Brightest and fastest-growing: Astronomers identify record-breaking quasar

Using the European Southern Observatory's (ESO) Very Large Telescope (VLT), astronomers have characterised a bright quasar, finding it to be not only the brightest of its kind, but also the most luminous object ever observed. Quasars are the bright cores of distant galaxies and they are powered by supermassive black holes. The black hole in this record-breaking quasar is growing in mass by the equivalent of one Sun per day, making it the fastest-growing black hole to date.

The black holes powering quasars collect matter from their surroundings in a process so energetic that it emits vast amounts of light.

So much so that quasars are some of the brightest objects in our sky, meaning even distant ones are visible from Earth.

As a general rule, the most luminous quasars indicate the fastest-growing supermassive black holes.

"We have discovered the fastest-growing black hole known to date. It has a mass of 17 billion Suns, and eats just over a Sun per day. This makes it the most luminous object in the known Universe," says Christian Wolf, an astronomer at the Australian National University (ANU) and lead author of the study published today in Nature Astronomy. The quasar, called J0529-4351, is so far away from Earth that its light took over 12 billion years to reach us.

The matter being pulled in toward this black hole, in the form of a disc, emits so much energy that J0529-4351 is over 500 trillion times more luminous than the Sun.

"All this light comes from a hot accretion disc that measures seven light-years in diameter -- this must be the largest accretion disc in the Universe," says ANU PhD student and co-author Samuel Lai.

Seven light-years is about 15,000 times the distance from the Sun to the orbit of Neptune.

And, remarkably, this record-breaking quasar was hiding in plain sight.

"It is a surprise that it has remained unknown until today, when we already know about a million less impressive quasars. It has literally been staring us in the face until now," says co-author Christopher Onken, an astronomer at ANU.

He added that this object showed up in images from the ESO Schmidt Southern Sky Survey dating back to 1980, but it was not recognised as a quasar until decades later.

Finding quasars requires precise observational data from large areas of the sky.

The resulting datasets are so large, researchers often use machine-learning models to analyse them and tell quasars apart from other celestial objects.

However, these models are trained on existing data, which limits the potential candidates to objects similar to those already known.

If a new quasar is more luminous than any other previously observed, the programme might reject it and classify it instead as a star not too distant from Earth.

An automated analysis of data from the European Space Agency's Gaia satellite passed over J0529-4351 for being too bright to be a quasar, suggesting it to be a star instead.

The researchers identified it as a distant quasar last year using observations from the ANU 2.3-metre telescope at the Siding Spring Observatory in Australia.

Discovering that it was the most luminous quasar ever observed, however, required a larger telescope and measurements from a more precise instrument.

The X-shooter spectrograph on ESO's VLT in the Chilean Atacama Desert provided the crucial data.

The fastest-growing black hole ever observed will also be a perfect target for the GRAVITY+ upgrade on ESO's VLT Interferometer (VLTI), which is designed to accurately measure the mass of black holes, including those far away from Earth.

Additionally, ESO's Extremely Large Telescope (ELT), a 39-metre telescope under construction in the Chilean Atacama Desert, will make identifying and characterising such elusive objects even more feasible.

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Gas on the run -- ALMA spots the shadow of a molecular outflow from a quasar when the Universe was less than one billion years old

Theoretical predictions have been confirmed with the discovery of an outflow of molecular gas from a quasar when the Universe was less than a billion years old.

A quasar is a compact region powered by a supermassive black hole located in the center of a massive galaxy.

They are extremely luminous, with a point-like appearance similar to stars, and are extremely distant from Earth.

Owing to their distance and brightness, they provide a peek into conditions of the early Universe, when it was less than 1 billion years old.

A team of researchers led by Assistant Professor Dragan Salak at Hokkaido University, Assistant Professor Takuya Hashimoto at the University of Tsukuba, and Professor Akio Inoue at Waseda University, has discovered the first evidence of suppression of star formation driven by an outflow of molecular gas in a quasar-host galaxy in the early Universe.

Their findings, based on observations they made using the Atacama Large Millimeter/submillimeter Array (ALMA), in Chile, were published in The Astrophysical Journal.

Molecular gas is vital to the formation of stars. As the primary fuel of star formation, the ubiquity and high concentrations of molecular gas within a galaxy would lead to a vast number of stars being formed.

By ejecting this gas into intergalactic space faster than it could be consumed by star formation, molecular outflows effectively suppress the formation of stars in galaxies that host quasars.

"Theoretical work suggests that molecular gas outflows play an important role in the formation and evolution of galaxies from an early age, because they can regulate star formation," Salak explains.

"Quasars are especially energetic sources, so we expected that they may be able to generate powerful outflows."

The quasar the researchers observed, J2054-0005, has a very high redshift -- it and the Earth are apparently moving away from each other very fast.

"J2054-0005 is one of the brightest quasars in the distant Universe, so we decided to target this object as an excellent candidate to study powerful outflows," Hashimoto says.

The researchers used ALMA to observe the outflow of molecular gas from the quasar.

As the only telescope in the world that has the sensitivity and frequency coverage to detect molecular gas outflows in the early Universe, ALMA was key to this study.

Speaking about the method used in the study, Salak comments: "The outflowing molecular (OH) gas was discovered in absorption. This means we did not observe microwave radiation coming directly from the OH molecules; instead, we observed the radiation coming from the bright quasar -- and absorption means that OH molecules happened to absorb a part of the radiation from the quasar. So, it was like revealing the presence of a gas by seeing the 'shadow' it cast in front of the light source."

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Dark matter halos measured around ancient quasars

At the center of every galaxy is a supermassive black hole. Beyond a certain size, these become active, emitting huge amounts of radiation, and are then called quasars. It is thought these are activated by the presence of massive dark matter halos (DMH) surrounding the galaxy, directing matter towards the center, feeding the black hole. A team including researchers from the University of Tokyo have, for the first time, surveyed hundreds of ancient quasars and found this behavior is very consistent throughout history. This is surprising, as many large-scale processes show variation throughout the life of the universe, so the mechanism of quasar activation could have implications for the evolution of the entire universe.

Measuring the mass of DMHs is not easy; it's famously a very elusive substance, if substance is even the right word to use, given the actual nature of dark matter is unknown. We only know it exists at all due to its gravitational impact on large structures such as galaxies. Thus, dark matter can only be measured by making observations about its gravitational effects on things. This includes the way it might pull on something or affect its movement, or through the lensing (bending of light) of objects behind a suspected area of dark matter.

The challenge becomes greater at large distances, given how weak the light from more distant, and therefore ancient, phenomena can be. But this did not stop Professor Nobunari Kashikawa from the Department of Astronomy, and his team, from trying to answer a long-standing question in astronomy: How are black holes born, and how do they grow? The researchers are especially keen to explore this in relation to supermassive black holes, the largest kind, which exist in the heart of every galaxy. These would be very difficult to study were it not for the fact that some grow so massive they begin to output incredibly powerful jets of matter or spheres of radiation that in either case become what we call quasars. These are so powerful that even at large distances, we can now observe them using modern techniques.

