Dark matter could have helped make supermassive black holes in the early universe

Supermassive black holes typically take billions of years to form. But the James Webb Space Telescope is finding them not that long after the Big Bang -- before they should have had time to form.

It takes a long time for supermassive black holes, like the one at the center of our Milky Way galaxy, to form. Typically, the birth of a black hole requires a giant star with the mass of at least 50 of our suns to burn out -- a process that can take a billion years -- and its core to collapse in on itself.

Even so, at only about 10 solar masses, the resulting black hole is a far cry from the 4 million-solar-masses black hole, Sagittarius A*, found in our Milky Way galaxy, or the billion-solar-mass supermassive black holes found in other galaxies. Such gigantic black holes can form from smaller black holes by accretion of gas and stars, and by mergers with other black holes, which take billions of years.

Why, then, is the James Webb Space Telescope discovering supermassive black holes near the beginning of time itself, eons before they should have been able to form? UCLA astrophysicists have an answer as mysterious as the black holes themselves: Dark matter kept hydrogen from cooling long enough for gravity to condense it into clouds big and dense enough to turn into black holes instead of stars. The finding is published in the journal Physical Review Letters.

"How surprising it has been to find a supermassive black hole with a billion solar mass when the universe itself is only half a billion years old," said senior author Alexander Kusenko, a professor of physics and astronomy at UCLA. "It's like finding a modern car among dinosaur bones and wondering who built that car in the prehistoric times."

Some astrophysicists have posited that a large cloud of gas could collapse to make a supermassive black hole directly, bypassing the long history of stellar burning, accretion and mergers. But there's a catch: Gravity will, indeed, pull a large cloud of gas together, but not into one large cloud. Instead, it gathers sections of the gas into little halos that float near each other but don't form a black hole.

The reason is because the gas cloud cools too quickly. As long as the gas is hot, its pressure can counter gravity. However, if the gas cools, pressure decreases, and gravity can prevail in many small regions, which collapse into dense objects before gravity has a chance to pull the entire cloud into a single black hole.

"How quickly the gas cools has a lot to do with the amount of molecular hydrogen," said first author and doctoral student Yifan Lu. "Hydrogen atoms bonded together in a molecule dissipate energy when they encounter a loose hydrogen atom. The hydrogen molecules become cooling agents as they absorb thermal energy and radiate it away. Hydrogen clouds in the early universe had too much molecular hydrogen, and the gas cooled quickly and formed small halos instead of large clouds."

Lu and postdoctoral researcher Zachary Picker wrote code to calculate all possible processes of this scenario and discovered that additional radiation can heat the gas and dissociate the hydrogen molecules, altering how the gas cools.

"If you add radiation in a certain energy range, it destroys molecular hydrogen and creates conditions that prevent fragmentation of large clouds," Lu said.

But where does the radiation come from?

Only a very tiny portion of matter in the universe is the kind that makes up our bodies, our planet, the stars and everything else we can observe. The vast majority of matter, detected by its gravitational effects on stellar objects and by the bending of light rays from distant sources, is made of some new particles, which scientists have not yet identified.

The forms and properties of dark matter are therefore a mystery that remains to be solved. While we don't know what dark matter is, particle theorists have long speculated that it could contain unstable particles which can decay into photons, the particles of light. Including such dark matter in the simulations provided the radiation needed for the gas to remain in a large cloud while it is collapsing into a black hole.

Dark matter could be made of particles that slowly decay, or it could be made of more than one particle species: some stable and some that decay at early times. In either case, the product of decay could be radiation in the form of photons, which break up molecular hydrogen and prevent hydrogen clouds from cooling too quickly. Even very mild decay of dark matter yielded enough radiation to prevent cooling, forming large clouds and, eventually, supermassive black holes.

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The rotation of a nearby star stuns astronomers

Astronomers from the University of Helsinki have found that the rotational profile of a nearby star, V889 Herculis, differs considerably from that of the Sun. The observation provides insights into the fundamental stellar strophysics and helps understanding the activity of the Sun, its spot structures and eruptions.

The Sun rotates the fastest at the equator, whereas the rotation rate slows down at higher latitudes and is the slowest as the polar regions. But a nearby Sun-like star V889 Herculis, some 115 light years away in the constellation of Hercules, rotates the fastest at a latitude of about 40 degrees, while both the equator and polar regions rotate more slowly.

Similar rotational profile has not been observed for any other star. The result is stunning because stellar rotation has been considered a well-understood fundamental physical parameter but such a rotational profile has not been predicted even in computer simulations.

"We applied a newly developed statistical technique to the data of a familiar star that has been studied in the University of Helsinki for years. We did not expect to see such anomalies in stellar rotation. The anomalies in the rotational profile of V889 Herculis indicate that our understanding of stellar dynamics and magnetic dynamos are insufficient, "explains researcher Mikko Tuomi who coordinated the research

Dynamics of a ball of plasma

The target star V889 Herculis is much like a young Sun, telling a story about the history and evolution of the Sun. Tuomi emphasises that it is crucial to understand stellar astrophysics in order to, for instance, predict activity-induced phenomena on the Solar surface, such as spots and eruptions.

Stars are spherical structures where matter is in the state of plasma, consisting of charged particles. They are dynamical objects that hang in a balance between the pressure generated in nuclear reactions in their cores and their own gravity. They have no solid surfaces unlike many planets.

The stellar rotation is not constant for all latitudes -- an effect known as differential rotation. It is caused by the fact that hot plasma rises to the star's surface via a phenomenon called convection, which in turn has an effect on the local rotation rate. This is because angular momentum must be conserved and the convection occurs perpendicular to the rotational axis near equator whereas it is parallel to the axis near the poles.

However, many factors such as stellar mass, age, chemical composition, rotation period, and magnetic field have effects on the rotation and give rise to variations in the differential rotation profiles.

A statistical method for determining rotational profile

Thomas Hackman, docent of astronomy, who participated in the research, explains that the Sun has been the only star for which studying the rotational profile has been possible.

"Stellar differential rotation is a very crucial factor that has an effect on the magnetic activity of stars. The method we have developed opens a new window into the inner workings of other stars.

"The astronomers at the Department of Particle Physics and Astrophysics of the Helsinki University have determined the rotational profile of two nearby young stars by applying a new statistical modelling to long-baseline brightness observations. They modelled the periodic variations in the observations by accounting for the differences in the apparent spot movement at different latitudes. The spot movement then enabled estimating the rotational profile of the stars.

"The second one of the targets stars, LQ Hydrae in the constellation of Hydra, was found to be rotating much like a rigid body -- the rotation appeared unchanged from the equator to the poles, which indicates that the differences are very small."

Observations from the Fairborne Observatory

The researchers base their results on the observations of the target stars from the Fairborn observatory. The brightnesses of the stars have been monitored with robotic telescopes for around 30 years, which provides insights into the behaviour of the stars over a long period of time.

Tuomi appreciates the work of senior astronomer Gregory Henry, of Tennessee University, United States, who leads the Fairborne observational campaign.

"For many years, Greg's project has been extremely valuable in understanding the behaviour of nearby stars. Whether the motivation is to study the rotation and properties of young, active stars or to understand the nature of stars with planets, the observations from Fairborn Observatory have been absolutely crucial. It is amazing that even in the era of great space-based observatories we can obtain fundamental information on the stellar astrophysics with small 40cm ground-based telescopes.

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Astrophysicists uncover supermassive blackhole/dark matter connection in solving the 'final parsec problem'

Researchers have found a link between some of the largest and smallest objects in the cosmos: supermassive black holes and dark matter particles.

Their new calculations reveal that pairs of supermassive black holes (SMBHs) can merge into a single larger black hole because of previously overlooked behaviour of dark matter particles, proposing a solution to the longstanding "final parsec problem" in astronomy.

The research is described in Self-interacting dark matter solves the final parsec problem of supermassive black hole mergers published this month in the journal Physical Review Letters.

In 2023, astrophysicists announced the detection of a "hum" of gravitational waves permeating the universe. They hypothesized that this background signal emanated from millions of merging pairs of SMBHs each billions of times more massive than our Sun.

However, theoretical simulations showed that as pairs of these mammoth celestial objects spiral closer together, their approach stalls when they are roughly a parsec apart -- a distance of about three light years -- thereby preventing a merger.

Not only did this "final parsec problem" conflict with the theory that merging SMBHs were the source of the gravitational wave background, it was also at odds with the theory that SMBHs grow from the merger of less massive black holes.

"We show that including the previously overlooked effect of dark matter can help supermassive black holes overcome this final parsec of separation and coalesce," says paper co-author Gonzalo Alonso-Álvarez, a postdoctoral fellow in the Department of Physics at the University of Toronto and the Department of Physics and Trottier Space Institute at McGill University. "Our calculations explain how that can occur, in contrast to what was previously thought."

The paper's co-authors include Professor James Cline from McGill University and the CERN Theoretical Physics Department in Switzerland and Caitlyn Dewar, a master of science student in physics at McGill.

