# Quasars and SMBH

Quasars are known to contain supermassive Black Holes at their cores. So does that mean that the number of quasars is equal to that of the SMBHs out there?

It means that the number of quasars must be less than or equal to the number of SMBH out there. It's believed that supermassive black holes are found at the center of most galaxies and the SMBH mass correlates with the velocity distribution of stars in the galaxy.

However, quasars only form in particularly large and active galaxies. Or perhaps particularly massive galaxies can only form around and be supported by particularly massive black holes? Regardless, based on this, while every quasar must possess a supermassive black hole, not every supermassive black hole is part of a system that contains a quasar.

Not really. Quasars do indeed need a SMBH to be powered, and this is a necessary condition.

But, Quasar phase only lasts for tens millions to few billions years. This means that, in a more recent universe, Quasars are turned off but the host galaxy… is still there. And the SMBH also do.

This is exactly as our Galaxy case ($Sgr A^*$), where the evidences for the presence of a SMBH are among the strongest ones, but still no nuclear activity is present.

However, there are tons of study to infer the proper amount of AGNs in the whole Universe by using luminosity functions.

Very good question. The number of quasars must be less than the number of SMBHs, since many galaxies, such as our own, contain SMBHs at their core (Sagittarius A*) and they are not classified as quasars (i.e., some galaxies are quiescent for whatever reason). Quasars represent an ultra-luminous active phase of gas accretion onto the SMBH. Such larger luminosities is believed to be caused by intense gas accretion triggered by major massive scale mergers between galaxies.

As such, Quasars are short lived events, and the SMBHs outlive the quasar (the lifetime of a quasar is of the order of 10$^6$-10$^9$ yr whereas the lifetime of a SMBH is much greater than the Hubble time). Hence, once the gas is all but consumed by such intense accretion the Quasar will slowly become quiescent. Hence why many galaxies contain SMBHs at their cores, but are no longer active.

## VLT detects most distant quasar with powerful radio jets

Quasars or quasi-stellar objects (QSOs) are the extremely bright astronomical objects that reside at the centres of distant galaxies and are powered by the gas spiralling at extremely high velocity into a supermassive black hole (SMBH).

The brightest quasars can even outshine their host galaxies.

As the gas in the disk spirals towards the SMBH, energy is released in the form of electromagnetic radiation, which can be detected across the electromagnetic spectrum.

Now, with the help of the European Southern Observatory's (ESO) Very Large Telescope (VLT), scientists have spotted the most distant source of radio emissions to date.

This newly discovered source was traced to a “radio-loud” quasar and has been nicknamed P172+18. It is an exceptionally bright object with extremely powerful jets emitting at radio wavelengths.

P172+18 is so distant from us that its light has taken thirteen billion years to reach Earth, that means scientists see it from the time when the Universe was only about 780 million years old.

While scientists have already discovered QSOs farther than P172+18, but this is the first time that a quasar with powerful radio jets have been identified in the ancient Universe.

Out of all discovered quasars so far, only about ten percent of them have jets. Scientists classify them as “radio-loud” and they shine brightly at radio frequencies.

Quasar P172+18 is powered by a black hole which is about three hundred million times more massive than our own Sun.

This black hole is consuming the matter very rapidly, and growing in mass at one of the highest rates ever spotted.

Scientists suspect that there is a link between the fast growth of SMBHs and the intense radio jets observed in QSOs like P172+18. These jets are believed to have the ability to disturb the matter around the SMBH and increase the rate at which matter falls in.

Thus, studying radio-loud quasars could help in understanding how black holes from the ancient Universe evolve into SMBHs so quickly after the Big Bang.

After having been identified as radio source, P172+18 was first recognized as a far away quasar by the Magellan Telescope at Las Campanas Observatory in Chile. However, short observation time did not allow scientists to study the object in detail.

Scientists then made more deep and detailed observations with the other ground based telescopes, including ESO’ VLT, National Radio Astronomy Observatory's Very Large Array and the Keck Telescope in the United States.

These observations allowed scientists to determine the key features such as the mass of the black hole and how fast it’s consuming the matter from its surroundings.

Scientists believe that P172+18 could be the first of many such radio loud quasars waiting to be discovered, perhaps at even greater cosmological distances, which they hope to locate with facilities such as ALMA and upcoming ESO’s Extremely Large Telescope (ELT).