"We measured for the first time the typical mass for dark matter halos surrounding an active black hole in the universe about 13 billion years ago," said Kashikawa. "We find the DMH mass of quasars is pretty constant at about 10 trillion times the mass of our sun. Such measurements have been made for more recent DMH around quasars, and those measurements are strikingly similar to what we see for more ancient quasars. This is interesting because it suggests there is a characteristic DMH mass which seems to activate a quasar, regardless of whether it happened billions of years ago or right now."

Quasars at great distances appear faint, as the light which left them long ago has spread out, was absorbed by intervening matter, and has been stretched into nearly invisible infrared wavelengths due to the universe expanding over time. So Kashikawa and his team, whose project began in 2016, used multiple surveys of the sky which incorporated a range of different instruments, the main one being Japan's Subaru Telescope, located in U.S. state of Hawaii.

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VERA unveils surroundings of rapidly growing black holes

An international team of astronomers used the state-of-the-art capability of VERA, a Japanese network of radio telescopes operated by NAOJ, to uncover valuable clues about how rapidly growing "young" supermassive black holes form, grow, and possibly evolve into more powerful quasars.

It is now widely accepted that nearly every active galaxy harbors a supermassive black hole at its core, with masses ranging from millions to billions of times that of the Sun. The growth history by which these black holes have gained such huge masses, however, remains an open question.

Led by Mieko Takamura, a graduate student at the University of Tokyo, an international team focused on a distinct category of active galaxies known as Narrow-line Seyfert 1 (NLS1) galaxies. These galaxies are suspected to contain relatively small yet rapidly growing massive black holes, thus offering a potential opportunity to study an early evolutionary stage of these cosmic monsters. To gain a deeper understanding of the immediate surroundings of these peculiar black holes, the team observed the cores of six nearby active NLS1 galaxies using VERA -- a radio telescope network with an eyesight over 100,000 times more powerful than the human eye. In particular, the team leveraged the newly enhanced ultra-wideband recording capability of VERA, enabling them to detect faint "polarized" radio waves emanating from the core of these galaxies with unprecedented precision.

A portion of radio waves emitted near supermassive black holes is known to exhibit polarization. As this polarized emission propagates through the magnetized gas surrounding the black hole, the plane of polarization gradually rotates, causing an effect known as Faraday rotation. The extent of this rotation (at a given wavelength) is proportional to the gas density and the strength of the magnetic field within the propagating medium. Therefore, polarization and Faraday rotation provide valuable insights into the immediate environment surrounding a central black hole.

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Starlight and the first black holes: researchers detect the host galaxies of quasars in the early universe

New images from the James Webb Space Telescope have revealed, for the first time, starlight from two massive galaxies hosting actively growing black holes -- quasars -- seen less than a billion years after the Big Bang. A new study in Nature this week finds the black holes have masses close to a billion times that of the Sun, and the host galaxy masses are almost one hundred times larger, a ratio similar to what is found in the more recent universe. A powerful combination of the Subaru Telescope and the JWST has paved a new path to study the distant universe.

The existence of such massive black holes in the distant universe has created more questions than answers for astrophysicists. How could these black holes grow to be so large when the universe was so young? Even more puzzling, observations in the local universe show a clear relation between the mass of supermassive black holes and the much larger galaxies in which they reside. The galaxies and the black holes have completely different sizes, so which came first: the black holes or the galaxies? This is a "chicken-or-egg" problem on a cosmic scale.

An international team of researchers, led by Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Project Researcher Xuheng Ding and Professor John Silverman, and Peking University Kavli Institute for Astronomy and Astrophysics (PKU-KIAA) Kavli Astrophysics Fellow Masafusa Onoue have started to answer this question with the James Webb Space Telescope (JWST), launched in December 2021. Studying the relation between host galaxies and black holes in the early universe allows scientists to watch their formation, and see how they are related to one another.

Quasars are luminous, while their host galaxies are faint, which has made it challenging for researchers to detect the dim light of the galaxy in the glare of the quasar, especially at great distances. Before the JWST, the Hubble Space Telescope was able to detect host galaxies of luminous quasars when the universe was just under 3 billion years old, but no younger.

The superb sensitivity and the ultra-sharp images of the JWST at infrared wavelengths finally allowed researchers to push these studies to the time when the quasars and galaxies first formed. Just a few months after JWST started regular operations, the team observed two quasars, HSC J2236+0032 and HSC J2255+0251, at redshifts 6.40 and 6.34 when the universe was approximately 860 million years old. These two quasars were discovered in a deep survey program of the 8.2m-Subaru Telescope on the summit of Maunakea in Hawai'i. The relatively low luminosities of these quasars made them prime targets for measurement of the host galaxy properties, and the successful detection of the hosts represents the earliest epoch to date at which starlight has been detected in a quasar.

The images of the two quasars were taken at infrared wavelengths of 3.56 and 1.50 micron with JWST's NIRCam instrument, and the host galaxies became apparent after carefully modeling and subtracting glare from the accreting black holes. The stellar signature of the host galaxy was also seen in a spectrum taken by JWST's NIRSPEC for J2236+0032, further supporting the detection of the host galaxy.

Analyses of the host galaxy photometry found that these two quasar host galaxies are massive, measuring 130 and 34 billion times the mass of the Sun, respectively. Measuring the speed of the turbulent gas in the vicinity of the quasars from the NIRSPEC spectra suggests that the black holes that power them are also massive, measuring 1.4 and 0.2 billion times the mass of the Sun. The ratio of the black hole mass to host galaxy mass is similar to those of galaxies in the more recent past, suggesting that the relationship between black holes and their hosts was already in place 860 million years after the Big Bang.

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DESI early data release holds nearly two million objects

The universe is big, and it's getting bigger. To study dark energy, the mysterious force behind the accelerating expansion of our universe, scientists are using the Dark Energy Spectroscopic Instrument (DESI) to map more than 40 million galaxies, quasars, and stars. Today, the collaboration publicly released its first batch of data, with nearly 2 million objects for researchers to explore.

The 80-terabyte data set comes from 2,480 exposures taken over six months during the experiment's "survey validation" phase in 2020 and 2021. In this period between turning the instrument on and beginning the official science run, researchers made sure their plan for using the telescope would meet their science goals -- for example, by checking how long it took to observe galaxies of different brightness, and by validating the selection of stars and galaxies to observe.

"The fact that DESI works so well, and that the amount of science-grade data it took during survey validation is comparable to previous completed sky surveys, is a monumental achievement," said Nathalie Palanque-Delabrouille, co-spokesperson for DESI and a scientist at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), which manages the experiment. "This milestone shows that DESI is a unique spectroscopic factory whose data will not only allow the study of dark energy but will also be coveted by the whole scientific community to address other topics, such as dark matter, gravitational lensing, and galactic morphology."