SMBHs are thought to lie in the centres of most galaxies and when two galaxies collide, the SMBHs fall into orbit around each other. As they revolve around each other, the gravitational pull of nearby stars tugs at them and slows them down. As a result, the SMBHs spiral inward toward a merger.

Previous merger models showed that when the SMBHs approached to within roughly a parsec, they begin to interact with the dark matter cloud or halo in which they are embedded. They indicated that the gravity of the spiraling SMBHs throws dark matter particles clear of the system and the resulting sparsity of dark matter means that energy is not drawn from the pair and their mutual orbits no longer shrink.

While those models dismissed the impact of dark matter on the SMBH's orbits, the new model from Alonso-Álvarez and his colleagues reveals that dark matter particles interact with each other in such a way that they are not dispersed. The density of the dark matter halo remains high enough that interactions between the particles and the SMBHs continue to degrade the SMBH's orbits, clearing a path to a merger.

"The possibility that dark matter particles interact with each other is an assumption that we made, an extra ingredient that not all dark matter models contain," says Alonso-Álvarez. "Our argument is that only models with that ingredient can solve the final parsec problem."

The background hum generated by these colossal cosmic collisions is made up of gravitational waves of much longer wavelength than those first detected in 2015 by astrophysicists operating the Laser Interferometer Gravitational-Wave Observatory (LIGO). Those gravitational waves were generated by the merger of two black holes, both some 30 times the mass of the Sun.

The background hum has been detected in recent years by scientists operating the Pulsar Timing Array. The array reveals gravitational waves by measuring minute variations in signals from pulsars, rapidly rotating neutron stars that emit strong radio pulses.

"A prediction of our proposal is that the spectrum of gravitational waves observed by pulsar timing arrays should be softened at low frequencies," says Cline. "The current data already hint at this behavior, and new data may be able to confirm it in the next few years."

In addition to providing insight into SBMH mergers and the gravitational wave background signal, the new result also provides a window into the nature of dark matter.

"Our work is a new way to help us understand the particle nature of dark matter," says Alonso-Álvarez. "We found that the evolution of black hole orbits is very sensitive to the microphysics of dark matter and that means we can use observations of supermassive black hole mergers to better understand these particles."

For example, the researchers found that the interactions between dark matter particles they modeled also explains the shapes of galactic dark matter halos.

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Researchers advance detection of gravitational waves to study collisions of neutron stars and black holes

Researchers at the University of Minnesota Twin Cities College of Science and Engineering co-led a new study by an international team that will improve the detection of gravitational waves -- ripples in space and time.

The research aims to send alerts to astronomers and astrophysicists within 30 seconds after the detection, helping to improve the understanding of neutron stars and black holes and how heavy elements, including gold and uranium, are produced.

The findings were recently published in the Proceedings of the National Academy of Sciences (PNAS).

Gravitational waves interact with spacetime by compressing it in one direction while stretching it in the perpendicular direction. That is why current state-of-the-art gravitational wave detectors are L-shaped and measure the relative lengths of the laser using interferometry, a measurement method which looks at the interference patterns produced by the combination of two light sources. Detecting gravitational waves requires measuring the length of the laser to precise measurements: equivalent to measuring the distance to the nearest star, around four light years away, down to the width of a human hair.

This research is part of the LIGO-Virgo-KAGRA (LVK) Collaboration, a network of gravitational wave interferometers across the world.

In the latest simulation campaign, data was used from previous observation periods and simulated gravitational wave signals were added to show the performance of the software and equipment upgrades. The software can detect the shape of signals, track how the signal behaves, and estimate what masses are included in the event, like neutron stars or black holes. Neutron stars are the smallest, most dense stars known to exist and are formed when massive stars explode in supernovas.

Once this software detects a gravitational wave signal, it sends out alerts to subscribers, which usually include astronomers or astrophysicists, to communicate where the signal was located in the sky. With the upgrades in this observing period, scientists are able to send alerts faster, under 30 seconds, after the detection of a gravitational wave.

"With this software, we can detect the gravitational wave from neutron star collisions that is normally too faint to see unless we know exactly where to look," said Andrew Toivonen, a Ph.D. student in the University of Minnesota Twin Cities School of Physics and Astronomy. "Detecting the gravitational waves first will help locate the collision and help astronomers and astrophysicists to complete further research."

Astronomers and astrophysicists could use this information to understand how neutron stars behave, study nuclear reactions between neutron stars and black holes colliding, and how heavy elements, including gold and uranium, are produced.

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No gamma rays seen coming from nearby supernova

A nearby supernova in 2023 offered astrophysicists an excellent opportunity to test ideas about how these types of explosions boost particles, called cosmic rays, to near light-speed. But surprisingly, NASA's Fermi Gamma-ray Space Telescope detected none of the high-energy gamma-ray light those particles should produce.

On May 18, 2023, a supernova erupted in the nearby Pinwheel galaxy (Messier 101), located about 22 million light-years away in the constellation Ursa Major. The event, named SN 2023ixf, is the most luminous nearby supernova discovered since Fermi launched in 2008.

"Astrophysicists previously estimated that supernovae convert about 10% of their total energy into cosmic ray acceleration," said Guillem Martí-Devesa, a researcher at the University of Trieste in Italy. "But we have never observed this process directly. With the new observations of SN 2023ixf, our calculations result in an energy conversion as low as 1% within a few days after the explosion. This doesn't rule out supernovae as cosmic ray factories, but it does mean we have more to learn about their production."

The paper, led by Martí-Devesa while at the University of Innsbruck in Austria, will appear in a future edition of Astronomy and Astrophysics.

Trillions of trillions of cosmic rays collide with Earth's atmosphere every day. Roughly 90% of them are hydrogen nuclei -- or protons -- and the remainder are electrons or the nuclei of heavier elements.

Scientists have been investigating cosmic ray origins since the early 1900s, but the particles can't be traced back to their sources. Because they're electrically charged, cosmic rays change course as they travel to Earth thanks to magnetic fields they encounter.

"Gamma rays, however, travel directly to us," said Elizabeth Hays, the Fermi project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Cosmic rays produce gamma rays when they interact with matter in their environment. Fermi is the most sensitive gamma-ray telescope in orbit, so when it doesn't detect an expected signal, scientists must explain the absence. Solving that mystery will build a more accurate picture of cosmic ray origins."

Astrophysicists have long suspected supernovae of being top cosmic ray contributors.

These explosions occur when a star at least eight times the Sun's mass runs out of fuel. The core collapses and then rebounds, propelling a shock wave outward through the star. The shock wave accelerates particles, creating cosmic rays. When cosmic rays collide with other matter and light surrounding the star, they generate gamma rays.

Supernovae greatly impact a galaxy's interstellar environment. Their blast waves and expanding cloud of debris may persist for more than 50,000 years. In 2013, Fermi measurements showed that supernova remnants in our own Milky Way galaxy were accelerating cosmic rays, which generated gamma-ray light when they struck interstellar matter. But astronomers say the remnants aren't producing enough high-energy particles to match scientists' measurements on Earth.

One theory proposes that supernovae may accelerate the most energetic cosmic rays in our galaxy in the first few days and weeks after the initial explosion.

But supernovae are rare, occurring only a few times a century in a galaxy like the Milky Way. Out to distances of around 32 million light-years, a supernova occurs, on average, just once a year.

After a month of observations, starting when visible light telescopes first saw SN 2023ixf, Fermi had not detected gamma rays.

"Unfortunately, seeing no gamma rays doesn't mean there are no cosmic rays," said co-author Matthieu Renaud, an astrophysicist at the Montpellier Universe and Particles Laboratory, part of the National Center for Scientific Research in France. "We have to go through all the underlying hypotheses regarding acceleration mechanisms and environmental conditions in order to convert the absence of gamma rays into an upper limit for cosmic ray production."

The researchers propose a few scenarios that may have affected Fermi's ability to see gamma rays from the event, like the way the explosion distributed debris and the density of material surrounding the star.

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The hidden role of the Milky Way in ancient Egyptian mythology

Ancient Egyptians were known for their religious beliefs and astronomical knowledge of the Sun, Moon, and planets, but up until now it has been unclear what role the Milky Way played in Egyptian religion and culture.

A new study by a University of Portsmouth astrophysicist sheds light on the relationship between the Milky Way and the Egyptian sky-goddess Nut.

Nut is goddess of the sky, who is often depicted as a star-studded woman arched over her brother, the earth god Geb.

She protects the earth from being flooded by the encroaching waters of the void, and plays a key role in the solar cycle, swallowing the Sun as it sets at dusk and giving birth to it once more as it rises at dawn.

The paper draws on ancient Egyptian texts and simulations to argue that the Milky Way might have shone a spotlight, as it were, on Nut's role as the sky.

It proposes that in winter, the Milky Way highlighted Nut's outstretched arms, while in summer, it traced her backbone across the heavens.

