Dwarf galaxies use 10-million-year quiet period to churn out stars

If you look at massive galaxies teeming with stars, you might be forgiven in thinking they are star factories, churning out brilliant balls of gas. But actually, less evolved dwarf galaxies have bigger regions of star factories, with higher rates of star formation.

Now, University of Michigan researchers have discovered the reason underlying this: These galaxies enjoy a 10-million-year delay in blowing out the gas cluttering up their environments.

Star-forming regions are able to hang on to their gas and dust, allowing more stars to coalesce and evolve.

In these relatively pristine dwarf galaxies, massive stars -- stars about 20 to 200 times the mass of our sun -- collapse into black holes instead of exploding as supernovae.

But in more evolved, polluted galaxies, like our Milky Way, they are more likely to explode, thereby generating a collective superwind.

Gas and dust get blasted out of the galaxy, and star formation quickly stops.

Their findings are published in the Astrophysical Journal.

"As stars go supernova, they pollute their environment by producing and releasing metals," said Michelle Jecmen, study first author and an undergraduate researcher.

"We argue that at low metallicity -- galaxy environments that are relatively unpolluted -- there is a 10-million-year delay in the start of strong superwinds, which, in turn, results in higher star formation."

The U-M researchers point to what's called the Hubble tuning fork, a diagram that depicts the way astronomer Edwin Hubble classified galaxies.

In the handle of the tuning fork are the largest galaxies. Huge, round and brimming with stars, these galaxies have already turned all of their gas into stars.

Along the tines of the tuning fork are spiral galaxies that do have gas and star-forming regions along their compact arms.

At the end of the tuning fork's tines are the least evolved, smallest galaxies.

"But these dwarf galaxies have just these really mondo star-forming regions," said U-M astronomer Sally Oey, senior author of the study.

"There have been some ideas around why that is, but Michelle's finding offers a very nice explanation: These galaxies have trouble stopping their star formation because they don't blow away their gas."

Additionally, this 10-million-year period of quiet offers astronomers the opportunity to peer at scenarios similar to the cosmic dawn, a period of time just after the Big Bang, Jecmen said.

In pristine dwarf galaxies, gas clumps together and forms gaps through which radiation can escape.

This previously known phenomenon is called the "picket fence" model, with UV radiation escaping between slats in the fence.

The delay explains why gas would have had time to clump together.

Ultraviolet radiation is important because it ionizes hydrogen -- a process that also occurred right after the Big Bang, causing the universe to go from opaque to transparent.

"And so looking at low-metallicity dwarf galaxies with lots of UV radiation is somewhat similar to looking all the way back to the cosmic dawn," Jecmen said.

"Understanding the time near the Big Bang is so interesting. It's foundational to our knowledge. It's something that happened so long ago -- it's so fascinating that we can see sort of similar situations in galaxies that exist today."

A second study, published in the Astrophysical Journal Letters and led by Oey, used the Hubble Space Telescope to look at Mrk 71, a region in a nearby dwarf galaxy about 10 million light years away.

In Mrk 71, the team found observational evidence of Jecmen's scenario.

Using a new technique with the Hubble Space Telescope, the team employed a filter set that looks at the light of triply ionized carbon.

In more evolved galaxies with lots of supernova explosions, those explosions heat gas in a star cluster to very high temperatures -- to millions of degrees Kelvin, Oey said.

As this hot superwind expands, it blasts the rest of the gas out of the star clusters.

But in low metallicity environments such as Mrk 71, where stars aren't blowing up, energy within the region is radiated away.

It doesn't have the chance to form a superwind.

The team's filters picked up a diffuse glow of the ionized carbon throughout Mrk 71, demonstrating that the energy is radiating away.

Therefore, there is no hot superwind, instead allowing dense gas to remain throughout the environment.

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NASA's Webb captures an ethereal view of NGC 346

Filaments of dust and gas festoon this star-forming region in a new infrared image from MIRI.

One of the greatest strengths of NASA's James Webb Space Telescope is its ability to give astronomers detailed views of areas where new stars are being born. The latest example, showcased here in a new image from Webb's Mid-Infrared Instrument (MIRI), is NGC 346 -- the brightest and largest star-forming region in the Small Magellanic Cloud.

The Small Magellanic Cloud (SMC) is a satellite galaxy of the Milky Way, visible to the unaided eye in the southern constellation Tucana. This small companion galaxy is more primeval than the Milky Way in that it possesses fewer heavy elements, which are forged in stars through nuclear fusion and supernova explosions, compared to our own galaxy.

Since cosmic dust is formed from heavy elements like silicon and oxygen, scientists expected the SMC to lack significant amounts of dust. However the new MIRI image, as well as a previous image of NGC 346 from Webb's Near-Infrared Camera released in January, show ample dust within this region.

In this representative-color image, blue tendrils trace emission from material that includes dusty silicates and sooty chemical molecules known as polycyclic aromatic hydrocarbons, or PAHs. More diffuse red emission shines from warm dust heated by the brightest and most massive stars in the heart of the region. An arc at the center left may be a reflection of light from the star near the arc's center. (Similar, fainter arcs appear associated with stars at lower left and upper right.) Lastly, bright patches and filaments mark areas with abundant numbers of protostars. The research team looked for the reddest stars, and found 1,001 pinpoint sources of light, most of them young stars still embedded in their dusty cocoons.

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Stellar cradles and graves seen in farthest galaxy ever

New observations using the Atacama Large Millimeter/submillimeter Array (ALMA) have distinguished the sites of star formation and a possible site of star death from the surrounding nebula in a galaxy 13.2 billion light-years away. This is the farthest that such structures have been observed.

A team led by Yoichi Tamura, an astronomer at Nagoya University, attempted high-resolution observations of MACS0416_Y1, located 13.2 billion light-years away in the constellation Eridanus. Previous observations of this galaxy by the same team had detected radio waves emitted by both oxygen and dust, two components of interstellar nebulae. Detailed observations of the distribution of dust and oxygen can provide clues about how stars are born and die within nebulae, but the observations had lacked the resolution needed to see the structure of the nebulae.

This time the team observed with ALMA for 28 hours, zooming in on MACS0416_Y1. The results showed that the dust signal regions and oxygen emission regions are intricately intertwined, avoiding each other, suggesting the process where newly formed stars within the nebulae ionize the surrounding gas.

Furthermore, the team found a massive cavity spanning approximately 1,000 light-years in the dust dominated regions. When many new, massive and short-lived stars are born together, the resulting successive supernova explosions create enormous "superbubbles" in the nebulae. The discovered cavity may indeed be such a superbubble.

Takuya Hashimoto from the University of Tsukuba describes the observation performance as follows: "It corresponds to capturing the extremely weak light emitted by two fireflies located 3 centimeters apart on the summit of Mount Fuji as seen from Tokyo, and being able to distinguish between those two fireflies."

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Webb celebrates first year of science with close-up on birth of sun-like stars

From our cosmic backyard in the solar system to distant galaxies near the dawn of time, NASA's James Webb Space Telescope has delivered on its promise of revealing the universe like never before in its first year of science operations. To celebrate the completion of a successful first year, NASA has released Webb's image of a small star-forming region in the Rho Ophiuchi cloud complex.