## 'The Goblin' dwarf planet and an ancient quasar receive Hawaiian names

Two incredibly strange celestial objects whose discoveries trace, in part, to observatories at the summit of Maunakea now carry the peak with them in official names inspired by Hawaiian culture.

Their connection to Hawaii is all these two objects share. One is a quasar, a massive source of energy that scientists believe stems from a distant black hole — in this case, the quasar was born just 700 million years after the Big Bang and could contain the mass of 1.5 billion suns. The other object is much closer to us, a dwarf planet in our solar system that requires 40,000 years to complete a single orbit of our sun.

"We only want to name the really unique things, because there are literally like billions and billions and billions of things out there," Ka'iu Kimura, executive director of the 'Imiloa Astronomy Center, a museum and cultural center based in Hilo, Hawaii, that helps run the naming program, told Space.com in January at the 235th meeting of the American Astronomical Society.

The program, called A Hua He Inoa, is dedicated to finding Hawaiian names for astronomical objects discovered using the dozen telescopes atop Maunakea, at the heart of the island of Hawaii and a deeply contested site. But the program doesn't simply slap an existing name onto a discovery.

Instead, it brings astronomers and native Hawaiians — students, teachers or both — together to create a name grounded in traditions but tailored to the details of the discovery and how it resonates with a Hawaiian way of being in the universe. "You have to sit and explain to youth and hear their feedback," Kimura said of the scientists who have taken part. "We also put language and culture experts in that conversation."

An earlier version of the program, which relied more heavily on a specific Hawaiian language and cultural expert, most famously named the first interstellar asteroid to be discovered, now called 'Oumuamua, and the black hole that scientists released an image of last spring, called Pōwehi.

More recently, the International Astronomical Union, which oversees all celestial naming, adopted Hawaiian names developed through the program for two asteroids. Now, with the newly discovered quasar and the dwarf planet, the tally has reached a half dozen objects.

The group of Hawaiian teachers who developed the new name for the quasar, Pōniuāʻena, which would otherwise be referred to as J1007+2115, were inspired by the name Pōwehi to begin with "pō." In both names, the syllable represents the deep darkness of a black hole and derives from the Kumulipo, a native Hawaiian chant which tells the story of the creation of the islands.

But a quasar has brightness as well as darkness, which the teachers incorporated into the name.

"They were so impressed by the look and the motion of the quasar and how it's spewing out all of these heat and light," Kimura said of the participants. "It's spinning so fast and so radiantly that it glows brilliantly." That's where the latter portion of the name comes from, she said. "The name, Pōniuāʻena, evokes the unseen spinning source of creation, surrounded by brilliance," a statement from 'Imiloa explains.

The discovery was made using data from three different facilities atop Maunakea: W. M. Keck Observatory, the International Gemini Observatory and the University of Hawaii-owned United Kingdom Infrared Telescope.

Scientists first discovered the other newly named object, in 2015 using Japan's Subaru Telescope on the mountain. Before it earned an official name, the dwarf planet was nicknamed The Goblin, inspired by the letters TG in its arbitrary designation based on scientists' first observations of it.

While it's in our solar system, the dwarf planet isn't particularly neighborly. At its closest, the object comes within about 65 astronomical units (AU) — 1 AU is the average distance between the Earth and the sun, about 93 million miles or 150 million kilometers at the most distant point in its orbit, it strays about 2,300 AU away from the sun. It lies out beyond Pluto and traces a long orbit around the sun, with one year on the body lasting about 40,000 Earth years.

It's that epic journey around the sun that inspired the new Hawaiian name for the object, Leleākūhonua, that a group of students developed through the program. "The kids were inspired by this bird, the kolea," Kimura said, referring to a species also known as the Pacific Golden-Plover.

The plover spends its summers in Alaska and its winters in Hawaii, clocking as much as 2,000 miles (3,200 kilometers) in a single flight, according to the National Audubon Society. For the students in the naming program, that sounded an awful lot like the dwarf planet.