Associate Professor in Astrophysics, Dr Or Graur, said: "I chanced upon the sky-goddess Nut when I was writing a book on galaxies and looking into the mythology of the Milky Way. I took my daughters to a museum and they were enchanted by this image of an arched woman and kept asking to hear stories about her.

"This sparked my interest and I decided to combine both astronomy and Egyptology to do a double analysis -- astronomical and cross-cultural -- of the sky-goddess Nut, and whether she really could be linked to the Milky Way."

Dr Graur drew from a rich collection of ancient sources including the Pyramid Texts, Coffin Texts, and the Book of Nut and compared them alongside sophisticated simulations of the Egyptian night sky.

He found compelling evidence that the Milky Way highlighted Nut's divine presence.

Furthermore, Dr Graur connected Egyptian beliefs with those of other cultures, showing similarities in how different societies interpret the Milky Way.

He said: "My study also shows that Nut's role in the transition of the deceased to the afterlife and her connection to the annual bird migration are consistent with how other cultures understand the Milky Way. For example, as a spirits' road among different peoples in North and Central America or as the Birds' Path in Finland and the Baltics.

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Tiniest 'starquake' ever detected

An orange dwarf star has yielded the tiniest 'starquakes' ever recorded, measured by an international team of scientists.

Named Epsilon Indi, the star is the smallest and coolest dwarf star yet observed with solar-like oscillations -- "starquakes" like those shown by the Sun.

These oscillations provide indirect glimpses of stellar interiors -- just as earthquakes tell us about Earth's interior -- and so are important sources of information about the makeup of the star.

The measurements were taken by an international team, led by the Institute of Astrophysics and Space Sciences in Portugal, and including researchers from the University of Birmingham.

The study is published in Astronomy and Astrophysics Letters.

The quakes were detected using a technique dubbed asteroseismology, which measures oscillations in stars.

Using the ESPRESSO spectrograph, mounted at the European Southern Observatory's (ESO) Very Large Telescope (VLT), the team was able to record the oscillations with unprecedented precision.

Lead author Tiago Campante, of the Institute of Astrophysics and Space Sciences at the University of Porto, said: "The extreme precision level of these observations is an outstanding technological achievement. Importantly, this detection conclusively shows that precise asteroseismology is possible down to cool dwarfs with surface temperatures as low as 4200 degrees Celsius, about 1000 degrees cooler than the Sun's surface, effectively opening up a new domain in observational astrophysics."

Orange dwarf stars have recently become a focus in the search for habitable planets and extraterrestrial life.

Professor Bill Chaplin, Head of the School of Physics & Astronomy at Birmingham, and a member of the team, said: "The mismatch between the predicted and observed sizes of these stars has implications for finding planets around them. If we use the most successful planet-finding technique -- the so-called transit method -- we get the size of the planet relative to the size of the star; if we don't size-up the star correctly, the same will be true of any small planet we have found." The detection of oscillations will help to understand and minimise these discrepancies, and improve the theoretical models of stars.

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Astrophysicist's research could provide a hint in the search for dark matter

Dark matter is one of science's greatest mysteries. Although it is believed to make up about 85 percent of the cosmos, scientists know very little about its fundamental nature. Research by Clemson University postdoctoral fellow Alex McDaniel provides some of the most stringent constraints on the nature of dark matter yet. It also revealed a small hint of a signal that, if real, could be confirmed in the next decade or so.

Dark matter is one of science's greatest mysteries.

It doesn't absorb, reflect or emit light, so we can't see it. But its presence is implied by the gravitational effects it appears to have on galaxies.

Although dark matter makes up about 85 percent of the cosmos, scientists know very little about its fundamental nature.

Theories abound, and research by Clemson University postdoctoral fellow Alex McDaniel provides some of the most stringent constraints on the nature of dark matter yet.

His research also reveals a small hint of a signal that, if real, could be confirmed sometime in the next decade or so.

"With data collection and new discoveries in the future, this small hint could potentially turn into a very concrete detection of a dark matter model," McDaniel said.

Detecting dark matter would be groundbreaking.

"Dark matter is one of the most important things in astrophysics, and we know next to nothing about it. Discovering it will be a tremendous breakthrough," said Marco Ajello, an associate professor in the Clemson Department of Physics and Astronomy and McDaniel's adviser.

"Whoever discovers may win a Nobel Prize. It's that big."

In this work, McDaniel and collaborators were searching dwarf galaxies for dark matter that self-annihilates into ordinary matter and gamma rays, a form of light at the highest energy levels.

Dwarf galaxies are ideal for study because they are small, rich in dark matter and mostly lack other astrophysics phenomena such as gas, dust and supernova that could contaminate the findings.

"We look for these because, ideally, they give us a clean signal or allow us to rule out certain particle theories," McDaniel said.

Some models predict that dark matter has a certain mass or cross section, which is the probability of a specific event occurring due to the interaction of particles.

That would determine what researchers would expect to see in gamma rays.

If they don't see that, they can rule out those masses and cross sections, he said.

"In this paper, we do more ruling out, saying that dark matter can't have those masses or cross section," said Chris Karwin, a former postdoc at Clemson and a co-author of the study.

Karwin is now a postdoctoral fellow at the NASA Goddard Space Flight Center.

"But compared to previous studies, we do start to see a hint of something that might be a signal from these systems."

McDaniel's study uses the larger samples that include additional discovered dwarf galaxies and larger amounts of data than previous studies.

He included about 50 dwarf galaxies in his study but said that with new, more powerful telescopes coming online in the near future, he expects that number to increase to 150-200.

"The new telescopes are basically dwarf galaxy detectors," he said.

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Astrophysicists crack the case of 'disappearing' Sulphur in planetary nebulae

Two astrophysicists from the Laboratory for Space Research (LSR) at The University of Hong Kong (HKU) have finally solved a 20-year-old astrophysical puzzle concerning the lower-than-expected amounts of the element Sulphur found in Planetary Nebulae (PNe) in comparison to expectations and measurements of other elements and other types of astrophysical objects.

The expected levels of Sulphur have long appeared to be "missing in action." However, they have now finally reported for duty after hiding in plain sight, as a result of leveraging highly accurate and reliable data.

The team has recently reported their findings in Astrophysical Journal Letters.

Background

PNe are the short-lived glowing, ejected, gaseous shrouds of dying stars that have long fascinated and enthused professional and amateur astronomers alike with their colourful and varied shapes.

PNe live for only a few tens of thousands of years compared to their host stars, which can take billions of years before they pass through the PN phase on the way to becoming "white dwarfs." Consequently, PNe provide an almost instantaneous snapshot of stellar death throes.

They are a vital, scientific window into late-stage stellar evolution as their rich emission line spectra enable detailed studies of their chemical compositions.

The Enigmatic Sulphur Anomaly

Past studies showed that PNe optical spectra appeared to have a varying deficit of the element Sulphur.

This deficit was difficult to explain because Sulphur, known as an "α element," should be produced in lockstep with other elements like oxygen, neon, argon and chlorine in more massive stars.

As a result, its cosmic abundance should also be directly proportional.

Surprisingly, while strong correlations between Sulphur and Oxygen abundances have been observed in H II regions (Hydrogen ionised region) and blue compact galaxies, PNe originating from low- to intermediate-mass stars consistently exhibit lower Sulfur levels, giving rise to the so-called mysterious "sulfur anomaly" that has perplexed and annoyed astronomers for decades.

Our Work Solving the Mystery

Ms Shuyu TAN, a graduate of HKU MPhil in Physics and Research Assistant at HKU LSR, along with her supervisor Professor Quentin PARKER, the Director of LSR, utilised an unprecedented sample of exceptional high signal to noise (S/N) optical spectra for approximately 130 PNe located in the centre of our Galaxy.

This exceptional dataset had minimal background noise, allowing for a clear and detailed examination of the spectral features, helping the team effectively tackle and solve the mystery.

These PNe were observed using the world-leading European Southern Observatory (ESO) 8m Very Large Telescope in Chile.

It turns out the anomaly was essentially a result of poor data quality for Sulphur emission lines in PNe spectra.

It was found that using Oxygen as the base metallicity comparator to other elements was not accurate, and instead, Argon demonstrated a stronger correlation with Oxygen for Sulphur and has been suggested as a more reliable indicator of metallicity and a suitable comparison element.

So, when a large, carefully selected sample of PNe are spectroscopically observed at high S/N on a large telescope, not only did the data reveal a strong "lock-step" behaviour or Sulphur in PNe for the first time, as seen and expected for other types of astrophysical objects, but the anomaly itself effectively went away.

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Is oxygen the cosmic key to alien technology?

In the quest to understand the potential for life beyond Earth, researchers are widening their search to encompass not only biological markers, but also technological ones. While astrobiologists have long recognized the importance of oxygen for life as we know it, oxygen could also be a key to unlocking advanced technology on a planetary scale.