"In just one year, the James Webb Space Telescope has transformed humanity's view of the cosmos, peering into dust clouds and seeing light from faraway corners of the universe for the very first time. Every new image is a new discovery, empowering scientists around the globe to ask and answer questions they once could never dream of," said NASA Administrator Bill Nelson. "Webb is an investment in American innovation but also a scientific feat made possible with NASA's international partners that share a can-do spirit to push the boundaries of what is known to be possible. Thousands of engineers, scientists, and leaders poured their life's passion into this mission, and their efforts will continue to improve our understanding of the origins of the universe -- and our place in it."

The new Webb image released today features the nearest star-forming region to us. Its proximity at 390 light-years allows for a highly detailed close-up, with no foreground stars in the intervening space.

"On its first anniversary, the James Webb Space Telescope has already delivered upon its promise to unfold the universe, gifting humanity with a breathtaking treasure trove of images and science that will last for decades," said Nicola Fox, associate administrator of NASA's Science Mission Directorate in Washington. "An engineering marvel built by the world's leading scientists and engineers, Webb has given us a more intricate understanding of galaxies, stars, and the atmospheres of planets outside of our solar system than ever before, laying the groundwork for NASA to lead the world in a new era of scientific discovery and the search for habitable worlds."

Webb's image shows a region containing approximately 50 young stars, all of them similar in mass to the Sun, or smaller. The darkest areas are the densest, where thick dust cocoons still-forming protostars. Huge bipolar jets of molecular hydrogen, represented in red, dominate the image, appearing horizontally across the upper third and vertically on the right. These occur when a star first bursts through its natal envelope of cosmic dust, shooting out a pair of opposing jets into space like a newborn first stretching her arms out into the world. In contrast, the star S1 has carved out a glowing cave of dust in the lower half of the image. It is the only star in the image that is significantly more massive than the Sun.

"Webb's image of Rho Ophiuchi allows us to witness a very brief period in the stellar lifecycle with new clarity. Our own Sun experienced a phase like this, long ago, and now we have the technology to see the beginning of another's star's story," said Klaus Pontoppidan, who served as Webb project scientist at the Space Telescope Science Institute in Baltimore, Maryland, since before the telescope's launch and through the first year of operations.

Some stars in the image display tell-tale shadows indicating protoplanetary disks -- potential future planetary systems in the making.

A Full Year, Across the Full Sky

From its very first deep field image, unveiled by President Joe Biden, Vice President Kamala Harris, and Nelson live at the White House, Webb has delivered on its promise to show us more of the universe than ever before. However, Webb revealed much more than distant galaxies in the early universe.

"The breadth of science Webb is capable of exploring really becomes clear now, when we have a full year's worth of data from targets across the sky," said Eric Smith, associate director for research in the Astrophysics Division at NASA Headquarters and Webb program scientist. "Webb's first year of science has not only taught us new things about our universe, but it has revealed the capabilities of the telescope to be greater than our expectations, meaning future discoveries will be even more amazing." The global astronomy community has spent the past year excitedly poring over Webb's initial public data and getting a feel for how to work with it.

Beyond the stunning infrared images, what really has scientists excited are Webb's crisp spectra -- the detailed information that can be gleaned from light by the telescope's spectroscopic instruments. Webb's spectra have confirmed the distances of some of the farthest galaxies ever observed, and have discovered the earliest, most distant supermassive black holes. They have identified the compositions of planet atmospheres (or lack thereof) with more detail than ever before, and have narrowed down what kinds of atmospheres may exist on rocky exoplanets for the first time. They also have revealed the chemical makeup of stellar nurseries and protoplanetary disks, detecting water, organic carbon-containing molecules, and more. Already, Webb observations have resulted in hundreds of scientific papers answering longstanding questions and raising new ones to address with Webb.

The breadth of Webb science is also apparent in its observations of the region of space we are most familiar with -- our own solar system. Faint rings of gas giants appear out of the darkness, dotted by moons, while in the background Webb shows distant galaxies. By comparing detections of water and other molecules in our solar system with those found in the disks of other, much younger planetary systems, Webb is helping to build up clues about our own origins -- how Earth became the ideal place for life as we know it.

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'Taffy galaxies' collide, leave behind bridge of star-forming material

Galaxy collisions are transformative events, largely responsible for driving the evolution of the Universe. The mixing and mingling of stellar material is an incredibly dynamic process that can lead to the formation of molecular clouds populated with newly forming stars. But, a head-on collision between the two galaxies UGC 12914 (left) and UGC 12915 (right) 25-30 million years ago appears to have resulted in a different kind of structure -- a bridge of highly turbulent material spanning the two galaxies. Though this intergalactic bridge is teeming with star-forming material, its turbulent nature is suppressing star formation.

This pair of galaxies, nicknamed the Taffy Galaxies, is located about 180 million light-years away in the direction of the constellation Pegasus.

This new image, captured with Gemini North, one half of the International Gemini Observatory, operated by NSF's NOIRLab, showcases the fascinating feature that gave them their name. A tenuous bridge composed of narrow molecular filaments, shown in brown, and clumps of hydrogen gas, shown in red, can be seen between the two galaxies. Its complex web structure resembles taffy being stretched as the pair slowly separates.

Galaxy collisions can happen out of a variety of different scenarios, often involving a larger galaxy and a smaller satellite galaxy. As they drift near one another, the satellite galaxy can attract one of the larger galaxy's primary spiral arms, pulling it out of its orbit. Or the satellite galaxy can actually intersect with the larger galaxy, causing significant distortions to its own structure. In other cases, a collision can lead to a merger if neither member has enough momentum to continue on after colliding. In all these scenarios, stellar material from both galaxies mixes through a gradual combining and redistribution of gas, like two puddles of liquid that are slowly bleeding into each other. The resulting collecting and compression of the gas can then trigger star formation.

A head-on collision, however, would be more like pouring liquid from two separate cups into a shared bowl. When the Taffy Galaxies' collided, their galactic disks and gaseous components smashed right into each other. This resulted in a massive injection of energy into the gas, causing it to become highly turbulent. As the pair emerged from their collision, high-velocity gas was pulled from each galaxy, creating a massive gas bridge between them. The turbulence of the stellar material throughout the bridge is now prohibiting the collection and compression of gas that are required to form new stars.

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A star is born: Nearby galaxies provide clues about star formation

It is a popular notion that aside from large celestial objects like planets, stars and asteroids, outer space is empty. In fact, galaxies are filled with something called the interstellar medium (ISM) -- that is, the gas and dust that permeate the space in between those large objects. Importantly, under the right conditions, it is from the ISM that new stars are formed.

Now researchers from the University of California San Diego, in collaboration with a worldwide project team, have released their findings in a special issue of The Astrophysical Journal Letters dedicated to their work using advanced telescope images through the JWST Cycle 1 Treasury Program.

"With JWST, you can make incredible maps of nearby galaxies at very high resolution that provide amazingly detailed images of the interstellar medium," stated Associate Professor of Physics Karin Sandstrom who is a co-principal investigator on the project.

Although JWST can look at very distant galaxies, the ones Sandstrom's group studied are relatively close at about 30 million light years away, including one known as the Phantom Galaxy. Also known as M74 or NGC 628, astronomers have known of the Phantom Galaxy's existence since at least the 18th century.

Sandstrom, along with postdoctoral scholar Jessica Sutter and former postdoctoral scholar Jeremy Chastenet (now at University of Ghent), focused on a specific component of the ISM called polycyclic aromatic hydrocarbons (PAHs). PAHs are small particles of dust -- the size of a molecule -- and it's their small size that makes them so valuable to researchers.