Today the collaboration also published a set of papers related to the early data release, which include early measurements of galaxy clustering, studies of rare objects, and descriptions of the instrument and survey operations. The new papers build on DESI's first measurement of the cosmological distance scale that was published in April, which used the first two months of routine survey data (not included in the early data release) and also showed DESI's ability to accomplish its design goals.

DESI uses 5,000 robotic positioners to move optical fibers that capture light from objects millions or billions of light-years away. It is the most powerful multi-object survey spectrograph in the world, able to measure light from more than 100,000 galaxies in one night. That light tells researchers how far away an object is, building a 3D cosmic map.

"Survey validation was very important for DESI because it allowed us -- before starting the main survey -- to adjust our selection of all the objects, including stars, bright galaxies, luminous red galaxies, emission line galaxies, and quasars," said Christophe Yeche, a scientist with the French Alternative Energies and Atomic Energy Commission (CEA) who co-leads the target selection group. "We've been able to optimize our selection and confirm our observation strategy."

As the universe expands, it stretches light's wavelength, making it redder -- a characteristic known as redshift. The further away the galaxy, the bigger the redshift. DESI specializes in collecting redshifts that can then be used to solve some of astrophysics' biggest puzzles: what dark energy is and how it has changed throughout the universe's history.

While DESI's primary goal is understanding dark energy, much of the data can also be used in other astronomical studies. For example, the early data release contains detailed images from some well-known areas of the sky, such as the Hubble Deep Field.

"There are some well-trodden spots where we've drilled down into the sky," said Stephen Bailey, a scientist at Berkeley Lab who leads data management for DESI. "We've taken valuable spectroscopic images in areas that are of interest to the rest of the community, and we're hoping that other people will take this data and do additional science with it."

Two interesting finds have already surfaced: Evidence of a mass migration of stars into the Andromeda galaxy, and incredibly distant quasars, the extremely bright and active supermassive black holes sometimes found at the center of galaxies.

"We observed some areas at very high depth. People have looked at that data and discovered very high redshift quasars, which are still so rare that basically any discovery of them is useful," said Anthony Kremin, a postdoctoral researcher at Berkeley Lab who led the data processing for the early data release. "Those high-redshift quasars are usually found with very large telescopes, so the fact that DESI -- a smaller, 4-meter survey instrument -- could compete with those larger, dedicated observatories was an achievement we are pretty proud of and demonstrates the exceptional throughput of the instrument."

Survey validation was also a chance to test the process of transforming raw data from DESI's ten spectrometers (which split a galaxy's light into different colors) into useful information.

"If you looked at them, the images coming directly from the camera would look like nonsense -- like lines on a weird, fuzzy image," said Laurie Stephey, a data architect at the National Energy Research Scientific Computing Center (NERSC), the supercomputer that processes DESI's data. "The magic happens in the processing and the software being able to decode the data. It's exciting that we have the technology to make that data accessible to the research community and that we can support this big question of 'what is dark energy?'"

DESI's early data was a unique project for NERSC. All of the experiment's code, including the computational heavy lifting, is written in the programming language Python rather than the traditional C++ or Fortran.

"That was the first time that using pure Python was shown to be a feasible approach for a major experiment at NERSC, and since then, Python has become increasingly common in our user workload," Stephey said.

The DESI early data release is now available to access for free through NERSC.

There is plenty of data yet to come from the experiment. DESI is currently two years into its five-year run and ahead of schedule on its quest to collect more than 40 million redshifts. The survey has already catalogued more than 26 million astronomical objects in its science run, and is adding more than a million per month.

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An X-ray look at the heart of powerful quasars

Researchers have observed the X-ray emission of the most luminous quasar seen in the last 9 billion years of cosmic history, known as SMSS J114447.77-430859.3, or J1144 for short. The new perspective sheds light on the inner workings of quasars and how they interact with their environment. The research is published in Monthly Notices of the Royal Astronomical Society.

Hosted by a galaxy 9.6 billion light years away from the Earth, between the constellations of Centaurus and Hydra, J1144 is extremely powerful, shining 100,000 billion times brighter than the Sun. J1144 is much closer to Earth than other sources of the same luminosity, allowing astronomers to gain insight into the black hole powering the quasar and its surrounding environment. The study was led by Dr Elias Kammoun, a postdoctoral researcher at the Research Institute in Astrophysics and Planetology (IRAP), and Zsofi Igo, a PhD candidate at the Max Planck Institute for Extraterrestrial Physics (MPE).

Quasars are among the brightest and most distant objects in the known universe, powered by the fall of gas into a supermassive black hole. They can be described as active galactic nuclei (AGN) of very high luminosity that emit vast amounts of electromagnetic radiation observable in radio, infrared, visible, ultraviolet and X-ray wavelengths. J1144 was initially observed in visible wavelengths in 2022 by the SkyMapper Southern Survey (SMSS).

For this study, researchers combined observations from several space-based observatories: the eROSITA instrument on board the Spectrum-Roentgen-Gamma (SRG) observatory, the ESA XMM-Newton observatory, NASA's Nuclear Spectroscopic Telescope Array (NuSTAR), and NASA's Neil Gehrels Swift observatory.

The team used the data from the four observatories to measure the temperature of the X-rays being emitted from the quasar. They found this temperature to be around 350 million Kelvin, more than 60,000 times the temperature at the surface of the Sun. The team also found that the mass of the black hole at the quasar's centre is around 10 billion times the mass of the Sun, and the rate at which it is growing to be of the order of 100 solar masses per year.

The X-ray light from this source varied on a time scale of a few days, which is not usually seen in quasars with black holes as large as the one residing in J1144. The typical timescale of variability for a black hole of this size would be on the order of months or even years. The observations also showed that while a portion of the gas is swallowed by the black hole, some gas is ejected in the form of extremely powerful winds, injecting large amounts of energy into the host galaxy.

Dr. Kammoun, lead author of the paper, says "We were very surprised that no prior X-ray observatory has ever observed this source despite its extreme power."

He adds, "Similar quasars are usually found at much larger distances, so they appear much fainter, and we see them as they were when the Universe was only 2-3 billion years old. J1144 is a very rare source as it is so luminous and much closer to Earth (although still at a huge distance!), giving us a unique glimpse of what such powerful quasars look like."

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Astronomers solve the 60-year mystery of quasars -- the most powerful objects in the Universe

Scientists have unlocked one of the biggest mysteries of quasars -- the brightest, most powerful objects in the Universe -- by discovering that they are ignited by galaxies colliding.

First discovered 60 years ago, quasars can shine as brightly as a trillion stars packed into a volume the size of our Solar System. In the decades since they were first observed, it has remained a mystery what could trigger such powerful activity. New work led by scientists at the Universities of Sheffield and Hertfordshire has now revealed that it is a consequence of galaxies crashing together.