In a new study published in Nature Astronomy, Adam Frank, the Helen F. and Fred H. Gowen Professor of Physics and Astronomy at the University of Rochester and the author of The Little Book of Aliens (Harper, 2023), and Amedeo Balbi, an associate professor of astronomy and astrophysics at the University of Roma Tor Vergata, Italy, outline the links between atmospheric oxygen and the potential rise of advanced technology on distant planets.

"We are ready to find signatures of life on alien worlds," Frank says.

"But how do the conditions on a planet tell us about the possibilities for intelligent, technology-producing life?"

"In our paper, we explore whether any atmospheric composition would be compatible with the presence of advanced technology," Balbi says.

"We found that the atmospheric requirements may be quite stringent."

Igniting cosmic technospheres

Frank and Balbi posit that, beyond its necessity for respiration and metabolism in multicellular organisms, oxygen is crucial to developing fire -- and fire is a hallmark of a technological civilization.

They delve into the concept of "technospheres," expansive realms of advanced technology that emit telltale signs -- called "technosignatures" -- of extraterrestrial intelligence.

On Earth, the development of technology demanded easy access to open-air combustion -- the process at the heart of fire, in which something is burned by combining a fuel and an oxidant, usually oxygen.

Whether it's cooking, forging metals for structures, crafting materials for homes, or harnessing energy through burning fuels, combustion has been the driving force behind industrial societies.

Tracing back through Earth's history, the researchers found that the controlled use of fire and the subsequent metallurgical advancements were only possible when oxygen levels in the atmosphere reached or exceeded 18 percent.

This means that only planets with significant oxygen concentrations will be capable of developing advanced technospheres, and, therefore, leaving detectable technosignatures.

The oxygen bottleneck

The levels of oxygen required to biologically sustain complex life and intelligence are not as high as the levels necessary for technology, so while a species might be able to emerge in a world without oxygen, it will not be able to become a technological species, according to the researchers.

"You might be able to get biology -- you might even be able to get intelligent creatures -- in a world that doesn't have oxygen," Frank says, "but without a ready source of fire, you're never going to develop higher technology because higher technology requires fuel and melting."

Enter the "oxygen bottleneck," a term coined by the researchers to describe the critical threshold that separates worlds capable of fostering technological civilizations from those that fall short.

That is, oxygen levels are a bottleneck that impedes the emergence of advanced technology.

"The presence of high degrees of oxygen in the atmosphere is like a bottleneck you have to get through in order to have a technological species," Frank says.

"You can have everything else work out, but if you don't have oxygen in the atmosphere, you're not going to have a technological species."

Targeting extraterrestrial hotspots

The research, which addresses a previously unexplored facet in the cosmic pursuit of intelligent life, underscores the need to prioritize planets with high oxygen levels when searching for extraterrestrial technosignatures.

"Targeting planets with high oxygen levels should be prioritized because the presence or absence of high oxygen levels in exoplanet atmospheres could be a major clue in finding potential technosignatures," Frank says.

"The implications of discovering intelligent, technological life on another planet would be huge," adds Balbi.

"Therefore, we need to be extremely cautious in interpreting possible detections. Our study suggests that we should be skeptical of potential technosignatures from a planet with insufficient atmospheric oxygen."

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Reaching for the (invisible) stars

Supernovae-stellar explosions as bright as an entire galaxy-have fascinated us since time immemorial. Yet, there are more hydrogen-poor supernovae than astrophysicists can explain. Now, a new Assistant Professor at the Institute of Science and Technology Austria (ISTA) has played a pivotal role in identifying the missing precursor star population. The results, now published in Science, go back to a conversation the involved professors had many years ago as junior scientists.

Some stars do not simply die down, but explode in a stellar blast that could outshine entire galaxies. These cosmic phenomena, called supernovae, spread light, elements, energy, and radiation in space and send galactic shock waves that could compress gas clouds and generate new stars. In other words, supernovae shape our universe. Among these, hydrogen-poor supernovae from exploding massive stars have long puzzled astrophysicists. The reason: scientists have not been able to put their finger on their precursor stars. It is almost as if these supernovae appeared out of nowhere.

"There are many more hydrogen-poor supernovae than our current models can explain. Either we can't detect the stars that mature on this path, or we must revise all our models," says ISTA Assistant Professor Ylva Götberg. She pioneered this work together with Maria Drout, an Associated Faculty Member of the Dunlap Institute for Astronomy & Astrophysics, University of Toronto, Canada. "Single stars would typically explode as hydrogen-rich supernovae. Being hydrogen-poor indicates that the precursor star must have lost its thick hydrogen-rich envelope. This happens naturally in a third of all massive stars through envelope stripping by a binary companion star," says Götberg. Now, Götberg and Drout combined their areas of expertise in theoretical modeling and observation to hunt down the missing stars. Their quest is successful: they document a first-of-its-kind star population that finally bridges a large knowledge gap and sheds light on the origin of hydrogen-poor supernovae.

Binary stars and envelope stripping

The stars that Götberg and Drout search for go in pairs: interlocked in a binary star system. Some binary systems are well-known to us Earthlings: these include the brightest star in our night sky, Sirius A, and its faint companion star Sirius B. The Sirius binary system is located only 8.6 light-years away from Earth-a stone's throw in cosmic terms. This explains Sirius A's observed brightness in our night sky.

Astrophysicists expect the missing stars to be initially formed from massive binary systems. In a binary system, the stars would orbit around one another until the more massive star's thick, hydrogen-rich envelope expands. Eventually, the expanding envelope experiences a stronger gravitational pull to the companion star than to its own core. This causes a transfer of mass to begin, which eventually leads the entire hydrogen-rich envelope to be stripped off, leaving the hot and compact helium core exposed-more than 10 times hotter than the Sun's surface. This is precisely the type of stars that Götberg and Drout are looking for. "Intermediate mass helium stars stripped through binary interaction are predicted to play important roles in astrophysics. Yet, they were not observed until now," says Götberg. In fact, there is an important mass gap between the known classes of helium stars: the more massive Wolf-Rayet (WR) stars have more than 10 times the Sun's mass, and the low-mass subdwarf stars could have around half the Sun's mass. However, models have predicted the precursors of hydrogen-poor supernovae to lie between 2 and 8 solar masses following stripping.

Not just a needle in the haystack

Before Götberg and Drout's study, only one star was found to fulfill the expected mass and composition criteria and was called "Quasi-WR" (or "Almost Wolf-Rayet"). "Yet, the stars that follow this path have such a long lifetime that many must be scattered all over the observable universe," says Götberg. Did the scientists simply not "see" them? Thus, Götberg and Drout drew on their complementary expertise. With the help of UV photometry and optical spectroscopy, they identified a population of 25 stars that are consistent with the expectations for intermediate-mass helium stars. The stars are located in two well-studied neighboring galaxies, the Large and the Small Magellanic Clouds. "We showed that these stars were bluer than the stellar birthline, the bluest phase in a single star's lifetime. Single stars mature by evolving towards the redder region of the spectrum. A star only shifts in the opposite direction if its outer layers are removed-something that is expected to be common in interacting binary stars and rare among single massive stars," explains Götberg.

The scientists then verified their candidate star population using optical spectroscopy: they showed that the stars had strong spectral signatures of ionized helium. "Strong ionized helium lines tell us two important things: first, they confirm that the stars' outermost layers are dominated by helium and, second, that their surface is very hot. This is what happens to stars left as an exposed, compact, helium-rich core following stripping," says Götberg. Yet, both stars in a binary system contribute to the observed spectra. Thus, this technique allowed the researchers to classify their candidate population depending on which star contributed the most to the spectrum. "This work allowed us to find the missing population of intermediate-mass, stripped helium stars, the predicted progenitors of hydrogen-poor supernovae. These stars have always been there and there are probably many more out there. We must simply come up with ways to find them," says Götberg. "Our work may be one of the first attempts, but there should be other ways possible."

From graduate students at a conference to group leaders

The idea behind this project sparked in a discussion following a talk by Götberg at a conference that she and Drout attended during their graduate studies. Both scientists, then Early Career Researchers reaching for the stars, are now group leaders in their field. Götberg joined ISTA in September following her research at the Carnegie Observatories in Pasadena, California, as a NASA Hubble postdoctoral fellow. At ISTA, Götberg joins the Institute's growing ranks of young group leaders in astrophysics and leads her own group focused on studying the binary interactions of stars.

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Unlocking neutron star rotation anomalies: Insights from quantum simulation

A collaboration between quantum physicists and astrophysicists, led by Francesca Ferlaino and Massimo Mannarelli, has achieved a significant breakthrough in understanding neutron star glitches. They were able to numerically simulate this enigmatic cosmic phenomenon with ultracold dipolar atoms. This research establishes a strong link between quantum mechanics and astrophysics and paves the way for quantum simulation of stellar objects from Earth.

Neutron stars have fascinated and puzzled scientists since the first detected signature in 1967.

Known for their periodic flashes of light and rapid rotation, neutron stars are among the densest objects in the universe, with a mass comparable to that of the Sun but compressed into a sphere only about 20 kilometers in diameter.