When PAHs absorb a photon from a star, they vibrate and produce emission features that can be detected in the mid-infrared electromagnetic spectrum -- something that typically doesn't happen with larger dust grains from the ISM. The vibrational features of PAHs allow researchers to observe many important characteristics including size, ionization and structure.

This is something Sandstrom has been interested in since graduate school. "The Spitzer Space Telescope looked at the mid-infrared and that's what I used in my Ph.D. thesis. Since Spitzer was retired, we haven't had much access to the mid-infrared spectrum, but JWST is incredible," she stated. "Spitzer had a mirror that was 0.8 meters; JWST's mirror is 6.5 meters. It's a huge telescope and it has amazing instruments. I've been waiting a very long time for this."

Even though PAHs are not by mass a big fraction of the overall ISM, they're important because they're easily ionized -- a process that can produce photoelectrons which heat the rest of the gas in the ISM. A better understanding of PAHs will lead to a better understanding of the physics of the ISM and how it operates. Astrophysicists are hopeful JWST can provide a view into how PAHs are formed, how they change and how they're destroyed.

Because PAHs are evenly distributed throughout the ISM, they allow researchers to see not just the PAHs themselves, but everything around them as well. Previous maps, such as ones taken by Spitzer, contained much less detail -- they essentially looked like galactic blobs. With the clarity JWST provides, astrophysicists can now see gas filaments and even "bubbles" blown by newly formed stars, whose intense radiation fields and resulting supernova evaporate the gas clouds around them.

To get observation time on JWST, the Cycle 1 Treasury Program team had to design observations that included details such as exposure length and filters. Once their submission was accepted, Space Telescope Science Institute, which is responsible for the science and mission operations for JWST, captures and processes the data. This program includes data from 19 galaxies in total.

The Cycle 1 Treasury Program is part of a bigger project called PHANGS (Physics at High Angular Resolution in Nearby GalaxieS). PHANGS studies star formation and the ISM using multi-wavelength images from the Atacama Large Millimeter Array (ALMA) and the Very Large Telescope, both in Chile. However, because the dense clouds in which star formation happens contain a lot of dust, it is difficult for optical light to penetrate to see what's happening inside. Using the mid-infrared spectrum allows researchers to use that same dust and its bright emission to get high-resolution, detailed images.

"One of the things I'm most excited about is now that we have this high-resolution tracer of the ISM, we can map all kinds of things, including the structure of the diffuse gas, which has to become denser and molecular for star formation to occur," said Sandstrom. "We can also map the gas surrounding newly formed stars where there is a lot of 'feedback' such as from supernova explosions. We really get to see the whole cycle of the ISM in a lot of detail. That is the core of how a galaxy is going to form stars."

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Astrophysics: Scientists observe high-speed star formation

Even though SOFIA is no longer in operation, the data collected so far are essential for basic astronomical research because there is no longer an instrument that extensively maps the sky in this wavelength range (typically 60 to 200 micrometres). The now active James Webb Space Telescope observes in the infrared at shorter wavelengths and focuses on spatially small areas. Therefore, the analysis of the data collected by SOFIA is ongoing and continues to provide important insights – also regarding other star-forming regions: “In the list of FEEDBACK sources, there are other gas clouds in different stages of evolution, where we are now looking for the weak CII radiation at the peripheries of the clouds to detect similar interactions as in the Cygnus X region,” Schneider concluded.

al standards. The results of the study ‘Ionized carbon as a tracer for the assembly of interstellar clouds’ will appear in the next issue of Nature Astronomy.

The observations were carried out in an international project led by Dr Nicola Schneider at the University of Cologne and Prof Alexander Tielens at the University of Maryland as part of the FEEDBACK programme on board the flying observatory SOFIA (Stratospheric Observatory for Infrared Astronomy). The new findings modify previous perceptions that this specific process of star formation is quasi-static and quite slow. The dynamic formation process now observed would also explain the formation of particularly massive stars.

By comparing the distribution of ionized carbon, molecular carbon monoxide and atomic hydrogen, the team found that the shells of interstellar gas clouds are made of hydrogen and collide with each other at speeds of up to twenty kilometres per second. “This high speed compresses the gas into denser molecular regions where new, mainly massive stars form. We needed the CII observations to detect this otherwise ‘dark’ gas,” said Dr Schneider. The observations show for the first time the faint CII radiation from the periphery of the clouds, which could not be observed before. Only SOFIA and its sensitive instruments were capable of detecting this radiation.

SOFIA was operated by NASA and the German Aerospace Center (DLR) until September 2022. The observatory consisted of a converted Boeing 747 with a built-in 2.7-metre telescope. It was coordinated by the German SOFIA Institute (DSI) and the Universities Space Research Association (USRA). SOFIA observed the sky from the stratosphere (above 13 kilometres) and covered the infrared region of the electromagnetic spectrum, just beyond what humans can see. The Boeing thus flew above most of the water vapour in the Earth’s atmosphere, which otherwise blocks out infrared light. This allowed the scientists to observe a wavelength range that is not accessible from Earth. For the current results, the team used the upGREAT receiver installed on SOFIA in 2015 by the Max Planck Institute for Radio Astronomy in Bonn and the University of Cologne.

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NASA's Webb uncovers star formation in cluster's dusty ribbons

NGC 346, one of the most dynamic star-forming regions in nearby galaxies, is full of mystery. Now, it is less mysterious with new findings from NASA's James Webb Space Telescope.

NCG 346 is located in the Small Magellanic Cloud (SMC), a dwarf galaxy close to our Milky Way. The SMC contains lower concentrations of elements heavier than hydrogen or helium, which astronomers call metals, compared to the Milky Way. Since dust grains in space are composed mostly of metals, scientists expected there would be low amounts of dust, and that it would be hard to detect. New data from Webb reveals the opposite.

Astronomers probed this region because the conditions and amount of metals within the SMC resemble those seen in galaxies billions of years ago, during an era in the universe known as "cosmic noon," when star formation was at its peak. Some 2 to 3 billion years after the big bang, galaxies were forming stars at a furious rate. The fireworks of star formation happening then still shape the galaxies we see around us today.

"A galaxy during cosmic noon wouldn't have one NGC 346 like the Small Magellanic Cloud does; it would have thousands" of star-forming regions like this one, said Margaret Meixner, an astronomer at the Universities Space Research Association and principal investigator of the research team. "But even if NGC 346 is now the one and only massive cluster furiously forming stars in its galaxy, it offers us a great opportunity to probe conditions that were in place at cosmic noon."

By observing protostars still in the process of forming, researchers can learn if the star formation process in the SMC is different from what we observe in our own Milky Way. Previous infrared studies of NGC 346 have focused on protostars heavier than about 5 to 8 times the mass of our Sun. "With Webb, we can probe down to lighter-weight protostars, as small as one tenth of our Sun, to see if their formation process is affected by the lower metal content," said Olivia Jones of the United Kingdom Astronomy Technology Centre, Royal Observatory Edinburgh, a co-investigator on the program.

As stars form, they gather gas and dust, which can look like ribbons in Webb imagery, from the surrounding molecular cloud. The material collects into an accretion disk that feeds the central protostar. Astronomers have detected gas around protostars within NGC 346, but Webb's near-infrared observations mark the first time they have also detected dust in these disks.

"We're seeing the building blocks, not only of stars, but also potentially of planets," said Guido De Marchi of the European Space Agency, a co-investigator on the research team. "And since the Small Magellanic Cloud has a similar environment to galaxies during cosmic noon, it's possible that rocky planets could have formed earlier in the universe than we might have thought."

