Tag Archives: supermassive black holes

Astronomers have discovered two pairs of quasars in the distant Universe, about 10 billion light-years from Earth. In each pair, the two quasars are separated by only about 10,000 light-years, making them closer together than any other double quasars found so far away. The proximity of the quasars in each pair suggests that they are located within two merging galaxies. Quasars are the intensely bright cores of distant galaxies, powered by the feeding frenzies of supermassive black holes. One of the distant double quasars is depicted in this illustration. International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva

Double trouble! Astronomers discover distant quasar pairs

Astronomers have observed two pairs of quasars in the distant Universe, closer together than any previously observed examples of similar pairings. The team followed the discovery–made with the Hubble Space Telescope and Gaia spacecraft–with spectroscopic observations made by the Gemini North Telescope.

The discovery is significant as it points towards the possible existence of supermassive black hole (SMBH) pairs. As the quasar pairs exist in merging galaxies, the finding also grants researchers an insight into how such events could have proceeded in the early Universe.

Astronomers have discovered two pairs of quasars in the distant Universe, about 10 billion light-years from Earth. In each pair, the two quasars are separated by only about 10,000 light-years, making them closer together than any other double quasars found so far away. The proximity of the quasars in each pair suggests that they are located within two merging galaxies. Quasars are the intensely bright cores of distant galaxies, powered by the feeding frenzies of supermassive black holes. One of the distant double quasars is depicted in this illustration. Labels point out the location of the quasars, the accretion disks (rings of material feeding each black hole), and the quasar host galaxies, which are in the process of merging.

It is the relatively close proximity between the quasars in the two pairings of just 10-thousand light-years that suggests to the astronomers that they belong to merging galaxies.

“We estimate that in the distant Universe, for every one thousand quasars, there is one double quasar,” says Yue Shen, an astronomer at the University of Illinois. “So finding these double quasars is like finding a needle in a haystack.”

Shen is the lead author of a paper published in the latest edition of the journal Nature Astronomy.

Quasars sit at the centre of galaxies in an area known as the active galactic nuclei (AGN) blasting out powerful jets of radiation. They are powered by SMBHs devouring material like gas and dust that surrounds them.

Quasars are so powerful that they profoundly affect the evolution of galaxies around them. This means that studying them is also a great way of learning how galaxies come together.

These particular quasars are 10-billion light-years from Earth meaning they existed just four billion years after the Big Bang. Double quasars are, in of themselves, rare, especially at such great distances. But, what makes these pairs particularly interesting is the fact they point to even rarer, hitherto undiscovered, SMBH binaries.

These two Hubble Space Telescope images reveal two pairs of quasars that existed 10 billion years ago and reside at the hearts of merging galaxies. (NASA/ STScI)

“This truly is the first sample of dual quasars at the peak epoch of galaxy formation that we can use to probe ideas about how supermassive black holes come together to eventually form a binary,” says Nadia Zakamska, Johns Hopkins University, part of the team that made the discovery.

Supermassive Implications

The team’s discovery will excite scientists currently involved in the search for SMBH binaries. Current theories suggest that as monstrous as they are these black holes, which are believed to lurk at the centre of most galaxies, do not always exist in isolation.

Alessandra De Rosa is a research astrophysicist at the National Institute of Astrophysics, Italy, and the author of a recent review paper which summarizes what we know thus far about SMBH pairs.

The animation shows the evolution of the merging between two galaxies with mass ratio of 0.25 (Galaxy mass 1 = 4 * Galaxy mass 2). Different phases can be identified, from the gravitational approach to the final coalescence of the galaxies and black holes contained in them. (Capelo, et al, 2015)

“Searching for high z dual Active Galactic Nuclei at such small separations is a fundamental piece of information to understand how SMBHs could form and grow and to probe what we know about galaxy formation and evolution,” DeRosa, who was not involved in the team’s study, tells ZME Science. “Moreover, these systems are the most direct precursors of binary SMBHs which are amongst the loudest emitters of gravitational waves in the low-frequency ranges.”

DeRosa continues by explaining that the search for these objects at such great distances is extremely challenging due to instrument limitations that prevent them from being individually distinguished.

Until now it has been believed that these pairings would find the black holes in such close proximity that they could only be distinguished by the gravitational waves launched by their eventual merger.

This new research could offer another way to at least study how such SMBH pairings come together and form binaries.

Tracking Down Quasar Pairs

As DeRosa points out, tracking down these quasar pairs at a distance of around 10-billion years was no easy task. In order to do this, the astronomers employed a novel new method that unites data from several space-based and ground-based telescopes.

It takes an extremely powerful telescope to view objects at such distances limiting the team’s choice to the Gemini North telescope in Hawai’i, and the Hubble Space Telescope. Because observing time on these telescopes is extremely limited, sweeping the entire sky for quasar pairs was out of the question.