These stellar objects exhibit a peculiar behavior known as a "glitch," where the star suddenly speeds up its spin.

This phenomenon suggests that neutron stars might be partly superfluid.

In a superfluid, rotation is characterized by numerous tiny vortices, each carrying a fraction of angular momentum.

A glitch occurs when these vortices escape from the star's inner crust to its solid outer crust, thereby increasing the star's rotational speed.

The key ingredient for this study lies in the concept of a "supersolid" -- a state that exhibits both crystalline and superfluid properties -- which is predicted to be a necessary ingredient of neutron star glitches.

Quantized vortices nest within the supersolid until they collectively escape and are consequently absorbed by the outer crust of the star, accelerating its rotation.

Recently, the supersolid phase has been realized in experiments with ultracold dipolar atoms, providing a unique opportunity to simulate the conditions within a neutron star.

The recent study by researchers at the University of Innsbruck and the Austrian Academy of Sciences as well as the Laboratori Nazionali del Gran Sasso and the Gran Sasso Science Institute in Italy demonstrates that glitches can occur in ultracold supersolids, serving as versatile analogues for the inside of neutron stars.

This groundbreaking approach allows for a detailed exploration of the glitch mechanism, including its dependence on the quality of the supersolid.

"Our research establishes a strong link between quantum mechanics and astrophysics and provides a new perspective on the inner nature of neutron stars," says first author Elena Poli.

Glitches provide valuable insights into the internal structure and dynamics of neutron stars.

By studying these events, scientists can learn more about the properties of matter under extreme conditions.

"This research shows a new approach to gain insights into the behavior of neutron stars and opens new avenues for the quantum simulation of stellar objects from low-energy Earth laboratories," emphasizes Francesca Ferlaino.

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Astronomers determine the age of three mysterious baby stars at the heart of the Milky Way

Through analysis of high-resolution data from a ten-metre telescope in Hawaii, researchers at Lund University in Sweden have succeeded in generating new knowledge about three stars at the very heart of the Milky Way. The stars proved to be unusually young with a puzzling chemical composition that surprised the researchers.

The study, which has been published in The Astrophysical Journal Letters, examined a group of stars located in the nuclear star cluster that makes up the heart of the galaxy.

It concerns three stars that are difficult to study because they are extremely far away from our solar system, and hidden behind enormous clouds of dust and gas that block out light.

The fact that the area is also full of stars makes it very complicated to discern individual stars.

In a previous study, the researchers put forward a hypothesis that these specific stars in the middle of the Milky Way could be unusually young.

"We can now confirm this. In our study we have been able to date three of these stars as relatively young, at least as far as astronomers are concerned, with ages of 100 million to about 1 billion years. This can be compared with the sun, which is 4.6 billion years old," says Rebecca Forsberg, researcher in astronomy at Lund University.

The nuclear star cluster has mainly been seen, quite rightly, as a very ancient part of the galaxy.

But the researchers' new discovery of such young stars indicates that there is also active star formation going on in this ancient component of the Milky Way.

However, dating stars 25,000 light years from Earth is not something that can be done in a hurry.

The researchers used high-resolution data from the Keck II telescope in Hawaii, one of the world's largest telescopes with a mirror ten metres in diameter.

For further verification, they then measured how much of the heavy element, iron, the stars contained.

The element is important for tracing the galaxy's development, as the theories the astronomers have about how stars are formed and galaxies develop indicate that young stars have more of the heavy elements, as heavy elements are formed to an increasing extent over time in the universe.

To determine the level of iron, the astronomers observed the stars' spectra in infrared light which, compared with optical light, are parts of the light spectrum that can more easily shine through the densely dust-laden parts of the Milky Way.

It was shown that the iron levels varied considerably, which surprised the researchers.

"The very wide spread of iron levels could indicate that the innermost parts of the galaxy are incredibly inhomogeneous, i.e. unmixed. This is something we had not expected and not only says something about how the centre of the galaxy appears, but also how the early universe may have looked," says Brian Thorsbro, researcher in astronomy at Lund University.

The study sheds significant light on our understanding of the early universe and the functioning of the very centre of the Milky Way.

The results may also be of benefit to inspire continued and future explorations of the heart of the galaxy, as well as the further development of models and simulations of the formation of galaxies and stars.

"Personally, I think it is very exciting that we can now study the very centre of our galaxy with such a high level of detail. These types of measurements have been standard for observations of the galactic disc where we are located, but have beenunreachable goal for more faraway and exotic parts of the galaxy. We can learn a lot about how our home galaxy was formed and developed from such studies," concludes Rebecca Forsberg.

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A gamma-ray pulsar milestone inspires innovative astrophysics and applications

The U.S. Naval Research Laboratory (NRL), in conjunction with the international Fermi Large Area Telescope Collaboration, announce the discovery of nearly 300 gamma ray pulsars in the publication of their Third Catalog of Gamma Ray Pulsars. This milestone comes 15 years since the launch of Fermi in 2008, when there were fewer than ten known gamma-ray pulsars.

"Work on this important catalog has been going on in our group for years," said Paul Ray, Ph.D., head of the High Energy Astrophysics and Applications Section at NRL.

"Our scientists and postdocs have been able to both discover and analyze the timing behavior and spectra of many of these newfound pulsars as part of our quest to further our understanding of these exotic stars that we are able to use as cosmic clocks."

Pulsars are formed when massive stars have burned though their fuel supply and become unable to resist the inward pull of their own gravity.

This results in the star collapsing into a dense, spinning magnetized neutron star.

Their spinning magnetic fields send out beams of gamma rays, the most energetic form of light.

As these beams sweep across the Earth, the highly sensitive Fermi gamma-ray telescope can observe their periodic pulses of energy.

With more than 15 years of data, Fermi has transformed the field of pulsar research.

"We have been very excited about how many millisecond pulsars (MSPs) we have been able to detect using these gamma rays," said Matthew Kerr, Ph.D., an NRL astrophysicist.

"We are able to study these objects that began as young pulsars in a binary system. Like a spinning top, they eventually slowed down and became inert. Over the past hundreds of millions of years, their binary companions dumped matter on to them, causing their speed to increase again, very dramatically and far faster than before, "recycling" these pulsars into MSPs. These high speed MSPs are now some of Nature's most precise timekeepers."

Scientists have been using these cosmic clocks in experiments called Pulsar Timing Arrays.

By searching for tiny deviations in the times at which the pulses arrive, scientist have been able to search for ripples in spacetime.

These ripples, known as gravitational waves, are produced when very massive objects, like pulsars, accelerate very quickly.

Very strong gravitational wave sources indicate a cataclysmic crash of dense, compact objects such as neutron stars and black holes.

Recently, several pulsar timing array collaborations, including several NRL researchers, published the first compelling evidence for very low-frequency gravitational waves, likely from the merger of supermassive black holes.

"These are such exciting results," said Thankful Cromartie, Ph.D., a National Research Council Research Associate at NRL.

"These low frequency gravitational waves allow us to peer into the centers of massive galaxies and better understand how they were formed."

The pulsar timing array results have important practical applications as well.

The spacetime distortions set a limit on how precisely we can use pulsars for critical navigation and timing.

In pulsar-based navigation, these spinning pulsars play much the same role as GPS satellites do, but we are able to use them far beyond the Earth's orbit.

"Now we know where that ultimate stability limit is," said Dr. Ray.

Using Fermi's gamma ray detection abilities are also having an impact on pulsar timing array work.

"Previously, once we found an MSP we had to hand it off to radio astronomers to monitor with huge telescopes," said Dr. Kerr.

"What we have found is that Fermi is sensitive enough by itself to constrain these gravitational waves and, unlike radio waves, which are bent like the light in a prism as they travel to earth, the gamma rays shoot straight to us. This reduces potential systemic errors in measurements."

For Megan DeCesar, Ph.D., a George Mason University scientist working at NRL, the most intriguing aspect of the new work in the dramatic increase of "spider" pulsars.

"Spider pulsars are named after arachnids that eat their smaller mates," DeCesar said.

"Something similar can happen when a neutron star and its binary companion are very close to each other and the MSP "recycling" process gets a little carried away. The intense radiation and particle wind from the pulsar eats away at the surface of the other star, resulting in a puffball of evaporated material."

When compared to radio observations, Fermi is particularly adept at finding these "spiders" as, in many cases, radio waves are eclipsed as the pulsar beam passes the remnants of the companion star.

Gamma rays, however, are capable of passing right through. "While it may be that spider systems are also intrinsically brighter in gamma rays, studying them will help us to understand their origins and the bonanza of discoveries we have made with Fermi," said DeCesar.

Read more at Science Daily

Telescope Array detects second highest-energy cosmic ray ever

In 1991, the University of Utah Fly's Eye experiment detected the highest-energy cosmic ray ever observed. Later dubbed the Oh-My-God particle, the cosmic ray's energy shocked astrophysicists. Nothing in our galaxy had the power to produce it, and the particle had more energy than was theoretically possible for cosmic rays traveling to Earth from other galaxies. Simply put, the particle should not exist.