The team also has spectroscopic observations from Webb's NIRSpec instrument that they are continuing to analyze. These data are expected to provide new insights into the material accreting onto individual protostars, as well as the environment immediately surrounding the protostar.

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NASA's Webb catches fiery hourglass as new star forms

NASA's James Webb Space Telescope has revealed the once-hidden features of the protostar within the dark cloud L1527, providing insight into the beginnings of a new star. These blazing clouds within the Taurus star-forming region are only visible in infrared light, making it an ideal target for Webb's Near-Infrared Camera (NIRCam).

The protostar itself is hidden from view within the "neck" of this hourglass shape. An edge-on protoplanetary disk is seen as a dark line across the middle of the neck. Light from the protostar leaks above and below this disk, illuminating cavities within the surrounding gas and dust.

The region's most prevalent features, the clouds colored blue and orange in this representative-color infrared image, outline cavities created as material shoots away from the protostar and collides with surrounding matter. The colors themselves are due to layers of dust between Webb and the clouds. The blue areas are where the dust is thinnest. The thicker the layer of dust, the less blue light is able to escape, creating pockets of orange.

Webb also reveals filaments of molecular hydrogen that have been shocked as the protostar ejects material away from it. Shocks and turbulence inhibit the formation of new stars, which would otherwise form all throughout the cloud. As a result, the protostar dominates the space, taking much of the material for itself.

Despite the chaos that L1527 causes, it's only about 100,000 years old -- a relatively young body. Given its age and its brightness in far-infrared light as observed by missions like the Infrared Astronomical Satellite, L1527 is considered a class 0 protostar, the earliest stage of star formation. Protostars like these, which are still cocooned in a dark cloud of dust and gas, have a long way to go before they become full-fledged stars. L1527 doesn't generate its own energy through nuclear fusion of hydrogen yet, an essential characteristic of stars. Its shape, while mostly spherical, is also unstable, taking the form of a small, hot, and puffy clump of gas somewhere between 20 and 40% the mass of our Sun.

As the protostar continues to gather mass, its core gradually compresses and gets closer to stable nuclear fusion. The scene shown in this image reveals L1527 doing just that. The surrounding molecular cloud is made up of dense dust and gas being drawn to the center, where the protostar resides. As the material falls in, it spirals around the center. This creates a dense disk of material, known as an accretion disk, which feeds material to the protostar. As it gains more mass and compresses further, the temperature of its core will rise, eventually reaching the threshold for nuclear fusion to begin.

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ALMA witnesses deadly star-slinging tug-of-war between merging galaxies

While observing a newly-dormant galaxy using the Atacama Large Millimeter/submillimeter Array (ALMA) and the Hubble Space Telescope (HST), scientists discovered that it had stopped forming stars not because it had used up all of its gas but because most of its star-forming fuel had been thrown out of the system as it merged with another galaxy. The result is a first for ALMA scientists. What's more, if proven common, the results could change the way scientists think about galaxy mergers and deaths. The results of the research are published in The Astrophysical Journal Letters.

As galaxies move through the Universe, they sometimes encounter other galaxies. As they interact, each galaxy's gravity pulls on the other. The ensuing tug-of-war flings gas and stars away from the galaxies, leaving behind streams of material known as tidal tails.

And that's just what scientists believe happened to SDSS J1448+1010, but with a plot twist. The massive galaxy, which was born when the Universe was about half its current age, has nearly completed merging with another galaxy. During observations with the HST and ALMA -- an international collaboration in which the U.S. National Science Foundation's National Radio Astronomy Observatory (NRAO) is a partner -- scientists discovered tidal tails containing roughly half of the entire system's cold, star-forming gas. The discovery of the forcefully discarded material -- equal to 10 billion times the mass of Earth's Sun -- was an indication that the merger may be responsible for snuffing out star formation, and that's something scientists didn't expect.

"What initially made this massive galaxy interesting was that, for some reason, it suddenly stopped forming stars about 70 million years ago immediately following a burst of star-forming activity. Most galaxies are happy to just keep forming stars," said Justin Spilker, an astronomer at Texas A&M University and the lead author of the paper. "Our observations with ALMA and Hubble proved that the real reason the galaxy stopped forming stars is that the merger process ejected about half the gas fuel for star formation into intergalactic space. With no fuel, the galaxy couldn't keep forming stars."

The discovery is shedding light on the processes by which galaxies live or die, and helping scientists to better understand their evolution.

"When we look out at the Universe, we see some galaxies that are actively forming new stars, like our own Milky Way, and some that aren't. But those 'dead' galaxies have many old stars in them, so they must have formed all of those stars at some point and then stopped making new ones," said Wren Suess, a cosmology fellow at the University of California Santa Cruz and a co-author of the paper. "We still don't yet understand all of the processes that make galaxies stop forming stars, but this discovery shows just how powerful these major galaxy mergers are, and how much they can affect how a galaxy grows and changes over time."

Because the new result is from a single observation, it is currently unclear just how common this tug-of-war and its resultant quiescence may be. However, the discovery challenges long-held theories about exactly how star formation stops and galaxies die and has provided scientists with an exciting new challenge: to find more examples.

"While it's pretty clear from this system that cold gas really can end up way outside of a merger system that shuts off a galaxy, the sample size of one galaxy tells us very little about how common this process is," said David Setton, a graduate student in the department of physics and astronomy at the University of Pittsburgh and a co-author of the paper. "But, there are many galaxies out there like J1448+1010 that we're able to catch right in the middle of those crashes and study exactly what happens to them when they go through that stage. The ejection of cold gas is an exciting new piece of the quiescence puzzle, and we're excited to try to find more examples of this."

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Stars determine their own masses

Last year, a team of astrophysicists including key members from Northwestern University launched STARFORGE, a project that produces the most realistic, highest-resolution 3D simulations of star formation to date. Now, the scientists have used the highly detailed simulations to uncover what determines the masses of stars, a mystery that has captivated astrophysicists for decades.

In a new study, the team discovered that star formation is a self-regulatory process. In other words, stars themselves set their own masses. This helps explain why stars formed in disparate environments still have similar masses. The new finding may enable researchers to better understand star formation within our own Milky Way and other galaxies.

The study was published last week in the Monthly Notices of the Royal Astronomical Society. The collaborative team included experts from Northwestern, University of Texas at Austin (UT Austin), Carnegie Observatories, Harvard University and the California Institute of Technology. The lead author of the new study is Dávid Guszejnov, a postdoctoral fellow at UT Austin.

"Understanding the stellar initial mass function is such an important problem because it impacts astrophysics across the board -- from nearby planets to distant galaxies," said Northwestern's Claude-André Faucher-Giguère, a study co-author. "This is because stars have relatively simple DNA. If you know the mass of a star, then you know most things about the star: how much light it emits, how long it will live and what will happen to it when it dies. The distribution of stellar masses is thus critical for whether planets that orbit stars can potentially sustain life, as well as what distant galaxies look like."

Faucher-Giguère is an associate professor of physics and astronomy in Northwestern's Weinberg College of Arts and Sciences and a member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA).

Outer space is filled with giant clouds, consisting of cold gas and dust. Slowly, gravity pulls far-flung specks of this gas and dust toward each other to form dense clumps. Materials in these clumps fall inward, crashing and sparking heat to create a newborn star.