This artist’s conception shows the brilliant light of two quasars residing in the cores of two galaxies that are in the chaotic process of merging. The gravitational tug-of-war between the two galaxies stretches them, forming long tidal tails and igniting a firestorm of star birth. (NASA/ STScI)

To work around this, the team selected 15 quasars from the 3D map created from data collected by the Sloan Digital Sky Survey (SDSS). Observations from the Gaia spacecraft were then used to narrow these 15 quasars to candidates that could actually be pairs.

The last step of the process was using Hubble to get a better look at these suspects. In this way, the team was able to confirm that two of the objects they selected were indeed quasar pairs.

Further investigation with Gemini North and its  Gemini Multi-Object Spectrograph (GMOS) instrument allowed the astronomers to resolve the quasars’ individual spectra. Locked within this light signature is information regarding the distance from Earth and the quasars’ compositions.

“The Gemini observations were critically important to our success because they provided spatially resolved spectra to yield redshifts and spectroscopic confirmations simultaneously for both quasars in a double,” says Yu-Ching Chen, part of the team and a graduate student at the University of Illinois. “This method unambiguously rejected interlopers due to chance superpositions such as from unassociated star-quasar systems.”

The Next Steps for Studying Quasar Pairs

Whilst the team is extremely confident that they have discovered quasar pairs in merging galaxies, there does remain the slight chance that they have actually captured a double image of a single quasar.

This kind of doppelganger illusion can be caused by strong gravitational lensing, the bending of light from a distant source when an object of great mass passes between it and our line of sight.

In extreme cases, this lensing can cause objects to appear at multiple points in the sky due to light being forced to take different paths across the Universe. Striking examples are so-called Einstein crosses and rings when single light sources appear at numerous points in a geometrical pattern.

An Einstein ring is an extreme example of gravitational lensing. The team are confident that this is not the source of their dual quasar discovery (ESA/Hubble & NASA)

The researchers believe that this can be discounted in the case of their research as the light from the distant quasars did not pass an intersecting foreground galaxy.

The next step for the researchers is the research for more quasar pairs, hopefully leading to the development of a census of such duos in the early universe.

“This proof of concept really demonstrates that our targeted search for dual quasars is very efficient,” Hsiang-Chih Hwang, the principal investigator of the Hubble observations and a graduate at John Hopkins University, concludes. “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.”

Do Black Holes Merge? (NASA/Public Domain)

Double Trouble! Hunting for Supermassive Black Hole Mergers

Supermassive black holes sat at the centre of active galaxies could have company. Binary pairs of these titanic cosmic objects could merge to form an even more monstrous black hole. Observational methods are finally becoming sensitive enough to spot such an event. 

The image of a supermassive black hole sat monolithic and alone at the centre of its galaxy, mercilessly swallowing any matter unfortunately enough to cross its path could be seriously challenged over the coming years. Theories of how galaxies grow and evolve and the role supermassive black holes play in these processes have long suggested that these objects may not dwell alone. In fact, not only may such spacetime events live in pairs, but after being brought together, they may merge in what could be the most powerful single event in the Universe, profoundly affecting its evolution.

Do Black Holes Merge? (NASA/Public Domain)
Artist’s impression of a violent merger between two supermassive black holes (NASA/ Pubic Domain)

“Astrophysical black holes are among the most fascinating objects in the Universe: they are ideal laboratories to study the fundamental laws of physics and one of the main drivers of the evolution of the Universe,” explains Alessandra De Rosa, a research astrophysicist at the National Institute of Astrophysics, Roma, Italy. “Understanding how they work and interact with their close environment, and unveil the physical conditions of the medium around them is one of the major challenges of 21st-century Astrophysics.”

Understanding the relationship between black holes and the galaxies that host them is key to building a model that satisfactorily describes the evolution of both. But, thus far evidence of this process is sparse. So, why are supermassive black hole mergers so hard to spot?

Hidden in Plain Sight. How Supermassive Black Hole Binaries and Mergers evade Observation

Despite the potential power of such a merger event, we haven’t as of yet managed to distinguish individual binary supermassive black holes or much evidence that such collisions occur. This is because these pairings and the mergers that may eventually arise from them lurk in what is known as the Active Galactic Nuclei (AGN) — compact regions at the centre of galaxies where the electromagnetic emissions dwarf that of the entire galaxy which surrounds it.

Because this emission — which occurs from the radio wave to the gamma-ray regions of the electromagnetic spectrum — is so powerful, astronomers believe that it does not arise as a result of stellar activity. Rather, they theorise that the powerful electromagnetic radiation emitted by the AGN is the result of at least one supermassive black hole accreting matter — a violent process in which dust, gas, and even stars are ripped apart in a violent and tremendously hot accretion disc surrounding a central supermassive black hole before falling onto what can roughly be described as its ‘surface.’