The Telescope Array has since observed more than 30 ultra-high-energy cosmic rays, though none approaching the Oh-My-God-level energy. No observations have yet revealed their origin or how they are able to travel to the Earth.

On May 27, 2021, the Telescope Array experiment detected the second-highest extreme-energy cosmic ray. At 2.4 x 1020eV, the energy of this single subatomic particle is equivalent to dropping a brick on your toe from waist height. Led by the University of Utah (the U) and the University of Tokyo, the Telescope Array consists of 507 surface detector stations arranged in a square grid that covers 700 km2 (~270 miles2) outside of Delta, Utah in the state's West Desert. The event triggered 23 detectors at the north-west region of the Telescope Array, splashing across 48 km2 (18.5 mi2). Its arrival direction appeared to be from the Local Void, an empty area of space bordering the Milky Way galaxy.

"The particles are so high energy, they shouldn't be affected by galactic and extra-galactic magnetic fields. You should be able to point to where they come from in the sky," said John Matthews, Telescope Array co-spokesperson at the U and co-author of the study. "But in the case of the Oh-My-God particle and this new particle, you trace its trajectory to its source and there's nothing high energy enough to have produced it. That's the mystery of this -- what the heck is going on?"

In their observation that published on Nov. 24, 2023, in the journal Science, an international collaboration of researchers describe the ultra-high-energy cosmic ray, evaluate its characteristics, and conclude that the rare phenomena might follow particle physics unknown to science. The researchers named it the Amaterasu particle after the sun goddess in Japanese mythology. The Oh-My-God and the Amaterasu particles were detected using different observation techniques, confirming that while rare, these ultra-high energy events are real.

"These events seem like they're coming from completely different places in the sky. It's not like there's one mysterious source," said John Belz, professor at the U and co-author of the study. "It could be defects in the structure of spacetime, colliding cosmic strings. I mean, I'm just spit-balling crazy ideas that people are coming up with because there's not a conventional explanation."

Natural particle accelerators

Cosmic rays are echoes of violent celestial events that have stripped matter to its subatomic structures and hurled it through universe at nearly the speed of light. Essentially cosmic rays are charged particles with a wide range of energies consisting of positive protons, negative electrons, or entire atomic nuclei that travel through space and rain down onto Earth nearly constantly.

Cosmic rays hit Earth's upper atmosphere and blasts apart the nucleus of oxygen and nitrogen gas, generating many secondary particles. These travel a short distance in the atmosphere and repeat the process, building a shower of billions of secondary particles that scatter to the surface. The footprint of this secondary shower is massive and requires that detectors cover an area as large as the Telescope Array. The surface detectors utilize a suite of instrumentation that gives researchers information about each cosmic ray; the timing of the signal shows its trajectory and the amount of charged particles hitting each detector reveals the primary particle's energy.

Because particles have a charge, their flight path resembles a ball in a pinball machine as they zigzag against the electromagnetic fields through the cosmic microwave background. It's nearly impossible to trace the trajectory of most cosmic rays, which lie on the low- to middle-end of the energy spectrum. Even high-energy cosmic rays are distorted by the microwave background. Particles with Oh-My-God and Amaterasuenergy blast through intergalactic space relatively unbent. Only the most powerful of celestial events can produce them.

"Things that people think of as energetic, like supernova, are nowhere near energetic enough for this. You need huge amounts of energy, really high magnetic fields to confine the particle while it gets accelerated," said Matthews.

Ultra-high-energy cosmic rays must exceed 5 x 1019 eV. This means that a single subatomic particle carries the same kinetic energy as a major league pitcher's fast ball and has tens of millions of times more energy than any human-made particle accelerator can achieve. Astrophysicists calculated this theoretical limit, known as the Greisen-Zatsepin-Kuzmin (GZK) cutoff, as the maximum energy a proton can hold traveling over long distances before the effect of interactions of the microwave background radiation take their energy. Known source candidates, such as active galactic nuclei or black holes with accretion disks emitting particle jets, tend to be more than 160 million light years away from Earth. The new particle's 2.4 x 1020 eV and the Oh-My-God particle's 3.2 x 1020 eV easily surpass the cutoff.

Researchers also analyze cosmic ray composition for clues of its origins. A heavier particle, like iron nuclei, are heavier, have more charge and are more susceptible to bending in a magnetic field than a lighter particle made of protons from a hydrogen atom. The new particle is likely a proton. Particle physics dictates that a cosmic ray with energy beyond the GZK cutoff is too powerful for the microwave background to distort its path, but back tracing its trajectory points towards empty space.

"Maybe magnetic fields are stronger than we thought, but that disagrees with other observations that show they're not strong enough to produce significant curvature at these ten-to-the-twentieth electron volt energies," said Belz. "It's a real mystery."

Expanding the footprint

The Telescope Array is uniquely positioned to detect ultra-high-energy cosmic rays. It sits at about 1,200 m (4,000 ft), the elevation sweet-spot that allows secondary particles maximum development, but before they start to decay. Its location in Utah's West Desert provides ideal atmospheric conditions in two ways: the dry air is crucial because humidity will absorb the ultraviolet light necessary for detection; and the region's dark skies are essential, as light pollution will create too much noise and obscure the cosmic rays.

Read more at Science Daily

Astrophysicists scan the Galaxy for signs of life

Astrophysicists from Trinity College Dublin are scanning the Universe for "technosignatures" emanating from distant planets that would provide support for the existence of intelligent, alien life.

Using the Irish LOFAR telescope and its counterpart in Onsala, Sweden, the team -- led by Professor Evan Keane, Associate Professor of Radio Astronomy in Trinity's School of Physics, and Head of the Irish LOFAR Telescope -- plans to monitor millions of star systems.

Scientists have been searching for extraterrestrial radio signals for well over 60 years. Many of these have been carried out using single observatories which limits the ability to identify signals from the haze of terrestrial interference on Earth. Much of the effort has focused on frequencies above 1 GHz because the single-dish telescopes employed operate at these frequencies.

Now, a new collaboration led by Trinity College Dublin, with the Breakthrough Listen team and Onsala Space Observatory in Sweden, is perfecting a multi-site, multi-telescope technique that allows them to search at much lower frequencies of 110 -- 190 MHz.

The Breakthrough Listen programme is the most comprehensive search for technologically advanced extraterrestrial life, developing dedicated instruments at the Irish and Swedish LOFAR stations. Using multiple sites has the major benefit that it is much less likely to provide a "false positive" signal; such signals arise due to interference from many human sources on Earth.

The team has just published details of their method and their ongoing search in the Astronomical Journal They have already scanned 1.6 million star systems flagged as interesting targets by the Gaia and TESS space missions, run by ESA and NASA respectively. So far these searches have drawn a blank.

But the search has only just begun...

Prof. Keane said: "In the last 50 years evidence has steadily mounted that the constituents and conditions necessary for life are relatively common in the Universe, which begs one of life's greatest unanswered questions: are we really alone?

"To some people the 'Search for Extra-terrestrial Intelligence, or SETI' might seem like something from a movie, but it has been a scientific pursuit for decades, and for a host of very good reasons. With this project we are basing our search on the common assumption that civilisations elsewhere in the Universe may employ similar technologies to those developed on Earth. As a result radio frequencies are a logical domain for conducting SETI surveys due to the widespread use of telecommunications and radar and our access to next-gen radio telescopes offers a great chance for a deep dive into the Universe."

Owen Johnson, PhD Candidate in Trinity's School of Physics, is the first author of the journal article, and the first Irish person to ever undertake a PhD on the topic of SETI. He added:

"What makes surveys like this one truly captivating is the fact that we're pushing these telescopes to their absolute limits, directing them towards substantial portions of the sky. As a result, we have the exciting possibility of discovering all sorts of wild and wondrous phenomena during this process and if we're very fortunate, even encountering our cosmic neighbours.

"LOFAR is soon to undergo a staged series of upgrades across all stations in the array across Europe, which will allow an even broader SETI at ranges of 15 -- 240 MHz. We have billions of star systems to explore and will be relying on some machine learning techniques to sift through the immense volume of data.

Read more at Science Daily

Pulsars may make dark matter glow

The central question in the ongoing hunt for dark matter is: what is it made of? One possible answer is that dark matter consists of particles known as axions. A team of astrophysicists, led by researchers from the universities of Amsterdam and Princeton, has now shown that if dark matter consists of axions, it may reveal itself in the form of a subtle additional glow coming from pulsating stars.

Dark matter may be the most sought-for constituent of our universe. Surprisingly, this mysterious form of matter, that physicist and astronomers so far have not been able to detect, is assumed to make up an enormous part of what is out there. No less than 85% of matter in the universe is suspected to be 'dark', presently only noticeable through the gravitational pull it exerts on other astronomical objects. Understandably, scientists want more. They want to really see dark matter -- or at the very least, detect its presence directly, not just infer it from gravitational effects. And, of course: they want to know what it is.

