 billion-year-old evolving cosmos."

Erica Nelson of the University of Colorado, a member of the Naidu/Oesch team, noted that "our team was struck by being able to measure the shapes of these first galaxies; their calm, orderly disks question our understanding of how the first galaxies formed in the crowded, chaotic early universe." This remarkable discovery of compact disks at such early times was only possible because of Webb's much sharper images, in infrared light, compared to Hubble.

"These galaxies are very different than the Milky Way or other big galaxies we see around us today," said Treu.

Illingworth emphasized the two bright galaxies found by these teams have a lot of light. He said one option is that they could have been very massive, with lots of low-mass stars, like later galaxies. Alternatively, they could be much less massive, consisting of far fewer extraordinarily bright stars, known as Population III stars. Long theorized, they would be the first stars ever born, blazing at blistering temperatures and made up only of primordial hydrogen and helium -- before stars could later cook up heavier elements in their nuclear fusion furnaces. No such extremely hot, primordial stars are seen in the local universe.

"Indeed, the farthest source is very compact, and its colors seem to indicate that its stellar population is particularly devoid of heavy elements and could even contain some Population III stars. Only Webb spectra will tell," said Adriano Fontana, second author of the Castellano et al. paper and a member of the GLASS-JWST team.

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