Here’s the problem; that electromagnetic emission is so overwhelmingly powerful and the AGN is so small in comparion to its host galaxy that there is no way that traditional astronomy — which relies on electromagnetic signals — alone, can distinguish the finer detail of this region. Finer detail that could reveal occupation by two, rather than just one, supermassive black holes.

“Currently, observational evidence for these pairs is almost non-existent,” De Rosa laments. “This can be explained if they quickly shrink to small separations and become impossible to be resolved with telescopes as pairs. So,  we must rely on indirect signatures.”

Fortunately, supermassive black hole mergers, if they occur, would not just be prodigious producers of electromagnetic radiation. They should also produce intense gravitational wave signals.

De Rosa is the lead author of a review paper published in the journal New Astronomy Reviews that looks both the history of our search for supermassive black hole binaries and puts forward a road map for future discovery of such events. The researcher emphasises the importance of ‘multimessenger astronomy’ — which combines traditional electromagnetic observations with the detection of gravitational waves, allowing astronomers to view the Universe in an entirely new way, thus making events and objects are previously hidden to them — events like black hole mergers — accessible.

But before examing mergers, it’s worth considering the truly epic processes that bring supermassive black hole pairings together in the first place.

Cosmic Matchmaking: Bringing Together Supermassive Black Holes

It may not be too surprising to find supermassive black holes hanging-out together in pairs, as our observations of the Universe thus far, show that stellar objects seem to prefer to hang out in pairs. These binary systems are far more common than single star systems such as our solar system, and three-star systems — the latter of which prove to be far too unstable.

“A binary supermassive black hole is made up of two supermassive black holes that are orbiting around each other,” says Julie Comerford, an Associate Professor in the Department of Astrophysical and Planetary Sciences at the University of Colorado, Boulder who specializes in the study of AGNs. “Such binary systems are common in the universe — around half of all stars are in binary systems, where two stars are orbiting around each other.”

As black holes evolve from such stellar objects, and these objects enjoy the company, it would seem intuitive to believe that black hole binaries should be fairly common. There’s a problem with that thinking though.

Only the most massive stars end their lives as black holes, and supermassive black holes are even rarer. Couple that with the fact that most binary systems contain a massive star coupled with a much smaller counterpart. Thus, It’s quite unlikely that two stars in the same binary system would both end up as supermassive black holes. In fact, after the transformation of the first star, it’s likely its partner will be stripped of material and left as a neutron star, a much smaller white dwarf, or destroyed entirely– possibly consumed by its counterpart.

So, if supermassive binaries aren’t likely to grow together, this means that some event must create this union– the merger of two galaxies.

“Each massive galaxy has a supermassive black hole at its centre, so the way you make a supermassive black hole binary is by merging two galaxies together,” Comerford tells ZME Science. “Each galaxy brings its own supermassive black hole to the merger, and as the galaxies combine the supermassive black holes begin their own dance of orbiting around each other.”

This means that spotting such a supermassive black hole binary would provide good evidence that the galaxy it occupies is the result of a merger, or even, that such a merger is still ongoing. It would also give us a hint at what is to come for our own galaxy. “This will one day happen to our Milky Way Galaxy — when it merges with the Andromeda Galaxy in about 4 billion years,” Comerford continues. “Our supermassive black hole and Andromeda’s supermassive black hole will form a binary!”

Mathematical modelling of these galaxy mergers seems to show that the process causes major gas inflow towards the central supermassive black hole — or black holes, as the case may be — this powers accretion and various nuclear processes activating the galactic nucleus. This inflow of gas, dust and other material could also result in the growth of the supermassive black hole.

“Astronomers believe that galaxies merge one or more times during their cosmological life,” says Alessandra De Rosa, who is is a research astrophysicist at the National Institute of Astrophysics, Roma, Italy. “These gigantic collisions are likely to be the primary process by which supermassive black holes are activated.”

Thus, galactic mergers aren’t just responsible for bringing supermassive black holes together, they also could kick start the feeding frenzy that makes an AGN the source of incredibly powerful radiation.

But what happens when these binary pairs of supermassive black holes form? Do they remain in a binary, or do they combine to form an even larger supermassive black hole? The merger of supermassive black holes to form larger objects would explain certainly one lingering cosmological question; how did these objects grow to such tremendous sizes in such a short period of time?

Despite the convenience of this phenomenon to tie up some loose cosmic-ends, we still don’t really know if it’s happening or not.

Using Gravitational Waves to Shed Light on Black Hole Binaries

After being brought together by a galaxy merger, when the supermassive black holes are very small separations, the gravitational waves that they emit carry away energy and enable the black holes to merge.

Thus, supermassive black holes at the centre of each galaxy are dragged close to each other, and eventually, form what is known as a dual active galactic nucleus. Theoretically, the final stage of this coming together — particularly if the black holes are gravitationally bound — will be the coalescence of these monsters in a merger that results in an even larger supermassive black hole. This merger would be accompanied by the emission of a gravitational-wave signal. Signals that thanks to the Laser Interferometer Gravitational-Wave Observatory LIGO, and its upcoming space-based counterpart Laser Interferometer Space Antenna (LISA), we can now theoretically detect.