"They only come here once a year," Kimura said of the plovers. "They feed and they get a little chubbier and then they fly back," much like how the dwarf planet gains energy when it is closer to the sun, before migrating back out to the icy reaches of the solar system. The name Leleākūhonua was approved by the International Astronomical Union and announced on June 3.

For Kimura, each of these new names is about recognizing the unique culture and tradition of the Hawaiian islands, and honoring the fact that context can influence the science done in such a place. But names aren't enough for her, even names that are chosen with such a detailed process.

"To me, the win would be we'd see more Hawaiian students getting into science, we would see more and hear more of our language and our culture being spoken at these places of research," Kimura said. "We would promote globally the uniqueness of Hawaii, which really is its people, its language, its culture, and if astronomy can help give Hawaii — and any community that it is being done in across the world — that kind of recognition, honor and promotion, that is I think a big win."

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The space.com report said, "Their connection to Hawaii is all these two objects share. One is a quasar, a massive source of energy that scientists believe stems from a distant black hole — in this case, the quasar was born just 700 million years after the Big Bang and could contain the mass of 1.5 billion suns. The other object is much closer to us, a dwarf planet in our solar system that requires 40,000 years to complete a single orbit of our sun."

Interesting report. The quasar with SMBH of 1.5 billion solar masses, could have a diameter 59.22 AU. This SMBH formed about 700 million years after the BB event according to the report. Another report was out this week where a SMBH is 34 billion solar masses with quasar and redshift a bit larger than 4.6. That SMBH has a diameter somewhat larger than 1342 AU. The BB cosmology has trouble explaining the origin of SMBHs appearing so early in the history of the universe, shortly after the BB. It would be good to see a complete inventory list of all SMBH documented like we have for exoplanets confirmed.

The space.com report said, "Their connection to Hawaii is all these two objects share. One is a quasar, a massive source of energy that scientists believe stems from a distant black hole — in this case, the quasar was born just 700 million years after the Big Bang and could contain the mass of 1.5 billion suns. The other object is much closer to us, a dwarf planet in our solar system that requires 40,000 years to complete a single orbit of our sun."

Interesting report. The quasar with SMBH of 1.5 billion solar masses, could have a diameter 59.22 AU. This SMBH formed about 700 million years after the BB event according to the report. Another report was out this week where a SMBH is 34 billion solar masses with quasar and redshift a bit larger than 4.6. That SMBH has a diameter somewhat larger than 1342 AU. The BB cosmology has trouble explaining the origin of SMBHs appearing so early in the history of the universe, shortly after the BB. It would be good to see a complete inventory list of all SMBH documented like we have for exoplanets confirmed.

## New Method for Researching Activity Around Quasars and Black Holes

Ever since the discovery of Sagittarius A* at the center of our galaxy, astronomers have come to understand that most massive galaxies have a Supermassive Black Hole (SMBH) at their core. These are evidenced by the powerful electromagnetic emissions produced at the nuclei of these galaxies – which are known as “Active Galatic Nuclei” (AGN) – that are believed to be caused by gas and dust accreting onto the SMBH.

For decades, astronomers have been studying the light coming from AGNs to determine how large and massive their black holes are. This has been difficult, since this light is subject to the Doppler effect, which causes its spectral lines to broaden. But thanks to a new model developed by researchers from China and the US, astronomers may be able to study these Broad Line Regions (BLRs) and make more accurate estimates about the mass of black holes.

The study, “Tidally disrupted dusty clumps as the origin of broad emission lines in active galactic nuclei“, recently appeared in the scientific journal Nature. The study was led by Jian-Min Wang, a researcher from the Institute of High Energy Physics (IHEP) at the Chinese Academy of Sciences, with assistance from the University of Wyoming and the University of Nanjing.

An artist’s impression of the accretion disc around the supermassive black hole that powers an active galaxy. Credit: NASA/Dana Berry, SkyWorks Digital

To break it down, SMBHs are known for having a torus of gas and dust that surrounds them. The black hole’s gravity accelerates gas in this torus to velocities of thousands of kilometers per second, which causes it to heat up and emit radiation at different wavelengths. This energy eventually outshined the entire surrounding galaxy, which is what allows astronomers to determine the presence of an SMBH.