Surrounding each of these "protostars" is a rotating disk of gas and dust. Every planet in our solar system was once specks in such a disk around our newborn sun. Whether or not planets orbiting a star could host life is dependent on the mass of the star and how it formed. Therefore, understanding star formation is crucial to determining where life can form in the universe.

"Stars are the atoms of the galaxy," said Stella Offner, associate professor of astronomy at UT Austin. "Their mass distribution dictates whether planets will be born and if life might develop."

Every subfield in astronomy depends on the mass distribution of stars -- or initial mass function (IMF) -- which has proved challenging for scientists to model correctly. Stars much bigger than our sun are rare, making up only 1% of newborn stars. And, for every one of these stars there are up to 10 sun-like stars and 30 dwarf stars. Observations found that no matter where we look in the Milky Way these ratios (i.e., the IMF) are the same, for both newly formed star clusters and for those that are billions of years old.

This is the mystery of the IMF. Every population of stars in our galaxy, and in all the dwarf galaxies that surround us, has this same balance -- even though their stars were born under wildly different conditions over billions of years. In theory, the IMF should vary dramatically, but it is virtually universal, which has puzzled astronomers for decades.

"For a long time, we have been asking why," Guszejnov said. "Our simulations followed stars from birth to the natural endpoint of their formation to solve this mystery."

The new simulations, however, showed that stellar feedback, in an effort to oppose gravity, pushes stellar masses toward the same mass distribution. These simulations are the first to follow the formation of individual stars in a collapsing giant cloud, while also capturing how these newly formed stars interact with their surroundings by giving off light and shedding mass via jets and winds -- a phenomenon referred to as "stellar feedback."

The STARFORGE project is a multi-institutional initiative, co-led by Guszejnov and Michael Grudić of Carnegie Observatories. Grudić was a CIERA postdoctoral fellow at Northwestern when the project was initiated. STARFORGE simulations are the first to simultaneously model star formation, evolution and dynamics while accounting for stellar feedback, including jets, radiation, wind and nearby supernovae activity. While other simulations have incorporated individual types of stellar feedback, STARFORGE puts them all together to simulate how these various processes interact to affect star formation.

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Webb captures stellar gymnastics in the Cartwheel Galaxy

NASA's James Webb Space Telescope has peered into the chaos of the Cartwheel Galaxy, revealing new details about star formation and the galaxy's central black hole. Webb's powerful infrared gaze produced a detailed image of the Cartwheel and two smaller companion galaxies against a backdrop of many other galaxies. The image provides a new view of how the Cartwheel Galaxy has changed over billions of years.

The Cartwheel Galaxy, located about 500 million light-years away in the Sculptor constellation, is a rare sight. Its appearance, much like that of the wheel of a wagon, is the result of an intense event -- a high-speed collision between a large spiral galaxy and a smaller galaxy not visible in this image. Collisions of galactic proportions cause a cascade of different, smaller events between the galaxies involved; the Cartwheel is no exception.

The collision most notably affected the galaxy's shape and structure. The Cartwheel Galaxy sports two rings -- a bright inner ring and a surrounding, colorful ring. These two rings expand outwards from the center of the collision, like ripples in a pond after a stone is tossed into it. Because of these distinctive features, astronomers call this a "ring galaxy," a structure less common than spiral galaxies like our Milky Way.

The bright core contains a tremendous amount of hot dust with the brightest areas being the home to gigantic young star clusters. On the other hand, the outer ring, which has expanded for about 440 million years, is dominated by star formation and supernovas. As this ring expands, it plows into surrounding gas and triggers star formation.

Other telescopes, including the Hubble Space Telescope, have previously examined the Cartwheel. But the dramatic galaxy has been shrouded in mystery -- perhaps literally, given the amount of dust that obscures the view. Webb, with its ability to detect infrared light, now uncovers new insights into the nature of the Cartwheel.

The Near-Infrared Camera (NIRCam), Webb's primary imager, looks in the near-infrared range from 0.6 to 5 microns, seeing crucial wavelengths of light that can reveal even more stars than observed in visible light. This is because young stars, many of which are forming in the outer ring, are less obscured by the presence of dust when observed in infrared light. In this image, NIRCam data are colored blue, orange, and yellow. The galaxy displays many individual blue dots, which are individual stars or pockets of star formation. NIRCam also reveals the difference between the smooth distribution or shape of the older star populations and dense dust in the core compared to the clumpy shapes associated with the younger star populations outside of it.

Learning finer details about the dust that inhabits the galaxy, however, requires Webb's Mid-Infrared Instrument (MIRI). MIRI data are colored red in this composite image. It reveals regions within the Cartwheel Galaxy rich in hydrocarbons and other chemical compounds, as well as silicate dust, like much of the dust on Earth. These regions form a series of spiraling spokes that essentially form the galaxy's skeleton. These spokes are evident in previous Hubble observations released in 2018, but they become much more prominent in this Webb image.

Webb's observations underscore that the Cartwheel is in a very transitory stage. The galaxy, which was presumably a normal spiral galaxy like the Milky Way before its collision, will continue to transform. While Webb gives us a snapshot of the current state of the Cartwheel, it also provides insight into what happened to this galaxy in the past and how it will evolve in the future.

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Supermassive blackhole influences star formation

A European team of astronomers led by Professor Kalliopi Dasyra of the National and Kapodistrian University of Athens, Greece, under participation of Dr. Thomas Bisbas, University of Cologne modelled several emission lines in Atacama Large Millimeter Array (ALMA) and Very Large Telescope (VLT) observations to measure the gas pressure in both jet-impacted clouds and ambient clouds. With these unprecedented measurements, published recently in Nature Astronomy, they discovered that the jets significantly change the internal and external pressure of molecular clouds in their path. Depending on which of the two pressures changes the most, both compression of clouds and triggering of star formation and dissipation of clouds and delaying of star formation are possible in the same galaxy. "Our results show that supermassive black holes, even though they are located at the centers of galaxies, could affect star formation in a galaxy-wide manner" said Professor Dasyra, adding that "studying the impact of pressure changes in the stability of clouds was key to the success of this project. Once few stars actually form in a wind, it is usually very hard to detect their signal on top of the signal of all other stars in the galaxy hosting the wind."

It is believed that supermassive black holes lie at the centers of most galaxies in our Universe. When particles that were infalling onto these black holes are trapped by magnetic fields, they can be ejected outwards and travel far inside galaxies in the form of enormous and powerful jets of plasma. These jets are often perpendicular to galactic disks. In IC 5063 however, a galaxy 156 million light years away, the jets are actually propagating within the disk, interacting with cold and dense molecular gas clouds. From this interaction, compression of jet-impacted clouds is theorized to be possible, leading to gravitational instabilities and eventually star formation due to the gas condensation.

For the experiment, the team used the emission of carbon monoxide (CO) and formyl cation (HCO+) provided by ALMA, and the emission of ionized sulfur and ionized nitrogen provided by VLT. They then used advanced and innovative astrochemical algorithms to pinpoint the environmental conditions in the outflow and in the surrounding medium. These environmental conditions contain information about the strength of the far-ultraviolet radiation of stars, the rate at which relativistic charged particles ionize the gas, and the mechanical energy deposited on the gas by the jets. Narrowing down these conditions revealed the densities and gas temperatures descriptive of different parts of this galaxy, which were then used to provide pressures.