“We think that binary supermassive black holes ultimately merge with each other and produce very energetic gravitational waves. In fact, supermassive black hole mergers are second only to the Big Bang as the most energetic phenomena in the Universe,” Comerford explains. The problem is, that even LIGO — responsible for the first detection of gravitational waves from colliding stellar-mass black holes — isn’t yet capable of detecting gravitational waves from merging supermassive black hole.

“These gravitational waves are too high frequency to be detected by LIGO, so they have not yet been detected,” Comerford adds. “But, we expect that pulsar timing arrays will detect gravitational waves from supermassive black hole mergers for the first time in just a few years.”

De Rosa concurs with the possible breakthrough in detecting gravitational waves from supermassive black hole mergers, highlighting not just the future contribution of pulsar timing arrays, but also, that of LISA — a space-based laser interferometer set to launch in 2034. “In the next decades, space-borne gravitational wave observatories, such as the next large mission of the European Space Agency, LISA, and experiments such as the Pulsar Timing Arrays, will provide first direct evidence of binary and merging SMBHs in the Universe,” she explains. 

For Comerford, the breakthrough new gravitational wave detection methods and multi-messenger astronomy stand poised to answer fundamental questions that have influenced her entire career. “When I was a graduate student, my group found some intriguing galaxy spectra that we thought might be produced by supermassive black hole pairs. I wondered if these unusual spectra could be the key to finding supermassive black hole binaries. I’ve been working on new and better ways to find supermassive black hole pairs ever since,” the researcher concludes. 

“I think the shocking thing is that we don’t actually know if supermassive black hole binaries merge! It could be that they just circle around each other and are not able to get close enough to each other where the gravitational waves can take over and make them merge. 

“When we detect gravitational waves from supermassive black holes, that will be the first time that we actually know that supermassive black hole binaries do merge.”


Sources and Further Reading 

De Rosa. A, Vignali. C, Bogdanovic. T, et al, ‘The Quest for Dual and Binary Supermassive Black Holes: A Multi-messenger View,” New Astronomy Reviews, [2020]. 

Astrophysicists find more evidence of ‘wandering’ black holes

Artist’s conception of a dwarf galaxy, its shape distorted, most likely by a past interaction with another galaxy, and a massive black hole in its outskirts (pullout). The black hole is drawing in material that forms a rotating accretion disc and generates jets of material propelled outward. Image credit: Sophia Dagnello, NRAO/AUI/NSF

Dwarf galaxies have traditionally been considered too small to host massive black holes, but new research emerging from Montanna State University (MSU) has revealed dozens of examples. The research, published in the Astrophysical Journal has delivered another surprise, these black holes aren’t located where scientists usually expect to find them.

“All of the black holes I had found before were in the centres of galaxies,” says Amy Reines, an assistant professor in the Department of Physics in the College of Letters and Science. “These were roaming around the outskirts. I was blown away when I saw this.”

Reines and her team searched 111 dwarf galaxies within a radius of a billion-light-years of Earth using the National Science Foundation’s Karl G. Jansky Very Large Array at the National Radio Astronomy Observatory, Albuquerque, New Mexico. During the course of their search, they identified 13 galaxies that very probably host black holes, the majority of which were not centralised. 

Reines is also a researcher in the MSU’s eXtreme Gravity Institute, which unites astronomers and physicists in order to study phenomena in which the gravitational influence is so powerful that it blurs the separation of space and time. This includes events and objects such as neutron stars, black holes, mergers and collisions between the two and even, the initial extreme period of rapid expansion of the universe — the big bang. 

The researcher explains that whilst stellar-mass black holes — those with a mass of up to 10 times that of our Sun — form as large stars undergo gravitational collapse, we are, thus far, uncertain how supermassive black holes form. This class of black hole which can have masses of up to billions of times that of the Sun is most commonly found in the centre of galaxies. 

This is certainly the case with our galaxy, the Milky Way, which hosts the supermassive black hole Sagittarius A* (SgrA*) at its centre. Dwarf galaxies are smaller than spiral galaxies like the Milky Way, containing a few billion stars rather than 100–400 billion as spiral galaxies tend to.

The results collected by Reines confirm computer simulations generated by Jillian Bellovary, assistant professor at Queensborough Community College, New York and Research Associate at the American Museum of Natural History. 

How black holes get lost

Bellovary’s computer simulations suggested that black holes could be disturbed from the centre of dwarf galaxies by interactions they undergo as they travel through space. This result coupled with Reines’ study have the potential to change the way we look for black holes in dwarf galaxies going forward. This change in thinking could also impact theories of how both dwarf galaxies and supermassive black holes form. 