The collisions were discovered when researchers, using deep imaging observations from the Isaac Newton Telescope in La Palma, observed the presence of distorted structures in the outer regions of the galaxies that are home to quasars.

Most galaxies have supermassive black holes at their centres. They also contain substantial amounts of gas -- but most of the time this gas is orbiting at large distances from the galaxy centres, out of reach of the black holes. Collisions between galaxies drive the gas towards the black hole at the galaxy centre; just before the gas is consumed by the black hole, it releases extraordinary amounts of energy in the form of radiation, resulting in the characteristic quasar brilliance.

The ignition of a quasar can have dramatic consequences for entire galaxies -- it can drive the rest of the gas out of the galaxy, which prevents it from forming new stars for billions of years into the future.

This is the first time that a sample of quasars of this size has been imaged with this level of sensitivity. By comparing observations of 48 quasars and their host galaxies with images of over 100 non-quasar galaxies, researchers concluded that galaxies hosting quasars are approximately three times as likely to be interacting or colliding with other galaxies.

The study has provided a significant step forward in our understanding of how these powerful objects are triggered and fuelled.

Professor Clive Tadhunter, from the University of Sheffield's Department of Physics and Astronomy, said: "Quasars are one of the most extreme phenomena in the Universe, and what we see is likely to represent the future of our own Milky Way galaxy when it collides with the Andromeda galaxy in about five billion years.

"It's exciting to observe these events and finally understand why they occur -- but thankfully Earth won't be anywhere near one of these apocalyptic episodes for quite some time."

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New simulation shows how galaxies feed their supermassive black holes

Galaxies' spiral arms are responsible for scooping up gas to feed to their central supermassive black holes, according to a new high-powered simulation.

Started at Northwestern University, the simulation is the first to show, in great detail, how gas flows across the universe all the way down to the center of a supermassive black hole. While other simulations have modeled black hole growth, this is the first single computer simulation powerful enough to comprehensively account for the numerous forces and factors that play into the evolution of supermassive black holes.

The simulation also gives rare insight into the mysterious nature of quasars, which are incredibly luminous, fast-growing black holes. Some of the brightest objects in the universe, quasars often even outshine entire galaxies.

"The light we observe from distant quasars is powered as gas falls into supermassive black holes and gets heated up in the process," said Northwestern's Claude-André Faucher-Giguère, one of the study's senior authors. "Our simulations show that galaxy structures, such as spiral arms, use gravitational forces to 'put the brakes on' gas that would otherwise orbit galaxy centers forever. This breaking mechanism enables the gas to instead fall into black holes and the gravitational brakes, or torques, are strong enough to explain the quasars that we observe."

The research was published today(Aug. 17) in the Astrophysical Journal.

Faucher-Giguèreis an associate professor of physics and astronomy at Northwestern's Weinberg College of Arts and Sciencesand a member of the Center for Interdisciplinary Exploration and Research in Astrophysics(CIERA). Daniel Anglés-Alcázar, an assistant professor at the University of Connecticut and former CIERA fellow inFaucher-Giguère's group, is the paper's first author.

Equivalent to the mass of millions or even billions of suns, supermassive black holes can swallow 10 times the mass of a sun in just one year. But while some supermassive black holes enjoy a continuous supply of food, others go dormant for millions of years, only to reawaken abruptly with a serendipitous influx of gas. The details about how gas flows across the universe to feed supermassive black holes have remained a long-standing question.

To address this mystery, the research team developed the new simulation, which incorporates many of the key physical processes -- including the expansion of the universe and the galactic environment on large scales, gravity gas hydrodynamics and feedback from massive stars -- into one model.

"Powerful events such as supernovae inject a lot of energy into the surrounding medium, and this influences how the galaxy evolves," Anglés-Alcázar said. "So we need to incorporate all of these details and physical processes to capture an accurate picture."

Building on previous work from the FIRE ("Feedback In Realistic Environments") project, the new technology greatly increases model resolution and allows for following the gas as it flows across the galaxy with more than 1,000 times better resolution than previously possible.

"Other models can tell you a lot of details about what's happening very close to the black hole, but they don't contain information about what the rest of the galaxy is doing or even less about what the environment around the galaxy is doing," Anglés-Alcázar said. "It turns out, it is very important to connect all these processes at the same time."

"The very existence of supermassive black holes is quite amazing, yet there is no consensus on how they formed," Faucher-Giguère said. "The reason supermassive black holes are so difficult to explain is that forming them requires cramming a huge amount of matter into a tiny space. How does the universe manage to do that? Until now, theorists developed explanations relying on patching together different ideas for how matter in galaxies gets crammed into the innermost one millionth of a galaxy's size."

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Cracking a mystery of massive black holes and quasars with supercomputer simulations

At the center of galaxies, like our own Milky Way, lie massive black holes surrounded by spinning gas. Some shine brightly, with a continuous supply of fuel, while others go dormant for millions of years, only to reawaken with a serendipitous influx of gas. It remains largely a mystery how gas flows across the universe to feed these massive black holes.

UConn Assistant Professor of Physics Daniel Anglés-Alcázar, lead author on a paper published today in The Astrophysical Journal, addresses some of the questions surrounding these massive and enigmatic features of the universe by using new, high-powered simulations.

"Supermassive black holes play a key role in galaxy evolution and we are trying to understand how they grow at the centers of galaxies," says Anglés-Alcázar. "This is very important not just because black holes are very interesting objects on their own, as sources of gravitational waves and all sorts of interesting stuff, but also because we need to understand what the central black holes are doing if we want to understand how galaxies evolve."

Anglés-Alcázar, who is also an Associate Research Scientist at the Flatiron Institute Center for Computational Astrophysics, says a challenge in answering these questions has been creating models powerful enough to account for the numerous forces and factors that play into the process. Previous works have looked either at very large scales or the very smallest of scales, "but it has been a challenge to study the full range of scales connected simultaneously."

Galaxy formation, Anglés-Alcázar says, starts with a halo of dark matter that dominates the mass and gravitational potential in the area and begins pulling in gas from its surroundings. Stars form from the dense gas, but some of it must reach the center of the galaxy to feed the black hole. How does all that gas get there? For some black holes, this involves huge quantities of gas, the equivalent of ten times the mass of the sun or more swallowed in just one year, says Anglés-Alcázar.

"When supermassive black holes are growing very fast, we refer to them as quasars," he says. "They can have a mass well into one billion times the mass of the sun and can outshine everything else in the galaxy. How quasars look depends on how much gas they add per unit of time. How do we manage to get so much gas down to the center of the galaxy and close enough that the black hole can grab it and grow from there?"

The new simulations provide key insights into the nature of quasars, showing that strong gravitational forces from stars can twist and destabilize the gas across scales, and drive sufficient gas influx to power a luminous quasar at the epoch of peak galaxy activity.