"We have performed many thousands of astrochemical simulations to cover a wide range of possibilities that may exist in IC 5063" said co-author Dr. Thomas Bisbas, DFG Fellow of the University of Cologne and former postdoctoral researcher at the National Observatory of Athens. A challenging part of the work was to meticulously identify as many physical constraints as possible to the examined range that each parameter could have. "This way, we could get the optimal combination of physical parameters of clouds at different locations of the galaxy," said co-author Mr. Georgios Filippos Paraschos, Ph.D. student at the Max Planck Institute for Radio Astronomy in Bonn and former Master's student at the National and Kapodistrian University of Athens.

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An ocean of galaxies awaits

Sometime around 400 million years after the birth of our universe, the first stars began to form. The universe's so-called dark ages came to an end and a new light-filled era began. More and more galaxies began to take shape and served as factories for churning out new stars, a process that reached a peak about 4 billion years after the Big Bang.

Luckily for astronomers, this bygone era can be observed. Distant light takes time to reach us, and our telescopes can pick up light emitted by galaxies and stars billions of years ago (our universe is 13.8 billion years old). But the details of this chapter in our universe's history are murky since most of the stars being formed are faint and hidden by dust.

A new Caltech project, called COMAP (CO Mapping Array Project), will offer us a new glimpse into this epoch of galaxy assembly, helping to answer questions about what really caused the universe's rapid increase in the production of stars.

"Most instruments might see the tip of an iceberg when looking at galaxies from this period," says Kieran Cleary, the project's principal investigator and the associate director of Caltech's Owens Valley Radio Observatory (OVRO). "But COMAP will see what lies underneath, hidden from view."

The current phase of the project uses a 10.4-meter "Leighton" radio dish at OVRO to study the most common kinds of star-forming galaxies spread across space and time, including those that are too difficult to view in other ways because they are too faint or hidden by dust. The radio observations trace the raw material from which stars are made: cold hydrogen gas. This gas is not easy to pinpoint directly, so instead COMAP measures bright radio signals from carbon monoxide (CO) gas, which is always present along with the hydrogen. COMAP's radio camera is the most powerful ever built to detect these radio signals.

The first science results from the project have just been published in seven papers in The Astrophysical Journal. Based on observations taken one year into a planned five-year survey, COMAP set upper limits on how much cold gas must be present in galaxies at the epoch being studied, including the ones that are normally too faint and dusty to see. While the project has not yet made a direct detection of the CO signal, these early results demonstrate that it is on track to do so by the end of the initial five-year survey and ultimately will paint the most comprehensive picture yet of the universe's history of star formation.

"Looking to the future of the project, we aim to use this technique to successively look further and further back in time," Cleary says. "Starting 4 billion years after the Big Bang, we will keep pushing back in time until we reach the epoch of the first stars and galaxies, a couple of billion years earlier."

Anthony Readhead, the co-principal investigator and the Robinson Professor of Astronomy, Emeritus, says that COMAP will see the not only the first epoch of stars and galaxies, but also their epic decline. "We will observe star formation rising and falling like an ocean tide," he says.

COMAP works by capturing blurry radio images of clusters of galaxies over cosmic time rather than sharp images of individual galaxies. This blurriness enables the astronomers to efficiently catch all the radio light coming from a larger pool of galaxies, even the faintest and dustiest ones that have never been seen.

"In this way, we can find the average properties of typical, faint galaxies without needing to know very precisely where any individual galaxy is located," explains Cleary. "This is like finding the temperature of a large volume of water using a thermometer rather than analyzing the motions of the individual water molecules."

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Researchers use galaxy as a 'cosmic telescope' to study heart of the young universe

A unique new instrument, coupled with a powerful telescope and a little help from nature, has given researchers the ability to peer into galactic nurseries at the heart of the young universe.

After the big bang some 13.8 billion years ago, the early universe was filled with enormous clouds of neutral diffuse gas, known as Damped Lyman-α systems, or DLAs. These DLAs served as galactic nurseries, as the gasses within slowly condensed to fuel the formation of stars and galaxies. They can still be observed today, but it isn't easy.

"DLAs are a key to understanding how galaxies form in the universe, but they are typically difficult to observe since the clouds are too diffuse and don't emit any light themselves," says Rongmon Bordoloi, assistant professor of physics at North Carolina State University and corresponding author of the research.

Currently, astrophysicists use quasars -- supermassive black holes that emit light -- as "backlight" to detect the DLA clouds. And while this method does allow researchers to pinpoint DLA locations, the light from the quasars only acts as small skewers through a massive cloud, hampering efforts to measure their total size and mass.

But Bordoloi and John O'Meara, chief scientist at the W.M. Keck Observatory in Kamuela, Hawaii, found a way around the problem by using a gravitationally lensed galaxy and integral field spectroscopy to observe two DLAs -- and the host galaxies within -- that formed around 11 billion years ago, not long after the big bang.

"Gravitationally lensed galaxies refers to galaxies that appear stretched and brightened," Bordoloi says. "This is because there is a gravitationally massive structure in front of the galaxy that bends the light coming from it as it travels toward us. So we end up looking at an extended version of the object -- it's like using a cosmic telescope that increases magnification and gives us better visualization.

"The advantage to this is twofold: One, the background object is extended across the sky and bright, so it is easy to take spectrum readings on different parts of the object. Two, because lensing extends the object, you can probe very small scales. For example, if the object is one light year across, we can study small bits in very high fidelity."

Spectrum readings allow astrophysicists to "see" elements in deep space that are not visible to the naked eye, such as diffuse gaseous DLAs and the potential galaxies within them. Normally, gathering the readings is a long and painstaking process. But the team solved that issue by performing integral field spectroscopy with the Keck Cosmic Web Imager.

Integral field spectroscopy allowed the researchers to obtain a spectrum at every single pixel on the part of the sky it targeted, making spectroscopy of an extended object on the sky very efficient. This innovation combined with the stretched and brightened gravitationally lensed galaxy allowed the team to map out the diffuse DLA gas in the sky at high fidelity. Through this method the researchers were able to determine not only the size of the two DLAs, but also that they both contained host galaxies.

"I've waited most of my career for this combination: a telescope and instrument powerful enough, and nature giving us a bit of lucky alignments to study not one but two DLAs in a rich new way," O'Meara says. "It's great to see the science come to fruition."

The DLAs are huge, by the way. With diameters greater than 17.4 kiloparsecs, they're more than two thirds the size of the Milky Way galaxy today. For comparison, 13 billion years ago, a typical galaxy would have a diameter of less than 5 kiloparsecs. A parsec is 3.26 light years, and a kiloparsec is 1,000 parsecs, so it would take light about 56,723 years to travel across each DLA.

"But to me, the most amazing thing about the DLAs we observed is that they aren't unique -- they seem to have similarities in structure, host galaxies were detected in both, and their masses indicate that they contain enough fuel for the next generation of star formation," Bordoloi says. "With this new technology at our disposal, we are going to be able to dig deeper into how stars formed in the early universe."

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Scientists find elusive gas from post-starburst galaxies hiding in plain sight

Post-starburst galaxies were previously thought to scatter all of their gas and dust -- the fuel required for creating new stars -- in violent bursts of energy, and with extraordinary speed. Now, new data from the Atacama Large Millimeter/submillimeter Array (ALMA) reveals that these galaxies don't scatter all of their star-forming fuel after all. Instead, after their supposed end, these dormant galaxies hold onto and compress large amounts of highly-concentrated, turbulent gas. But contrary to expectation, they're not using it to form stars.