“We need to expand searches to target the whole galaxy, not just the nuclei where we previously expected black holes to be,” Reines adds.

No stranger for the search for black holes, Reines has been hunting these events for a decade, ever since she was a graduate student at the University of Virginia. Whilst she initially focused on star formation in dwarf galaxies, her research led her to something else that captured her interest: a massive black hole “in a little dwarf galaxy where it wasn’t supposed to be.”

Henize 2–10: a dwarf galaxy that hides a massive secret ( Reines et al. (2011))
Henize 2–10: a dwarf galaxy that hides a massive secret ( Reines et al. (2011))

The little dwarf galaxy she refers to is Heinze 2–10, located 30-million-light-years from Earth, which had previously been believed too small to host a massive black hole. “Conventional wisdom told us that all massive galaxies with a spheroidal component have a massive black hole and little dwarf galaxies didn’t,” Reines explains, adding that when she discovered such a relationship it was a “eureka” moment. After publishing these findings in the journal Nature she continued searching for further black holes in dwarf galaxies. “Once I started looking for these things on purpose, I started finding a whole bunch,” Reines says.

Visible-light images of galaxies that VLA observations showed to have massive black holes. Center illustration is artist’s conception of the rotating disk of material falling into such a black hole, and the jets of material propelled outward. Image credit: Sophia Dagnello, NRAO/AUI/NSF; DECaLS survey; CTIO
Visible-light images of galaxies that VLA observations showed to have massive black holes. Center illustration is artist’s conception of the rotating disk of material falling into such a black hole, and the jets of material propelled outward. Image credit: Sophia Dagnello, NRAO/AUI/NSF; DECaLS survey; CTIO

Changing her tactics by shifting from visual data from radio signals, Reines uncovered over 100 possible black holes in her first search of a sample that included 40,000 dwarf galaxies. In current search, as described in the latest paper, Reines returned to radio searches, hunting for radio signatures with that sample. This, she says, should allow her to find massive black holes in star-forming dwarf galaxies, even though she has only found one thus far. 

“When new discoveries break our current understanding of the way things work, we find even more questions than we had before,” comments Yves Idzerda, head of the Department of Physics at MSU.

As for Reines, the search continues. 

“There are lots of opportunities to make new discoveries because studying black holes in dwarf galaxies is a new field,” she said. “People are definitely captivated by black holes. They’re mysterious and fascinating objects.”

Original research: https://iopscience.iop.org/article/10.3847/1538-4357/ab4999

This is an artist's impression of planets orbiting a supermassive black hole. (Kagoshima University)

Planets could orbit Supermassive Black Holes

This is an artist's impression of planets orbiting a supermassive black hole. (Kagoshima University)
This is an artist’s impression of planets orbiting a supermassive black hole. (Kagoshima University)

The idea of stars orbiting the supermassive black holes that researchers believe lurk at the centre of most galaxies has been long established as a matter of fact in science. In ‘active galactic nuclei’ or AGNs, these black holes are surrounded by haloes of gas and dust in a violent churning environment. Such clouds of gas and dust have the potential to birth not only stars but planets as well. Yet, the question of whether planets can also orbit these spacetime events has yet to be established. 

Enter Keiichi Wada, a professor at Kagoshima University, and Eiichiro Kokubo, a professor at the National Astronomical Observatory of Japan. These scientists from the distinct fields of active galactic nuclei research and planet formation research respectively have calculated that as a result of gas disc growth, an entirely new class of planets may form around supermassive black holes. 

“With the right conditions, planets could be formed even in harsh environments, such as around a black hole,” Wada points out. 

In their research published in the Astrophysical Journal, the duo of theoreticians propose that protoplanetary discs that surround young stars may not be the only potential site for planet formation. The researchers instead focused calculations and mathematical models on the denser dust discs found around supermassive black holes in AGNs, thus arriving at a surprising conclusion. 

“Our calculations show that tens of thousands of planets with 10 times the mass of the Earth could be formed [at a distance of] around 10 light-years from a black hole,” says Eiichiro Kokubo. 

“Around black holes, there might exist planetary systems of astonishing scale.”

One of the hindrances to the formation of planets in such discs of dust has previously been the amount of energy generated in AGNs, Researchers had believed that this energy output would prevent the coagulation of ‘fluffy ice dust’ that can help the growth of dust grains that can lead to planet formation in protoplanetary discs.

But, what Wada and Kokubo discovered was that the huge density of dust discs around supermassive black holes in AGNs —potentially containing as much as a hundred thousand times the mass of the Sun worth of dust, which is a billion times more massive than a typical protoplanetary disc — helps protect the outer layers from bombardment from high-energy radiation such as gamma rays. 