In visualizing this series of events, it is easy to see the complexities of modeling them, and Anglés-Alcázar says it is necessary to account for the myriad components influencing black hole evolution.

"Our simulations incorporate many of the key physical processes, for example, the hydrodynamics of gas and how it evolves under the influence of pressure forces, gravity, and feedback from massive stars. Powerful events such as supernovae inject a lot of energy into the surrounding medium and this influences how the galaxy evolves, so we need to incorporate all of these details and physical processes to capture an accurate picture."

Building on previous work from the FIRE ("Feedback In Realistic Environments") project, Anglés-Alcázar explains the new technique outlined in the paper that greatly increases model resolution and allows for following the gas as it flows across the galaxy with more than a thousand times better resolution than previously possible,

"Other models can tell you a lot of details about what's happening very close to the black hole, but they don't contain information about what the rest of the galaxy is doing, or even less, what the environment around the galaxy is doing. It turns out, it is very important to connect all of these processes at the same time, this is where this new study comes in."

The computing power is similarly massive, Anglés-Alcázar says, with hundreds of central processing units (CPUs) running in parallel that could have easily taken the length of millions of CPU hours.

"This is the first time that we have been able to create a simulation that can capture the full range of scales in a single model and where we can watch how gas is flowing from very large scales all the way down to the very center of the massive galaxy that we are focusing on."

For future studies of large statistical populations of galaxies and massive black holes, we need to understand the full picture and the dominant physical mechanisms for as many different conditions as possible, says Anglés-Alcázar.

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Hubble spots double quasars in merging galaxies

 NASA's Hubble Space Telescope is "seeing double." Peering back 10 billion years into the universe's past, Hubble astronomers found a pair of quasars that are so close to each other they look like a single object in ground-based telescopic photos, but not in Hubble's crisp view.

The researchers believe the quasars are very close to each other because they reside in the cores of two merging galaxies. The team went on to win the "daily double" by finding yet another quasar pair in another colliding galaxy duo.

A quasar is a brilliant beacon of intense light from the center of a distant galaxy that can outshine the entire galaxy. It is powered by a supermassive black hole voraciously feeding on inflating matter, unleashing a torrent of radiation.

"We estimate that in the distant universe, for every 1,000 quasars, there is one double quasar. So finding these double quasars is like finding a needle in a haystack," said lead researcher Yue Shen of the University of Illinois at Urbana-Champaign.

The discovery of these four quasars offers a new way to probe collisions among galaxies and the merging of supermassive black holes in the early universe, researchers say.

Quasars are scattered all across the sky and were most abundant 10 billion years ago. There were a lot of galaxy mergers back then feeding the black holes. Therefore, astronomers theorize there should have been many dual quasars during that time.

"This truly is the first sample of dual quasars at the peak epoch of galaxy formation with which we can use to probe ideas about how supermassive black holes come together to eventually form a binary," said research team member Nadia Zakamska of Johns Hopkins University in Baltimore, Maryland.

The team's results appeared in the April 1 online issue of the journal Nature Astronomy.

Shen and Zakamska are members of a team that is using Hubble, the European Space Agency's Gaia space observatory, and the Sloan Digital Sky Survey, as well as several ground-based telescopes, to compile a robust census of quasar pairs in the early universe.

The observations are important because a quasar's role in galactic encounters plays a critical part in galaxy formation, the researchers say. As two close galaxies begin to distort each other gravitationally, their interaction funnels material into their respective black holes, igniting their quasars.

Over time, radiation from these high-intensity "light bulbs" launch powerful galactic winds, which sweep out most of the gas from the merging galaxies. Deprived of gas, star formation ceases, and the galaxies evolve into elliptical galaxies.

"Quasars make a profound impact on galaxy formation in the universe," Zakamska said. "Finding dual quasars at this early epoch is important because we can now test our long-standing ideas of how black holes and their host galaxies evolve together."

Astronomers have discovered more than 100 double quasars in merging galaxies so far. However, none of them is as old as the two double quasars in this study.

The Hubble images show that quasars within each pair are only about 10,000 light-years apart. By comparison, our Sun is 26,000 light-years from the supermassive black hole in the center of our galaxy.

The pairs of host galaxies will eventually merge, and then the quasars also will coalesce, resulting in an even more massive, single solitary black hole.

Finding them wasn't easy. Hubble is the only telescope with vision sharp enough to peer back to the early universe and distinguish two close quasars that are so far away from Earth. However, Hubble's sharp resolution alone isn't good enough to find these dual light beacons.

Astronomers first needed to figure out where to point Hubble to study them. The challenge is that the sky is blanketed with a tapestry of ancient quasars that flared to life 10 billion years ago, only a tiny fraction of which are dual. It took an imaginative and innovative technique that required the help of the European Space Agency's Gaia satellite and the ground-based Sloan Digital Sky Survey to compile a group of potential candidates for Hubble to observe.

Located at Apache Point Observatory in New Mexico, the Sloan telescope produces three-dimensional maps of objects throughout the sky. The team pored through the Sloan survey to identify the quasars to study more closely.

The researchers then enlisted the Gaia observatory to help pinpoint potential double-quasar candidates. Gaia measures the positions, distances, and motions of nearby celestial objects very precisely. But the team devised a new, innovative application for Gaia that could be used for exploring the distant universe. They used the observatory's database to search for quasars that mimic the apparent motion of nearby stars. The quasars appear as single objects in the Gaia data. However, Gaia can pick up a subtle, unexpected "jiggle" in the apparent position of some of the quasars it observes.

The quasars aren't moving through space in any measurable way, but instead their jiggle could be evidence of random fluctuations of light as each member of the quasar pair varies in brightness. Quasars flicker in brightness on timescales of days to months, depending on their black hole's feeding schedule.

This alternating brightness between the quasar pair is similar to seeing a railroad crossing signal from a distance. As the lights on both sides of the stationary signal alternately flash, the sign gives the illusion of "jiggling."

When the first four targets were observed with Hubble, its crisp vision revealed that two of the targets are two close pairs of quasars. The researchers said it was a "light bulb moment" that verified their plan of using Sloan, Gaia, and Hubble to hunt for the ancient, elusive double powerhouses.

Team member Xin Liu of the University of Illinois at Urbana-Champaign called the Hubble confirmation a "happy surprise." She has long hunted for double quasars closer to Earth using different techniques with ground-based telescopes. "The new technique can not only discover dual quasars much further away, but it is much more efficient than the methods we've used before," she said.

Their Nature Astronomy article is a "proof of concept that really demonstrates that our targeted search for dual quasars is very efficient," said team member Hsiang-Chih Hwang, a graduate student at Johns Hopkins University and the principal investigator of the Hubble program. "It opens a new direction where we can accumulate a lot more interesting systems to follow up, which astronomers weren't able to do with previous techniques or datasets."