Cleaning up two problems

One thing is clear: dark matter cannot be the same type of matter that you and I are made of. If that were to be the case, dark matter would simply behave like ordinary matter -- it would form objects like stars, light up, and no longer be 'dark'. Scientists are therefore looking for something new -- a type of particle that nobody has detected yet, and that probably only interacts very weakly with the types of particles that we know, explaining why this constituent of our world so far has remained elusive.

There are plenty of clues for where to look. One popular assumption is that dark matter could be made of axions. This hypothetical type of particle was first introduced in the 1970s to resolve a problem that had nothing to do with dark matter. The separation of positive and negative charges inside the neutron, one of the building blocks of ordinary atoms, turned out to be unexpectedly small. Scientists of course wanted to know why. It turned out that the presence of a hitherto undetected type of particle, interacting very weakly with the neutron's constituents, could cause exactly such an effect. The later Nobel Prize winner Frank Wilczek came up with a name for the new particle: axion -- not just similar to other particle names like proton, neutron, electron and photon, but also inspired by a laundry detergent of the same name. The axion was there to clean up a problem.

In fact, despite never being detected, it might clean up two. Several theories for elementary particles, including string theory, one of the leading candidate theories to unify all forces in nature, appeared to predict that axion-like particles could exist. If axions were indeed out there, could they also constitute part or even all of the missing dark matter? Perhaps, but an additional question that haunted all dark matter research was just as valid for axions: if so, then how can we see them? How does one make something 'dark' visible?

Shining a light on dark matter

Fortunately, it seems that for axions there may be a way out of this conundrum. If the theories that predict axions are correct, they are not only expected to be mass-produced in the universe, but some axions could also be converted into light in the presence of strong electromagnetic fields. Once there is light, we can see. Could this be the key to detect axions -- and therefore to detect dark matter?

To answer that question, scientists first had to ask themselves where in the universe the strongest known electric and magnetic fields occur. The answer is: in regions surrounding rotating neutron stars also known as pulsars. These pulsars -- short for 'pulsating stars' -- are dense objects, with a mass roughly the same as that of our Sun, but a radius that is around 100,000 times smaller, only about 10 km. Being so small, pulsars spin with enormous frequencies, emitting bright narrow beams of radio emission along their axis of rotation. Similar to a lighthouse, the pulsar's beams can sweep across the Earth, making the pulsating star easily observable.

However, the pulsar's enormous spin does more. It turns the neutron star into an extremely strong electromagnet. That, in turn, could mean that pulsars are very efficient axion factories. Every single second an average pulsar would be capable of producing a 50-digit number of axions. Because of the strong electromagnetic field around the pulsar, a fraction of these axions could convert into observable light. That is: if axions exist at all -- but the mechanism can now be used to answer just that question. Just look at pulsars, see if they emit extra light, and if they do, determine whether this extra light could be coming from axions.

Simulating a subtle glow

As always in science, actually performing such an observation is of course not that simple. The light emitted by axions -- detectable in the form of radio waves -- would only be a small fraction of the total light that these bright cosmic lighthouses send our way. One needs to know very precisely what a pulsar without axions would look like, and what a pulsar with axions would look like, to be able to see the difference -- let alone to quantify that difference and turn it into a measurement of an amount of dark matter.

This is exactly what a team of physicists and astronomers have now done. In a collaborative effort between the Netherlands, Portugal and the USA, the team has constructed a comprehensive theoretical framework which allows for the detailed understanding of how axions are produced, how axions escape the gravitational pull of the neutron star, and how, during their escape, they convert into low energy radio radiation.

The theoretical results were then put on a computer to model the production of axions around pulsars, using state-of-the-art numerical plasma simulations that were originally developed to understand the physics behind how pulsars emit radio waves. Once virtually produced, the propagation of the axions through the electromagnetic fields of the neutron star was simulated. This allowed the researchers to quantitatively understand the subsequent production of radio waves and model how this process would provide an additional radio signal on top of the intrinsic emission generated from the pulsar itself.

Putting axion models to a test

The results from theory and simulation were then put to a first observational test. Using observations from 27 nearby pulsars, the researchers compared the observed radio waves to the models, to see if any measured excess could provide evidence for the existence of axions. Unfortunately, the answer was 'no' -- or perhaps more optimistically: 'not yet'. Axions do not immediately jump out to us, but perhaps that was not to be expected. If dark matter were to give up its secrets that easily, it would already have been observed a long time ago.

The hope for a smoking-gun detection of axions, therefore, is now on future observations. Meanwhile, the current non-observation of radio signals from axions is an interesting result in itself. The first comparison between simulations and actual pulsars has placed the strongest limits to date on the interaction that axions can have with light.

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Unprecedented gamma-ray burst explained by long-lived jet

Last year, Northwestern University researchers reported new observational evidence that long gamma-ray bursts (GRBs) can result from the merger of a neutron star with another compact object (either another neutron star or black hole) -- a finding that was previously believed to be impossible.

Now, another Northwestern team offers a potential explanation for what generated the unprecedented and incredibly luminous burst of light.

After developing the first numerical simulation that follows the jet evolution in a black hole-neutron star merger out to large distances, the astrophysicists discovered that the post-merger black hole can launch jets of material from the swallowed neutron star.

But the key ingredients are the mass of the violent whirlpool of gas (or accretion disk) surrounding the black hole and the strength of the disk's magnetic field. In massive disks, when the magnetic field is strong, the black hole launches a short-duration jet that is much brighter than anything ever seen in observations. When the massive disk has a weaker magnetic field, however, the black hole launches a jet with the same luminosity and long duration as the mysterious GRB (dubbed GRB211211A) spotted in 2021 and reported in 2022.

Not only does the new discovery help explain the origins of long GRBs, it also gives insight into the nature and physics of black holes, their magnetic fields and accretion disks.

The study will be published Thursday (Aug. 31) in the Astrophysical Journal.

"So far, no one else has developed any numerical works or simulations that consistently follow a jet from the compact-object merger to the formation of the jet and its large-scale evolution," said Northwestern's Ore Gottlieb, who co-led the work. "The motivation for our work was to do this for the first time. And what we found just so happened to match observations of GRB211211A."

"Neutron-star mergers are a captivating multi-messenger phenomena, which result in both gravitational and electromagnetic waves," said Northwestern's Danat Issa, who co-led the work with Gottlieb. "However, simulating these events poses a challenge due to the vast spatial and temporal scale separations involved as well as the diverse physics operating across these scales. For the first time, we have succeeded in comprehensively modeling the entire sequence of the neutron star merger process."

During the research, Gottlieb was a CIERA Fellow at Northwestern's Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA); now he is a Flatiron Research Fellow at the Flatiron Institute's Center for Computational Astrophysics. Issa is a graduate student in the Department of Physics and Astronomy at Northwestern's Weinberg College of Arts and Sciences and member of CIERA. Issa is advised by paper co-author Alexander Tchekhovskoy, an associate professor of physics and astronomy at Weinberg and member of CIERA.

Curious kilonova

When astronomers first spotted GRB211211A in December 2021, they initially assumed that the 50-second-long event was generated from the collapse of a massive star. But, as they examined the long GRB's late-time emission, called the afterglow, they uncovered evidence of a kilonova, a rare event that only occurs after the merger of a neutron star with another compact object.

The finding (published in Nature in December 2022) upended the long-established, long-accepted belief that only supernovae could generate long GRBs.

"GRB 211211A reignited interest in the origin of long-duration GRBs that are not associated with massive stars, but likely originating from compact binary mergers," Gottlieb said.

From pre-merger to long GRB

To further reveal what occurs during compact-merger events, Gottlieb, Issa and their collaborators sought to simulate the whole process -- from before the merger all the way through to the end of the GRB event, when the GRB-producing jets shut off. Because it is such an incredibly computationally expensive feat, the entire scenario had never been modeled before. Gottlieb and Issa overcame that challenge by dividing the scenario into two simulations.

First, the researchers ran a simulation of the pre-merger phase. Then, they took the output from the first simulation and plugged it into the post-merger simulation.

"Because the space-time used by the two simulations is different, this remap was not as straightforward as we had hoped, but Danat figured it out," Tchekhovskoy said.

"The daisy chaining of the two simulations allowed us to make the computation much less expensive," Gottlieb said. "The physics is very complicated in the pre-merger stage because there are two objects. It gets much simpler after the pre-merger because there is only one black hole."

In the simulation, the compact objects first merged to create a more massive black hole. The black hole's intense gravity pulled the now-destroyed neutron star's debris toward it. Before the debris fell into the black hole, some of the debris first swirled around the black hole as an accretion disk. In the configuration studied, the emerging disk was particularly massive with one-tenth the mass of our sun. Then, when the mass fell into the black hole from the disk, it powered the black hole to launch a jet that accelerated to near light speed.