 A schematic picture of the Active Galactic Nucleus (AGN) and the circumnuclear disc. (Wada, Kokubo, 2019)
A schematic picture of the Active Galactic Nucleus (AGN) and the circumnuclear disc. (Wada, Kokubo, 2019)

This helps form a low-temperature region similar to that found in protoplanetary discs, and thus, in turn, increases the likelihood of fluffy deposits building.

The process would lead to the formation of planets within a period of several hundred million years, according to the pair, and also result in much denser and more populated collections of planets. 

Unfortunately, the limits of current methods of identifying exoplanets would make identifying planets around a supermassive black hole challenging to say the least. 

“ Doppler spectroscopy, transit photometry, gravitational micro-lensing, or direct imaging are hopeless,” warn the duo in their paper. They go on to suggest that a method called photometry with an x-ray interferometer located in space could be a possible solution — if a way of distinguishing the effect caused by such planets from the natural variability of the AGN can be developed. 

For now, researchers will have to look to mathematical models alone to theorise about the potential for planets in orbit around black holes. 


Original research: https://arxiv.org/pdf/1909.06748.pdf

Ancient galaxies from the study are visible to ALMA (right) but not to Hubble (left). Credit: © 2019 Wang et al.

‘Hidden’ ancient galaxies discovery may redefine our understanding of the Universe

The discovery of 39 ‘hidden’ ancient galaxies urges scientists to rethink their theories of fundamental aspects of the Universe — including supermassive black holes, star formation rates, and the ever-elusive, dark matter.

Ancient galaxies from the study are visible to ALMA (right) but not to Hubble (left). Credit: © 2019 Wang et al.

In an unprecedented discovery of astronomers, researchers have utilised the combined power of a multitude of observatories across the globe to discover a vast array of 39 previously hidden galaxies.

The finding — described by the researchers from the University of Tokyo as a ‘treasure trove’ — is the first multiple discoveries of this kind. But the finding is significant for more than its size alone.

In addition to containing a wealth of newly discovered ancient galaxies, an abundance of this particular type of galaxy suggests that scientists may have to refine current models of the universe.

This is because our current understanding of the universe and how it formed is built upon observations of galaxies in ultraviolet light. But observations in these wavelengths under-represent the most massive galaxies — those with high dust content and crucially, the most ancient.

This means that a discovery of such galaxies — such as the one just made — must force us to reconsider the rates of star formation in the early universe. The study explains that the population of stars discovered may mean that star formation rates were actually ten times greater in early epochs than previous estimates held.

There are also particular ramifications for our understanding of both supermassive black holes and their distribution, and for the concept of dark matter — the elusive substance which makes up 80% of the matter in the universe.

Despite the wealth of astronomical data that has become available to scientists since the launch of the Hubble Space Telescope, researchers at the Institute of Astronomy in Toyko were aware there were things that Hubble simply couldn’t show us. It was these things — fundamental pieces of the cosmic puzzle — that they wanted to investigate.

They achieved this by unifying different observatories, using them to look more deeply in the Universe than Hubble alone could do. This is what led them to this huge collection of galaxies.

Researcher Tao Wang describes the uniqueness and magnitude of the team’s discovery: “This is the first time that such a large population of massive galaxies was confirmed during the first two billion years of the 13.7-billion-year life of the universe.

“These were previously invisible to us.”

Wang continues: “This finding contravenes current models for that period of cosmic evolution and will help to add some details, which have been missing until now.”

A different view of the universe

Wang explains that if we could see these galaxies and the light they shed, our view from the Milky way would be significantly different: “For one thing, the night sky would appear far more majestic. The greater density of stars means there would be many more stars close by appearing larger and brighter.

“But conversely, the large amount of dust means farther-away stars would be far less visible, so the background to these bright close stars might be a vast dark void.”

The galaxies have been difficult to see from Earth due to how faint they are. Were we able to see these stars, their density would make the night sky majestic, Wang says.

The light from these galaxies also has to battle extinction — the absorption of light) by intervening interstellar dust clouds. The light from the galaxies also has to travel great distances meaning the wavelength is redshifted by the expansion of the universe making it even less visible.

Professor Kotaro Kohno. Credit: © 2019 Rohan Mehra — Division of Strategic Public Relations

Professor Kotaro Kohno explains that this phenomenon is how the galaxies escaped Hubble’s gaze: “The light from these galaxies is very faint with long wavelengths invisible to our eyes and undetectable by Hubble.

“So we turned to the Atacama Large Millimeter/submillimeter Array (ALMA), which is ideal for viewing these kinds of things. I have a long history with that facility and so knew it would deliver good results.”

This redshift due to cosmic expansion does have its advantages, however. It allows astronomers to estimate not just the distances to the galaxies in question, but it also allows them to calculate just how long ago the light was emitted.

The hidden implications of these hidden galaxies

The team’s finding is so controversial and poses such a radical rethink that they found their fellow astronomers were initially reluctant to believe they had found what they claimed.

A few of the 66 radio telescope antennas that make up ALMA. Credit: © 2019 Kohno et al.