The team also obtained follow-up observations with the National Science Foundation NOIRLab's Gemini telescopes. "Gemini's spatially-resolved spectroscopy can unambiguously reject interlopers due to chance superpositions from unassociated star-quasar systems, where the foreground star is coincidentally aligned with the background quasar," said team member Yu-Ching Chen, a graduate student at the University of Illinois at Urbana-Champaign.

Although the team is convinced of their result, they say there is a slight chance that the Hubble snapshots captured double images of the same quasar, an illusion caused by gravitational lensing. This phenomenon occurs when the gravity of a massive foreground galaxy splits and amplifies the light from the background quasar into two mirror images. However, the researchers think this scenario is highly unlikely because Hubble did not detect any foreground galaxies near the two quasar pairs.

Galactic mergers were more plentiful billions of years ago, but a few are still happening today. One example is NGC 6240, a nearby system of merging galaxies that has two and possibly even three supermassive black holes. An even closer galactic merger will occur in a few billion years when our Milky Way galaxy collides with neighboring Andromeda galaxy. The galactic tussle would likely feed the supermassive black holes in the core of each galaxy, igniting them as quasars.

Future telescopes may offer more insight into these merging systems. NASA's James Webb Space Telescope, an infrared observatory scheduled to launch later this year, will probe the quasars' host galaxies. Webb will show the signatures of galactic mergers, such as the distribution of starlight and the long streamers of gas pulled from the interacting galaxies.

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Quasar discovery sets new distance record

 An international team of astronomers has discovered the most distant quasar yet found -- a cosmic monster more than 13 billion light-years from Earth powered by a supermassive black hole more than 1.6 billion times more massive than the Sun and more than 1,000 times brighter than our entire Milky Way Galaxy.

The quasar, called J0313-1806, is seen as it was when the Universe was only 670 million years old and is providing astronomers with valuable insight on how massive galaxies -- and the supermassive black holes at their cores -- formed in the early Universe. The scientists presented their findings to the American Astronomical Society's meeting, now underway virtually, and in a paper accepted to the Astrophysical Journal Letters.

The new discovery beats the previous distance record for a quasar set three years ago. Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile confirmed the distance measurement to high precision.

Quasars occur when the powerful gravity of a supermassive black hole at a galaxy's core draws in surrounding material that forms an orbiting disk of superheated material around the black hole. The process releases tremendous amounts of energy, making the quasar extremely bright, often outshining the rest of the galaxy.

The black hole at the core of J0313-1806 is twice as massive as that of the previous record holder and that fact provides astronomers with a valuable clue about such black holes and their affect on their host galaxies.

"This is the earliest evidence of how a supermassive black hole is affecting the galaxy around it," said Feige Wang, a Hubble Fellow at the University of Arizona's Steward Observatory and leader of the research team. "From observations of less distant galaxies, we know that this has to happen, but we have never seen it happening so early in the Universe."

The huge mass of J0313-1806's black hole at such an early time in the Universe's history rules out two theoretical models for how such objects formed, the astronomers said. In the first of these models, individual massive stars explode as supernovae and collapse into black holes that then coalesce into larger black holes. In the second, dense clusters of stars collapse into a massive black hole. In both cases, however, the process takes too long to produce a black hole as massive as the one in J0313-1806 by the age at which we see it.

"This tells you that no matter what you do, the seed of this black hole must have formed by a different mechanism," said Xiaohui Fan, also of the University of Arizona. "In this case, it's a mechanism that involves vast quantities of primordial, cold hydrogen gas directly collapsing into a seed black hole."

The ALMA observations of J0313-1806 provided tantalizing details about the quasar host galaxy, which is forming new stars at a rate 200 times that of our Milky Way. "This is a relatively high star formation rate in galaxies of similar age, and it indicates that the quasar host galaxy is growing very fast," said Jinyi Yang, the second author of the report, who is a Peter A. Strittmatter Fellow at the University of Arizona.

The quasar's brightness indicates that the black hole is swallowing the equivalent of 25 Suns every year. The energy released by that rapid feeding, the astronomers said, probably is powering a powerful outflow of ionized gas seen moving at about 20 percent of the speed of light.

Such outflows are thought to be what ultimately stops star formation in the galaxy.

"We think those supermassive black holes were the reason why many of the big galaxies stopped forming stars at some point," Fan said. "We observe this 'quenching' at later times, but until now, we didn't know how early this process began in the history of the Universe. This quasar is the earliest evidence that quenching may have been happening at very early times."

This process also will leave the black hole with nothing left to eat and halt its growth, Fan pointed out.

In addition to ALMA, the astronomers used the 6.5-meter Magellan Baade telescope, the Gemini North telescope and W.M. Keck Observatory in Hawaii, and the Gemini South telescope in Chile.

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Puzzling 'cold quasar' forming new stars in spite of active galactic nucleus

 Researchers from the University of Kansas have described a galaxy more than 5.25 billion light years away undergoing a rarely seen stage in its galactic life cycle. Their findings recently were published in the Astrophysical Journal.

The galaxy, dubbed CQ 4479, shows characteristics that normally don't coexist: an X-ray luminous active galactic nuclei (AGN) and a cold gas supply fueling high star formation rates.

"Massive galaxies, such as our own Milky Way, host a supermassive black hole at their hearts -- these are black holes that grow by accreting interstellar gas onto themselves to become more massive," said Kevin Cooke, lead author and postdoctoral researcher in KU's Department of Physics & Astronomy. "The end of galactic growth is thought to happen when this gas accretion onto the black hole occurs in sufficient quantities that it produces a tremendous amount of energy. Then, all of that energy surrounding the black hole will actually heat up the rest of the gas throughout the galaxy in such a way that it can't condense any more to form stars and the galaxy's growth stops."

The KU researchers instead found CQ 4479, a galaxy which never had been closely studied before, to be still generating new stars in spite of the luminous AGN at the galaxy's center.

"Normally, we expect that to shut everything else off," Cooke said. "But instead, we see massive amounts of new stars being formed in this galaxy. So, it's a very limited time window where you can see both the black hole growing and the stars surrounding it growing at the same time."

The researchers observed the cold quasar primarily using NASA's SOFIA infrared telescope, which is flown aboard a Boeing 747 aircraft. Other measurements were made using FUV-FIR photometry and optical spectroscopy. The work was supported by a NASA grant to primary investigator Allison Kirkpatrick, assistant professor of physics & astronomy at KU, who co-wrote the new paper.

Kirkpatrick said the team's various methods of observing the galaxy showed contradictory data, making the nature of CQ 4479 even more of a puzzle.