Disk properties matter

A surprise emerged as the researchers adjusted the strength of the massive disk's magnetic field. Whereas a strong magnetic field resulted in a short, incredibly bright GRB, a weak magnetic field generated a jet that matched observations of long GRBs.

"The stronger the magnetic field, the shorter is its lifetime," Gottlieb said. "Weak magnetic fields produce weaker jets that the newly formed black hole can sustain for a longer time. A key ingredient here is the massive disk that can maintain, together with weak magnetic fields, a GRB consistent with observations and comparable to the luminosity and long duration of GRB211211A. Although we found this specific binary system to give rise to a long GRB, we also expect that other binary mergers that produce massive disks will lead to a similar outcome. It's simply a question of the post-merger disk mass."

Of course, "long" is relative in this scenario. GRBs are divided into two classes. GRBs with durations less than two seconds are considered short. If a GRB is two seconds or longer, then it's considered long. Even events this brief are still exceptionally difficult to model.

"A major portion of this disk material ultimately gets consumed by the black hole, with the whole process lasting mere seconds," Issa said. "Here lies the main challenge: It is very difficult to capture the evolution of these mergers, using simulations on supercomputers, over a span of several seconds."

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Why the day is 24 hours long: Astrophysicists reveal why Earth's day was a constant 19.5 hours for over a billion years

A team of astrophysicists at the University of Toronto (U of T) has revealed how the slow and steady lengthening of Earth's day caused by the tidal pull of the moon was halted for over a billion years.

They show that from approximately two billion years ago until 600 million years ago, an atmospheric tide driven by the sun countered the effect of the moon, keeping Earth's rotational rate steady and the length of day at a constant 19.5 hours.

Without this billion-year pause in the slowing of our planet's rotation, our current 24-hour day would stretch to over 60 hours.

The study describing the result, 'Why the day is 24 hours long; the history of Earth's atmospheric thermal tide, composition, and mean temperature,' was published today in the journal Science Advances. Drawing on geological evidence and using atmospheric research tools, the scientists show that the tidal stalemate between the sun and moon resulted from the incidental but enormously consequential link between the atmosphere's temperature and Earth's rotational rate.

The paper's authors include Norman Murray, a theoretical astrophysicist with U of T's Canadian Institute for Theoretical Astrophysics (CITA); graduate student Hanbo Wu, CITA and Department of Physics, U of T; Kristen Menou, David A. Dunlap Department of Astronomy & Astrophysics and Department of Physical & Environmental Sciences, University of Toronto Scarborough; Jeremy Laconte, Laboratoire d'astrophysique de Bordeaux and and a former CITA postdoctoral fellow; and Christopher Lee, Department of Physics, U of T.

When the moon first formed some 4.5 billion years ago, the day was less than 10 hours long. But since then, the moon's gravitational pull on the Earth has been slowing our planet's rotation, resulting in an increasingly longer day. Today, it continues to lengthen at a rate of some 1.7 milliseconds every century.

The moon slows the planet's rotation by pulling on Earth's oceans, creating tidal bulges on opposite sides of the planet that we experience as high and low tides. The gravitational pull of the moon on those bulges, plus the friction between the tides and the ocean floor, acts like a brake on our spinning planet.

"Sunlight also produces an atmospheric tide with the same type of bulges," says Murray. "The sun's gravity pulls on these atmospheric bulges, producing a torque on the Earth. But instead of slowing down Earth's rotation like the moon, it speeds it up."

For most of Earth's geological history, the lunar tides have overpowered the solar tides by about a factor of ten; hence, the Earth's slowing rotational speed and lengthening days.

But some two billion years ago, the atmospheric bulges were larger because the atmosphere was warmer and because its natural resonance -- the frequency at which waves move through it -- matched the length of day.

The atmosphere, like a bell, resonates at a frequency determined by various factors, including temperature. In other words, waves -- like those generated by the enormous eruption of the volcano Krakatoa in Indonesia in 1883 -- travel through it at a velocity determined by its temperature. The same principle explains why a bell always produces the same note if its temperature is constant.

Throughout most of Earth's history that atmospheric resonance has been out of sync with the planet's rotational rate. Today, each of the two atmospheric "high tides" take 22.8 hours to travel around the world; because that resonance and Earth's 24-hour rotational period are out of sync, the atmospheric tide is relatively small.

But during the billion-year period under study, the atmosphere was warmer and resonated with a period of about 10 hours. Also, at the advent of that epoch, Earth's rotation, slowed by the moon, reached 20 hours.

When the atmospheric resonance and length of day became even factors -- ten and 20 -- the atmospheric tide was reinforced, the bulges became larger and the sun's tidal pull became strong enough to counter the lunar tide.

"It's like pushing a child on a swing," says Murray. "If your push and the period of the swing are out of sync, it's not going to go very high. But, if they're in sync and you're pushing just as the swing stops at one end of its travel, the push will add to the momentum of the swing and it will go further and higher. That's what happened with the atmospheric resonance and tide."

Along with geological evidence, Murray and his colleagues achieved their result using global atmospheric circulation models (GCMs) to predict the atmosphere's temperature during this period. The GCMs are the same models used by climatologists to study global warming. According to Murray, the fact they worked so well in the team's research is a timely lesson.

"I've talked to people who are climate change skeptics who don't believe in the global circulation models that are telling us we're in a climate crisis," says Murray. "And I tell them: We used these global circulation models in our research, and they got it right. They work."

Despite its remoteness in geological history, the result adds additional perspective to the climate crisis. Because the atmospheric resonance changes with temperature, Murray points out that our current warming atmosphere could have consequences in this tidal imbalance.

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Astrophysicists propose a new way of measuring cosmic expansion: Lensed gravitational waves

The universe is expanding; we've had evidence of that for about a century. But just how quickly celestial objects are receding from each other is still up for debate.

It's no small feat to measure the rate at which objects move away from each other across vast distances. Since the discovery of cosmic expansion, its rate has been measured and re-measured with increasing precision, with some of the latest values ranging from 67.4 up to 76.5 kilometers per second per megaparsec, which relates the recession velocity (in kilometers per second) to the distance (in megaparsecs).

The discrepancy between different measurements of cosmic expansion is called the "Hubble tension." Some have called it a crisis in cosmology. But for UC Santa Barbara theoretical astrophysicist Tejaswi Venumadhav Nerella and colleagues at the Tata Institute of Fundamental Research in Bangalore, India, and the Inter-University Center for Astronomy and Astrophysics in Pune, India, it is an exciting time.

Since the first detection of gravitational waves in 2015, detectors have been significantly improved and are poised to yield a rich haul of signals in the coming years. Nerella and his colleagues have come up with a method to use these signals to measure the universe's expansion, and perhaps help to settle the debate once and for all. "A major scientific goal of future detectors is to deliver a comprehensive catalog of gravitational wave events, and this will be a completely novel use of the remarkable dataset," said Nerella, co-author of a paper published in Physical Review Letters.

Measurements of the cosmic expansion rate boil down to velocity and distance. Astronomers use two kinds of methods to measure distances: the first start with objects with a known length ("standard rulers") and look at how big they appear in the sky. These "objects" are features in cosmic background radiation, or in the distribution of galaxies in the universe.

A second class of methods starts with objects of known luminosity ("standard candles") and measures their distances from Earth using their apparent brightness. These distances are connected to those of farther bright objects and so on, which builds up a chain of measurement schemes that is often called the "cosmic distance ladder." Incidentally, gravitational waves themselves can also help measure cosmic expansion, since the energy released by the collision of neutron stars or black holes can be used to estimate the distance to these objects.

The method that Nerella and his co-authors propose belongs to the second class but uses gravitational lensing. This is a phenomenon that occurs when massive objects warp spacetime, and bend waves of all kinds that travel near the objects. In rare cases, lensing can produce multiple copies of the same gravitational wave signal that reach Earth at different times -- the delays between the signals for a population of multiple imaged events can be used to calculate the universe's expansion rate, according to the researchers.

"We understand very well just how sensitive gravitational wave detectors are, and there are no astrophysical sources of confusion, so we can properly account for what gets into our catalog of events," Nerella said. "The new method has sources of error that are complementary to those of existing methods, which makes it a good discriminator."

The sources of these signals would be binary black holes: systems of two black holes that orbit each other and ultimately merge, releasing massive amounts of energy in the form of gravitational waves. We haven't yet detected strongly lensed examples of these signals, but the upcoming generation of ground-based detectors is expected to have the necessary level of sensitivity.

"We expect the first observation of lensed gravitational waves in the next few years," said study co-author Parameswaran Ajith. Additionally, these future detectors should be able to see farther into space and detect weaker signals.

The authors expect these advanced detectors to start their search for merging black holes in the next decade. They anticipate recording signals from a few million black hole pairs, a small fraction (about 10,000) of which will appear multiple times in the same detector due to gravitational lensing. The distribution of the delays between these repeat appearances encodes the Hubble expansion rate.

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