Wang explains: “It was tough to convince our peers these galaxies were as old as we suspected them to be. Our initial suspicions about their existence came from the Spitzer Space Telescope’s infrared data.

“But ALMA has sharp eyes and revealed details at submillimeter wavelengths, the best wavelength to peer through dust present in the early universe. Even so, it took further data from the imaginatively named Very Large Telescope in Chile to really prove we were seeing ancient massive galaxies where none had been seen before.”

The discovery has the potential to reshape our ideas of the supermassive black holes that scientists currently believe nestle at the centre of most galaxies.

Kohno elaborates: “The more massive a galaxy, the more massive the supermassive black hole at its heart.

“So the study of these galaxies and their evolution will tell us more about the evolution of supermassive black holes, too.”

Kohno also explains that some ideas regarding dark matter may have to be revised, too: “Massive galaxies are also intimately connected with the distribution of invisible dark matter. This plays a role in shaping the structure and distribution of galaxies. Theoretical researchers will need to update their theories now.”

In addition to the potential shake up the team believes that their findings may already present, they expect more surprises to come.

Wang concludes: These gargantuan galaxies are invisible in optical wavelengths so it’s extremely hard to do spectroscopy, a way to investigate stellar populations and chemical composition of galaxies. ALMA is not good at this and we need something more.

“I’m eager for upcoming observatories like the space-based James Webb Space Telescope to show us what these primordial beasts are really made of.”


Original research: T. Wang, C. Schreiber, D. Elbaz, Y. Yoshimura, K. Kohno, X. Shu, Y. Yamaguchi, M. Pannella, M. Franco, J. Huang, C.F. Lim & W.H. Wang. A dominant population of optically invisible massive galaxies in the early Universe. Nature. DOI: 10.1038/s41586–019–1452–4

Supermassive black holes eventually stop star formation

Researchers analyzed the correlation between the mass of supermassive black hole and the history of star formation in its galaxy. They found that the bigger the black hole is, the harder it is for the galaxy to generate new stars.

Scientists have been debating this theory for a while, but until now, they lacked enough observational data to prove or disprove it.

Via Pixabay/12019

Researchers from the University of Santa Cruz, California used data from previous studies measuring supermassive black hole mass. They then used spectroscopy to determine how stars formed in galaxies featuring such gargantuan black holes and correlate the two.

Spectroscopy is a technique that relies on measuring the wavelength of light emerging from objects — stars, in this case. The paper’s lead author Ignacio Martín-Navarro used computational analysis to determine how the black holes affected star formation — in a way, he tried to solve a light puzzle.

“It tells you how much light is coming from stellar populations of different ages,” he said in a press release.

Via Pixabay / imonedesign.

Next, the research team plotted the size of supermassive black holes and compared them to a history of star formation in that galaxy. They found that as the black holes grew more and more, star formation was significantly slowed down. Other characteristics of the galaxies, such as shape or size, were found irrelevant to the study.

“For galaxies with the same mass of stars but different black hole mass in the center, those galaxies with bigger black holes were quenched earlier and faster than those with smaller black holes. So star formation lasted longer in those galaxies with smaller central black holes,” Martín-Navarro said.

Star gas from Carina Nebula, source: Pixabay/skeeze

Scientists still trying to determine why this happens. One theory suggests that the lack of cold gas is the main culprit for reduced star formation. The supermassive black holes suck in the nearby gas, creating high-energy jets in the process. These jets ultimately expel cold gas from the galaxy. Without enough cold gas, there is no new star formation, so the galaxy becomes practically sterile.

In the press release, co-author Aaron Romanowsky concluded:

“There are different ways a black hole can put energy out into the galaxy, and theorists have all kinds of ideas about how quenching happens, but there’s more work to be done to fit these new observations into the models.”

The paper was published in Nature on the 1st of January 2018.

Oldest black hole found by astronomers — the gargantuan object lies 13 billion light years away from us

The supermassive black hole emerged when the universe was still in its infancy, and it took light carrying its image 13 billion years to reach us. The process which led to its formation is completely unknown.

Artist’s impression of a quasar, an active supermassive black hole with a very high luminosity. Image credits: ESO/M. Kornmesser.

The object was discovered by Eduardo Bañados, an astronomer at Carnegie, as he was looking through multiple all-sky surveys — maps of the distant universe. He was stunned. With a whopping mass, 800 times larger than that of our Sun, the black hole is almost as old as the world itself. The universe is an estimated 13.8 billion years, and this black hole appeared just 690 million years after the Big Bang. It’s the oldest and most distant object we’ve ever seen.

“This is the only object we have observed from this era,” says Robert Simcoe, the Francis L. Friedman Professor of Physics in MIT’s Kavli Institute for Astrophysics and Space Research. “It has an extremely high mass, and yet the universe is so young that this thing shouldn’t exist. The universe was just not old enough to make a black hole that big. It’s very puzzling.”