"What's really unique about this source is we have different measurements of the energy output near the black hole," Kirkpatrick said. "That tells you how fast the black hole is growing and also its feedback into the host galaxy that can shut down star formation. We have everything from X-ray, to optical and the infrared, so we're able to measure several different signatures of the black hole's energy output. And the signatures don't agree -- that's really rare. One interpretation is the growth of the black hole is slowing, because the X-rays come from right next to the black hole, while the optical signatures come from a little bit further out, and the infrared signatures come from further out as well. Essentially, less energy seems to be being produced right around the black hole now than it was in the past."

The researchers seem to be looking at a snapshot of the galaxy during a pivotal stage of its lifespan.

"I think this is a galaxy undergoing a midlife crisis," Kirkpatrick said. "It's going through one last burst of star formation. Most of its solar mass is already in place. It's forming a few more stars now, and the thing that's ultimately going to kill it is starting to kick in."

In part, the research at KU was performed by Kirkpatrick's undergraduate student and co-author Michael Estrada, now a graduate student at University of Florida.

"He did the data analysis of the optical spectroscopy and measured the black hole mass for us," Kirkpatrick said.

Other questions about the physical structure of the galaxy remain because current instrumentation available to astronomers don't provide clear enough images of CQ 4479.

"The image we have shows a central blob and then a little smaller blob below it," Kirkpatrick said. "So we don't have a good sense for how this galaxy looks because the central AGN is so bright that it out shines the rest of the host galaxy. This is a real problem that plagues all AGN studies -- when you're dealing with the most luminous things they tend to outshine your host at nearly every wavelength."

The researchers said CQ 4479 would require more study, particularly using the ALMA Observatory and the NASA's James Webb Space Telescope -- the most powerful space telescope ever designed and currently slated for launch Oct. 31, 2021. Both Cooke and Kirkpatrick hope to perform more investigations of the strange cold quasar once the telescope is launched.

"We're currently banking on James Webb, because it will have excellent resolution and we should be able to look at wavelengths where we can see the shape of the galaxy," Kirkpatrick said. "Another good option would be ALMA. But ALMA has unfortunately shut down temporarily because of COVID. We've kind of been stymied at seeing the host galaxy."

The importance of understanding the strange processes underway in a galaxy 5.25 billion light years from Earth might seem vague at first, but Cooke said a better understanding of the cold quasar could improve understanding of the cosmos and the fate of our own galaxy.

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Rare encounters between cosmic heavyweights

 A cosmic dance between two merging galaxies, each one containing a supermassive black hole that's rapidly feeding on so much material it creates a phenomenon known as a quasar, is a rare find.

Astronomers have discovered several pairs of such merging galaxies, or luminous "dual" quasars, using three Maunakea Observatories in Hawaii -- Subaru Telescope, W. M. Keck Observatory, and Gemini Observatory.

These dual quasars are so rare, a research team led by the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo estimates only 0.3% of all known quasars have two supermassive black holes that are on a collision course with each other.

The study is published in the August 26, 2020 issue of the Astrophysical Journal.

"In spite of their rarity, they represent an important stage in the evolution of galaxies, where the central giant is awakened, gaining mass, and potentially impacting the growth of its host galaxy," said Shenli Tang, a graduate student at the University of Tokyo and co-author of the study.

Quasars are one of the most luminous, energetic objects known in the universe, powered by supermassive black holes that are millions to billions times more massive than our Sun. As material swirls around a black hole at the center of a galaxy, it is heated to high temperatures, releasing so much light that the quasar can outshine its host galaxy.

This makes a merging pair of galaxies with quasar activity hard to detect; it is difficult to separate the light from the two quasars because they are in such close proximity to each other. Also, observing a wide enough area of the sky to catch these rare events in sufficient numbers is a challenge.

To overcome these obstacles, the team took advantage of a sensitive wide survey of the sky using the Hyper Suprime-Cam (HSC) camera on the Subaru Telescope.

"To make our job easier, we started by looking at the 34,476 known quasars from the Sloan Digital Sky Survey with HSC imaging to identify those having two (or more) distinct centers," said lead author John Silverman of the Kavli Institute for the Physics and Mathematics of the Universe. "Honestly, we didn't start out looking for dual quasars. We were examining images of these luminous quasars to determine which type of galaxies they preferred to reside in when we started to see cases with two optical sources in their centers where we only expected one."

The team identified 421 promising cases. However, there was still the chance many of these were not bona-fide dual quasars but rather chance projections such as starlight from our own galaxy. Confirmation required detailed analysis of the light from the candidates to search for definitive signs of two distinct quasars.

Using Keck Observatory's Low Resolution Imaging Spectrometer (LRIS) and Gemini Observatory's Near-Infrared Integral Field Spectrometer, Silverman and his team identified three dual quasars, two of which were previously unknown. Each object in the pair showed the signature of gas moving at thousands of kilometers per second under the influence of a supermassive black hole.

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Beacon from the early universe

Often described as cosmic lighthouses, quasars are luminous beacons that can be observed at the outskirts of the Universe, providing a rich topic of study for astronomers and cosmologists. Now scientists have announced the discovery of the second-most distant quasar ever found, at more than 13 billion lightyears from Earth.

UC Santa Barbara's Joe Hennawi, a professor in the Department of Physics, and former UCSB postdoctoral scholars Frederick Davies and Feige Wang, provided crucial modeling and data analysis tools that enabled this discovery. The results are currently in preprint on ArXiv and will appear in The Astrophysical Journal Letters.

The researchers have named the object Pōniuā'ena, which means "unseen spinning source of creation, surrounded with brilliance" in the Hawaiian language. It is the first quasar to receive an indigenous Hawaiian name.

Quasars are incredibly bright sources of radiation that lie at the centers of distant massive galaxies. Matter spiraling onto a supermassive black hole generates tremendous amounts of heat making it glow at ultraviolet and optical wavelengths. "They are the most luminous objects in the Universe," Hennawi said, "outshining their host galaxies by factors of more than a hundred."

Since the discovery of the first quasar, astronomers have been keen to determine when they first appeared in our cosmic history. By systematically searching for these rare objects in wide-area sky surveys, astronomers discovered the most distant quasar (named J1342+0928) in 2018 and now the second-most distant, Pōniuā'ena (or J1007+2115).

The team first detected Pōniuā'ena as a possible quasar after combing through large area surveys. In 2019, the researchers observed the object using the W. M. Keck Observatory and Gemini Observatory on Mauna Kea, in Hawaii, confirming its existence and identity.

Pōniuā'ena is only the second quasar yet detected at a distance calculated at a cosmological redshift greater than 7.5, or 13 billion light years from Earth. It hosts a black hole twice as large as the other quasar known from the same era. The existence of these massive black holes at such early times challenges current theories of how supermassive black holes formed and grew in the young universe.

A cosmological puzzle

Spectroscopic observations from Gemini and Keck show the black hole powering Pōniuā'ena is 1.5 billion times more massive than our Sun. "Pōniuā'ena is the most distant object known in the universe hosting a black hole exceeding one billion solar masses," said lead author Jinyi Yang, a postdoctoral research associate at the University of Arizona.