In most galaxies, scientists expect gas to be distributed in a way similar to starlight. But for post-starburst galaxies, or PSBs, this isn't the case. PSBs are different from other galaxies because they are born in the aftermath of violent collisions, or mergers between galaxies. Galaxy mergers typically trigger massive bursts of star formation, but in PSBs, this outburst slows down and near-completely stops almost as soon as it begins. As a result, scientists previously believed that little or no star-forming fuel was left in these galaxies' central star-forming factories. And until now, the belief was that the molecular gases had been redistributed to radii well beyond the galaxies, either through stellar processes or by the effects of black holes. The new results challenge this theory.

"We've known for some time that large amounts of molecular gas remains in the vicinity of PSBs but haven't been able to say where, which in turn, has prevented us from understanding why these galaxies stopped forming stars. Now, we have discovered a considerable amount of remaining gas within the galaxies and that remaining gas is very compact," said Adam Smercina, an astronomer at the University of Washington and the principal investigator of the study. "While this compact gas should be forming stars efficiently, it isn't. In fact, it is less than 10-percent as efficient as similarly compact gas is expected to be."

In addition to being compact enough to make stars, the gas in the observed dormant -- or quiescent -- galaxies had another surprise in store for the team: it was often centrally-located, though not always, and was surprisingly turbulent. Combined, these two characteristics led to more questions than answers for researchers.

"The rates of star formation in the PSBs we observed are much lower than in other galaxies, even though there appears to be plenty of fuel to sustain the process," said Smercina. "In this case, star formation may be suppressed due to turbulence in the gas, much like a strong wind can suppress a fire. However, star formation can also be enhanced by turbulence, just like wind can fan flames, so understanding what is generating this turbulent energy, and how exactly it is contributing to dormancy, is a remaining question of this work."

Decker French, an astronomer at the University of Illinois, and a co-author of the research added, "These results raise the question of what energy sources are present in these galaxies to drive turbulence and prevent the gas from forming new stars. One possibility is energy from the accretion disk of the central supermassive black holes in these galaxies."

A clear understanding of the processes that govern the formation of stars and galaxies is key to providing context to the Universe and our place in it. The discovery of turbulent, compact gas in otherwise dormant galaxies gives researchers one more clue to solving the mystery of how galaxies in particular live, evolve and die over the course of billions of years. And that means additional future research with the help of ALMA's 1.3mm receiver, which sees the otherwise invisible with stark clarity.

J.D. Smith, an astronomer at the University of Toledo, and a co-author of the research said, "There is much about the evolution of a typical galaxy we don't understand, and the transition from their vibrant star-forming lives into quiescence is one of the least understood periods. Although post-starbursts were very common in the early Universe, today they are quite rare. This means the nearest examples are still hundreds of millions of light-years away, but these events foreshadow the potential outcome of a collision, or merger, between the Milky Way Galaxy and the Andromeda Galaxy several billion years from now. Only with the incredible resolving power of ALMA could we peer deep into the molecular reservoirs left behind 'after the fall.'"

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Hubble finds a black hole igniting star formation in a dwarf galaxy

Often portrayed as destructive monsters that hold light captive, black holes take on a less villainous role in the latest research from NASA's Hubble Space Telescope. A black hole at the heart of the dwarf galaxy Henize 2-10 is creating stars rather than gobbling them up. The black hole is apparently contributing to the firestorm of new star formation taking place in the galaxy. The dwarf galaxy lies 30 million light-years away, in the southern constellation Pyxis.

A decade ago this small galaxy set off debate among astronomers as to whether dwarf galaxies were home to black holes proportional to the supermassive behemoths found in the hearts of larger galaxies. This new discovery has little Henize 2-10, containing only one-tenth the number of stars found in our Milky Way, poised to play a big part in solving the mystery of where supermassive black holes came from in the first place.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

"Ten years ago, as a graduate student thinking I would spend my career on star formation, I looked at the data from Henize 2-10 and everything changed," said Amy Reines, who published the first evidence for a black hole in the galaxy in 2011 and is the principal investigator on the new Hubble observations, published in the January 19 issue of Nature.

"From the beginning I knew something unusual and special was happening in Henize 2-10, and now Hubble has provided a very clear picture of the connection between the black hole and a neighboring star forming region located 230 light-years from the black hole," Reines said.

That connection is an outflow of gas stretching across space like an umbilical cord to a bright stellar nursery. The region was already home to a dense cocoon of gas when the low-velocity outflow arrived. Hubble spectroscopy shows the outflow was moving about 1 million miles per hour, slamming into the dense gas like a garden hose hitting a pile of dirt and spreading out. Newborn star clusters dot the path of the outflow's spread, their ages also calculated by Hubble.

This is the opposite effect of what's seen in larger galaxies, where material falling toward the black hole is whisked away by surrounding magnetic fields, forming blazing jets of plasma moving at close to the speed of light. Gas clouds caught in the jets' path would be heated far beyond their ability to cool back down and form stars. But with the less-massive black hole in Henize 2-10, and its gentler outflow, gas was compressed just enough to precipitate new star formation.

"At only 30 million light-years away, Henize 2-10 is close enough that Hubble was able to capture both images and spectroscopic evidence of a black hole outflow very clearly. The additional surprise was that, rather than suppressing star formation, the outflow was triggering the birth of new stars," said Zachary Schutte, Reines' graduate student and lead author of the new study.

Ever since her first discovery of distinctive radio and X-ray emissions in Henize 2-10, Reines has thought they likely came from a massive black hole, but not as supermassive as those seen in larger galaxies. Other astronomers, however, thought that the radiation was more likely being emitted by a supernova remnant, which would be a familiar occurrence in a galaxy that is rapidly pumping out massive stars that quickly explode.

"Hubble's amazing resolution clearly shows a corkscrew-like pattern in the velocities of the gas, which we can fit to the model of a precessing, or wobbling, outflow from a black hole. A supernova remnant would not have that pattern, and so it is effectively our smoking-gun proof that this is a black hole," Reines said.

Reines expects that even more research will be directed at dwarf galaxy black holes in the future, with the aim of using them as clues to the mystery of how supermassive black holes came to be in the early universe. It's a persistent puzzle for astronomers. The relationship between the mass of the galaxy and its black hole can provide clues. The black hole in Henize 2-10 is around 1 million solar masses. In larger galaxies, black holes can be more than 1 billion times our Sun's mass. The more massive the host galaxy, the more massive the central black hole.

Current theories on the origin of supermassive black holes break down into three categories: 1) they formed just like smaller stellar-mass black holes, from the implosion of stars, and somehow gathered enough material to grow supermassive, 2) special conditions in the early universe allowed for the formation of supermassive stars, which collapsed to form massive black hole "seeds" right off the bat, or 3) the seeds of future supermassive black holes were born in dense star clusters, where the cluster's overall mass would have been enough to somehow create them from gravitational collapse.

So far, none of these black hole seeding theories has taken the lead. Dwarf galaxies like Henize 2-10 offer promising potential clues, because they have remained small over cosmic time, rather than undergoing the growth and mergers of large galaxies like the Milky Way. Astronomers think that dwarf galaxy black holes could serve as an analog for black holes in the early universe, when they were just beginning to form and grow.

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Astronomers make most distant detection yet of fluorine in star-forming galaxy

A new discovery is shedding light on how fluorine -- an element found in our bones and teeth as fluoride -- is forged in the Universe. Using the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, a team of astronomers have detected this element in a galaxy that is so far away its light has taken over 12 billion years to reach us. This is the first time fluorine has been spotted in such a distant star-forming galaxy.