It’s not just that the black hole formed during these early times, it’s that the universe was undergoing a major shift at that point. During its early stage, the universe went through what is sometimes called the Dark Age — not a metaphor, as it is for the human period, but a truly a dark age as there was no light. The universe was opaque or “foggy” as photons were interacting with early protons and electrons. Light from that age is not visible to us.

Artist’s conceptions of the most-distant supermassive black hole ever discovered, which is part of a quasar from just 690 million years after the Big Bang. It is surrounded by neutral hydrogen, indicating that it is from the period called the epoch of reionization, when the universe’s first light sources turned on. Image: Robin Dienel (Courtesy of the Carnegie Institution for Science), via MIT.

When this black hole was formed, the universe was transitioning from this dark phase into something more similar to what we see today. More and more stars were forming, eventually generating enough radiation to flip hydrogen from neutral (in which electrons are bound to the nucleus) to ionized (in which electrons are freer to interact). This shift allowed light to pass through the cosmos, eventually reaching a tiny blue dot we call Earth and allowing us to research things far away — both in space and in time. Astronomers believe that the black hole was formed in a universe which was about half neutral and half ionized.

“What we have found is that the universe was about 50/50 — it’s a moment when the first galaxies emerged from their cocoons of neutral gas and started to shine their way out,” Simcoe says. “This is the most accurate measurement of that time, and a real indication of when the first stars turned on.”

It’s the first time we are able to detect something this old, and the prospect is exciting as it offers us a unique glimpse into the past. But the massive black hole also comes with a massive mystery. Black holes take on different shapes and sizes, but most often, they form when a massive star collapses onto itself. But at a time when stars were just starting to light up, they wouldn’t have had the time and mass to form such a black hole.

“If you start with a seed like a big star, and let it grow at the maximum possible rate, and start at the moment of the Big Bang, you could never make something with 800 million solar masses — it’s unrealistic,” Simcoe says. “So there must be another way that it formed. And how exactly that happens, nobody knows.”

To make things even more interesting, this appears to be a supermassive black hole — the most massive known objects in the universe, the likes of which are thought to lie at the center of all galaxies. It’s also very active, devouring material at the center of a galaxy and emitting tremendous light in the process. This classifies it as a quasar, and it’s largely what allowed astronomers to discover it.

“Quasars are among the brightest and most distant known celestial objects and are crucial to understanding the early Universe,” said co-author Bram Venemans of the Max Planck Institute for Astronomy in Germany.

The process that led to the creation of this object remains unknown and will no doubt have theorists busy for years to come.

The study was published in Nature.

NASA pinpoints black holes that send out high-energy X-rays for first time ever

For the first time ever, NASA’s Chandra mission has pinpointed large numbers of black holes that send out high-energy X-rays. Although these unique black holes possess the highest pitched “voices” compared to their lower energy counterparts, until now they have remained elusive.

The blue dots in the above picture represent galaxies that contain supermassive black holes emitting high-energy X-rays. Credit: NASA/JPL-Caltech

The blue dots in the above picture represent galaxies that contain supermassive black holes emitting high-energy X-rays. Credit: NASA/JPL-Caltech

Prior to the current findings, NASA’s Chandra mission has been able to determine many of the black holes that contribute to the X-ray background, but not those that release high-energy X-rays.

The discovery of a large number of black holes that release these high-energy X-rays brings scientists closer to understanding the high-energy X-ray background created by the cosmic choir of black holes in space with the highest voices.

“We’ve gone from resolving just two percent of the high-energy X-ray background to 35 percent,” said Fiona Harrison of Caltech and lead author the upcoming new study describing the findings. “We can see the most obscured black holes, hidden in thick gas and dust.”

Understanding the X-ray background is essential to shed light on the growth patterns of supermassive black holes and the galaxies that they lie in. High-energy X-rays in particular reveal what lies around obscured supermassive black holes that are otherwise difficult to observe and can help determine the distribution of gas and dust that feed and hide these phenomena.

The NuSTAR telescope is the first to be capable of capturing high-energy X-rays into clear pictures and will no doubt be integral in building a more comprehensive picture of the X-ray background using data from these hidden high-energy black holes.

“Before NuSTAR, the X-ray background in high-energies was just one blur with no resolved sources,” Harrison said. “To untangle what’s going on, you have to pinpoint and count up the individual sources of the X-rays.”

“We knew this cosmic choir had a strong high-pitched component, but we still don’t know if it comes from a lot of smaller, quiet singers, or a few with loud voices,” said Daniel Stern of NASA’s Jet Propulsion Laboratory and co-author of the study. “Now, thanks to NuSTAR, we’re gaining a better understanding of the black holes and starting to address these questions.”

The findings will be published in an upcoming issue of The Astrophysical Journal. The data can currently be viewed on the pre-print server arXiv.org.