Black holes grow by accreting matter. In the standard picture, supermassive black holes grow from a much smaller "seed" black hole, which could have been the remnant of a massive star that died. "So it is puzzling how such a massive black hole can exist so early in the universe's history because there does not appear to be enough time for them to grow given our current understanding," Davies explained.

For a black hole of this size to form this early in the universe, it would need to start as a 10,000-solar-mass seed black hole only 100 million years after the Big Bang -- as opposed to growing from a much smaller black hole formed by the collapse of a single star.

"How can the universe produce such a massive black hole so early in its history?" said Xiaohui Fan, at the University of Arizona. "This discovery presents the biggest challenge yet for the theory of black hole formation and growth in the early universe." The discovery of a more exotic mechanism to form the seed black hole may be required to explain the mere existence of Pōniuā'ena.

The Epoch of Reionization

Current theory holds that the birth of stars and galaxies as we know them started during the Epoch of Reionization. Beginning about 400 million years after the Big Bang, the diffuse matter in between galaxies went from being neutral hydrogen to ionized hydrogen. The growth of the first giant black holes is thought to have occurred during this time.

The discovery of quasars like Pōniuā'ena, deep in the reionization epoch, is a big step towards understanding this process of reionization and the formation of early supermassive black holes and massive galaxies. Pōniuā'ena has placed new and important constraints on the evolution of the intergalactic medium in the reionization epoch.

"Pōniuā'ena acts like a cosmic lighthouse. As its light travels the long journey towards Earth, its spectrum is altered by diffuse gas in the intergalactic medium which allowed us to pinpoint when the Epoch of Reionization occurred," said Hennawi. The modeling and data analysis method used to infer information about the Epoch of Reionization from these distant quasar spectra was developed in his research group at UC Santa Barbara with Davies and Wang.

"Through University of California Observatories, we have privileged access to the Keck telescopes on the summit of Mauna Kea, which allowed us to obtain high quality data on this object shortly after it was discovered using the Gemini telescope," Hennawi said.

Finding these distant quasars is a needle in a haystack problem. Astronomers must mine digital images of billions of celestial objects in order to find quasar candidates. "Even after you identify the candidates, the current success rate of finding them is about 1%, and this involves spending lots of expensive telescope time observing contaminants," Wang explained.

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Six galaxies undergoing sudden, dramatic transitions

Galaxies come in a wide variety of shapes, sizes and brightnesses, ranging from humdrum ordinary galaxies to luminous active galaxies. While an ordinary galaxy is visible mainly because of the light from its stars, an active galaxy shines brightest at its center, or nucleus, where a supermassive black hole emits a steady blast of bright light as it voraciously consumes nearby gas and dust.

Sitting somewhere on the spectrum between ordinary and active galaxies is another class, known as low-ionization nuclear emission-line region (LINER) galaxies. While LINERs are relatively common, accounting for roughly one-third of all nearby galaxies, astronomers have fiercely debated the main source of light emission from LINERs. Some argue that weakly active galactic nuclei are responsible, while others maintain that star-forming regions outside the galactic nucleus produce the most light.

A team of astronomers observed six mild-mannered LINER galaxies suddenly and surprisingly transforming into ravenous quasars -- home to the brightest of all active galactic nuclei. The team reported their observations, which could help demystify the nature of both LINERs and quasars while answering some burning questions about galactic evolution, in the Astrophysical Journal on September 18, 2019. Based on their analysis, the researchers suggest they have discovered an entirely new type of black hole activity at the centers of these six LINER galaxies.

"For one of the six objects, we first thought we had observed a tidal disruption event, which happens when a star passes too close to a supermassive black hole and gets shredded," said Sara Frederick, a graduate student in the University of Maryland Department of Astronomy and the lead author of the research paper. "But we later found it was a previously dormant black hole undergoing a transition that astronomers call a 'changing look,' resulting in a bright quasar. Observing six of these transitions, all in relatively quiet LINER galaxies, suggests that we've identified a totally new class of active galactic nucleus."

All six of the surprising transitions were observed during the first nine months of the Zwicky Transient Facility (ZTF), an automated sky survey project based at Caltech's Palomar Observatory near San Diego, California, which began observations in March 2018. UMD is a partner in the ZTF effort, facilitated by the Joint Space-Science Institute (JSI), a partnership between UMD and NASA's Goddard Space Flight Center.

Changing look transitions have been documented in other galaxies -- most commonly in a class of active galaxies known as Seyfert galaxies. By definition, Seyfert galaxies all have a bright, active galactic nucleus, but Type 1 and Type 2 Seyfert galaxies differ in the amount of light they emit at specific wavelengths. According to Frederick, many astronomers suspect that the difference results from the angle at which astronomers view the galaxies.

Type 1 Seyfert galaxies are thought to face Earth head-on, giving an unobstructed view of their nuclei, while Type 2 Seyfert galaxies are tilted at an oblique angle, such that their nuclei are partially obscured by a donut-shaped ring of dense, dusty gas clouds. Thus, changing look transitions between these two classes present a puzzle for astronomers, since a galaxy's orientation towards Earth is not expected to change.

Frederick and her colleagues' new observations may call these assumptions into question.

"We started out trying to understand changing look transformations in Seyfert galaxies. But instead, we found a whole new class of active galactic nucleus capable of transforming a wimpy galaxy to a luminous quasar," said Suvi Gezari, an associate professor of astronomy at UMD, a co-director of JSI and a co-author of the research paper. "Theory suggests that a quasar should take thousands of years to turn on, but these observations suggest that it can happen very quickly. It tells us that the theory is all wrong. We thought that Seyfert transformation was the major puzzle. But now we have a bigger issue to solve."

Frederick and her colleagues want to understand how a previously quiet galaxy with a calm nucleus can suddenly transition to a bright beacon of galactic radiation. To learn more, they performed follow-up observations on the objects with the Discovery Channel Telescope, which is operated by the Lowell Observatory in partnership with UMD, Boston University, the University of Toledo and Northern Arizona University. These observations helped to clarify aspects of the transitions, including how the rapidly transforming galactic nuclei interacted with their host galaxies.

"Our findings confirm that LINERs can, in fact, host active supermassive black holes at their centers," Frederick said. "But these six transitions were so sudden and dramatic, it tells us that there is something altogether different going on in these galaxies. We want to know how such massive amounts of gas and dust can suddenly start falling into a black hole. Because we caught these transitions in the act, it opens up a lot of opportunities to compare what the nuclei looked like before and after the transformation."

Unlike most quasars, which light up the surrounding clouds of gas and dust far beyond the galactic nucleus, the researchers found that only the gas and dust closest to the nucleus had been turned on. Frederick, Gezari and their collaborators suspect that this activity gradually spreads from the galactic nucleus -- and may provide the opportunity to map the development of a newborn quasar.

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