"We all know about fluorine because the toothpaste we use every day contains it in the form of fluoride," says Maximilien Franco from the University of Hertfordshire in the UK, who led the new study, published today in Nature Astronomy. Like most elements around us, fluorine is created inside stars but, until now, we did not know exactly how this element was produced. "We did not even know which type of stars produced the majority of fluorine in the Universe!"

Franco and his collaborators spotted fluorine (in the form of hydrogen fluoride) in the large clouds of gas of the distant galaxy NGP-190387, which we see as it was when the Universe was only 1.4 billion years old, about 10% of its current age. Since stars expel the elements they form in their cores as they reach the end of their lives, this detection implies that the stars that created fluorine must have lived and died quickly.

The team believes that Wolf-Rayet stars, very massive stars that live only a few million years, a blink of the eye in the Universe's history, are the most likely production sites of fluorine. They are needed to explain the amounts of hydrogen fluoride the team spotted, they say. Wolf-Rayet stars had been suggested as possible sources of cosmic fluorine before, but astronomers did not know until now how important they were in producing this element in the early Universe.

"We have shown that Wolf-Rayet stars, which are among the most massive stars known and can explode violently as they reach the end of their lives, help us, in a way, to maintain good dental health!" jokes Franco.

Besides these stars, other scenarios for how fluorine is produced and expelled have been put forward in the past. An example includes pulsations of giant, evolved stars with masses up to few times that of our Sun, called asymptotic giant branch stars. But the team believes these scenarios, some of which take billions of years to occur, might not fully explain the amount of fluorine in NGP-190387.

"For this galaxy, it took just tens or hundreds of millions of years to have fluorine levels comparable to those found in stars in the Milky Way, which is 13.5 billion years old. This was a totally unexpected result," says Chiaki Kobayashi, a professor at the University of Hertfordshire. "Our measurement adds a completely new constraint on the origin of fluorine, which has been studied for two decades."

The discovery in NGP-190387 marks one of the first detections of fluorine beyond the Milky Way and its neighbouring galaxies. Astronomers have previously spotted this element in distant quasars, bright objects powered by supermassive black holes at the centre of some galaxies. But never before had this element been observed in a star-forming galaxy so early in the history of the Universe.

The team's detection of fluorine was a chance discovery made possible thanks to the use of space and ground-based observatories. NGP-190387, originally discovered with the European Space Agency's Herschel Space Observatory and later observed with the Chile-based ALMA, is extraordinarily bright for its distance. The ALMA data confirmed that the exceptional luminosity of NGP-190387 was partly caused by another known massive galaxy, located between NGP-190387 and the Earth, very close to the line of sight. This massive galaxy amplified the light observed by Franco and his collaborators, enabling them to spot the faint radiation emitted billions of years ago by the fluorine in NGP-190387.

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ALMA animation of circling twin young stars

Researchers analyzed the accumulated data from the Atacama Large Millimeter/submillimeter Array (ALMA) and depicted the motion of a young twin star system XZ Tauri over three years. This first-ever "ALMA Animation" of twin stars sheds new light on the origins of the binary stars and the planets to be formed around them.

"This achievement was made possible by the high resolution and rich archival data of ALMA," says Takanori Ichikawa, the first author of the research paper and a former graduate student at Kagoshima University, Japan. "This research utilized three years of observation data. The results show the feasibility of a new research method using radio astronomical animations instead of conventional images. I hope that this method will help to clarify various astronomical phenomena in the future."

The Sun is a single star, but the Universe is full of binary stars, which are two stars orbiting each other. During its youth, each young star in a binary system is surrounded by a protoplanetary disk composed of molecular gas and dust. This disk is known to be the site of planet formation. Many planets associated with binary stars have actually been detected, but how the disks are formed in binary star systems and how planets are formed in those systems is still a mystery.

"In order to study the formation of planets in binary star systems, it is important to accurately determine the orbital motion of the two stars and the tilt of the individual protoplanetary disks," explains Shigehisa Takakuwa, a professor at Kagoshima University.

Researchers have suggested two formation mechanisms for binary systems; one is a breakup of a single large gaseous disk, and the other is fragmentation of the larger molecular cloud due to violent turbulence. In the former case, astronomers suppose that the orbit of the binary stars and the individual disks should be on the same plane. On the other hand, in the latter case, the orbital plane of the binary stars and the plane of the disks are expected to be different. This is a major issue that will affect the final orbits of the planets in binary systems.

The research team dug into the ALMA data archive and obtained the data for the young XZ Tau system taken in 2015, 2016, and 2017. They carefully analyzed the data and for the first time made an animation of the orbital motion of the binary stars, which shows that XZ Tau B moved 3.4 astronomical units (3.4 times the radius of Earth's orbit) around XZ Tau A during these three years.

The team figured out the three-dimensional structure of the orbit. In addition, analyzing the doppler effect and the distribution of the radio waves from the disk around each star in the XZ Tau system, they found that those disks are significantly misaligned with respect to each other, and also not in the same plane as the binary orbit.

Previous observations with ALMA had found examples of young binary stars with protoplanetary disks tilted with respect to each other (Note). However, this is the first time that the orbital motion of a binary system has been clarified, showing that the inclination is different from those of the circumstellar disks. These results support the idea that the XZ Tau system was formed via molecular cloud fragmentation.

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Astrophysicists solve 'empty sky' gamma-ray mystery

Star-forming galaxies are responsible for creating gamma-rays that until now had not been associated with a known origin, researchers from The Australian National University (ANU) have confirmed.

Lead author Dr Matt Roth, from the ANU Research School of Astronomy and Astrophysics, said until now it has been unclear what created gamma-rays -- one of the most energetic forms of light in the Universe -- that appear in patches of seemingly 'empty sky'.

The discovery could offer clues to help astronomers solve other mysteries of the Universe, such as what kind of particles make up Dark Matter -- one of the holy grails of astrophysics.

"It's a significant milestone to finally discover the origins of this gamma-ray emission, solving a mystery of the Universe astronomers have been trying to decipher since the 1960s," Dr Roth said.

"There are two obvious sources that produce large amounts of gamma-rays seen in the Universe. One when gas falls into the supermassive black holes which are found at the centres of all galaxies -- called an active galactic nucleus (AGN) -- and the other associated with star formation in the disks of galaxies.

"We modelled the gamma-ray emission from all the galaxies in the Universe and compared our results with the predictions for other sources and found that it is star-forming galaxies that produce the majority of this diffuse gamma-ray radiation and not the AGN process."

ANU researchers were able to pinpoint what created these mysterious gamma-rays after obtaining a better understanding of how cosmic rays -- particles that travel at speeds very close to the speed of light -- move through the gas between the stars. Cosmic rays are important because they create large amounts of gamma-ray emission in star-forming galaxies when they collide with the interstellar gas.

Data from NASA's Hubble Space Telescope and Fermi Gamma-Ray Space Telescope was a key resource used to uncover the unknown origins of the gamma-rays. Researchers analysed information about many galaxies such as their star-formation rates, total masses, physical size and distances from Earth.

"Our model can also be used to make predictions for radio emission -- the electromagnetic radiation that has a frequency similar to a car radio -- from star-forming galaxies, which could help researchers understand more about the internal structure of galaxies," Dr Roth said.

"We are currently looking at producing maps of the gamma-ray sky that can be used to inform upcoming gamma-ray observations from next-generation telescopes. This includes the Cherenkov Telescope Array, which Australia is involved in.

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