As Michael Brotherton, a UW professor in the Department of Physics and Astronomy and a co0author on the study, explained in a UW press release:

“People think, ‘It’s a black hole. Why is it so bright?’ A black hole is still dark. The discs reach such high temperatures that they put out radiation across the electromagnetic spectrum, which includes gamma rays, X-rays, UV, infrared and radio waves. The black hole and surrounding accreting gas the black hole is feeding on is fuel that turns on the quasar.”

The problem with observing these bright regions comes from the fact that the gases within them are moving so quickly in different directions. Whereas gas moving away (relative to us) is shifted towards the red end of the spectrum, gas that is moving towards us is shifted towards the blue end. This is what leads to a Broad Line Region, where the spectrum of the emitted light becomes more like a spiral, making accurate readings difficult to obtain.

Currently, the measurement of the mass of SMBHs in active galactic nuclei relies the “reverberation mapping technique”. In short, this involves using computer models to examine the symmetrical spectral lines of a BLR and measuring the time delays between them. These lines are believed to arise from gas that has been photoionized by the gravitational force of the SMBH.

Dense clouds of dust and gas, illustrated here, can obscure less energetic radiation from an active galaxy’s central black hole. High-energy X-rays, however, easily pass through. Credit: ESA/NASA/AVO/Paolo Padovani

However, since there is little understanding of broad emission lines and the different components of BLRs, this method gives rise to some uncertainties off between 200 and 300%. “We are trying to get at more detailed questions about spectral broad-line regions that help us diagnose the black hole mass,” said Brotherton. “People don’t know where these broad emission line regions come from or the nature of this gas.”

In contrast, the team led by Dr. Wang adopted a new type of computer model that considered the dynamics of the gas torus surrounding a SMBH. This torus, they assume, would be made up of discrete clumps of matter that would be tidally disrupted by the black hole, resulting in some gas flowing into it (aka. accreting on it) and some being ejected as outflow.

From this, they found that the emission lines in a BLR are subject to three characteristics – “asymmetry”, “shape” and “shift”. After examining various emissions lines – both symmetrical and asymmetrical – they found that these three characteristics were strongly dependent on how bright the gas clumps were, which they interpreted as being a result of the angle of their motion within the torus. Or as Dr. Brotherton put it:

“What we propose happens is these dusty clumps are moving. Some bang into each other and merge, and change velocity. Maybe they move into the quasar, where the black hole lives. Some of the clumps spin in from the broad-line region. Some get kicked out.”

In the end, their new model suggests that tidally disrupted clumps of matter from a black hole torus may represent the source of the BLR gas. Compared to previous models, the one devised by Dr. Wang and his colleagues establishes a connection between different key processes and components in the vicinity of a SMBH. These include the feeding of the black hole, the source of photoionized gas, and the dusty torus itself.

While this research does not resolve all the mysteries surrounding AGNs, it is an important step towards obtaining accurate mass estimates of SMBHs based on their spectral lines. From these, astronomers could be able to more accurately determine what role these black holes played in the evolution of large galaxies.

The study was made possible thanks with support provided by the National Key Program for Science and Technology Research and Development, and the Key Research Program of Frontier Sciences, both of which are administered by the Chinese Academy of Sciences.

## They asked me what a quasar was. I try to be educational and entertaining.

So a quasar is at the centre of every galaxy? I thought supermassive black holes were at the centre of every galaxy? Does a quasar contain a black hole?

To give a slightly more helpful description: quasars, when originally observed, were objects with really weird emission spectra that no one could explain. Eventually, it was figured out that if you assumed they had a huge redshift, the spectra made sense - but that meant they had to be extremely far away - and with the amount of signal they were emitting, that means they have to be incredibly bright.

My understanding is the current theory is that they are, basically, supermassive black holes doing incredibly violent things to everything in their immediate vicinity. So not just a regular galactic center, but one with a lot of matter near it being ripped apart, spun into an accretion disk, superheated, etc.

A quasar is basically a feeding supermassive black hole, if not much is spiralling in you can only detect them by looking at the tight orbits of nearby stars, if a supermassive black hole has a lot of matter ⟺lling in' like a star for example it is torn apart and orbits ever faster in ever smaller orbits and this causes friction and other heating effects until the matter is so hot it is giving off incredibly intense gamma and X-rays, they are also mostly very very far away so those X-rays are red shifted to visible light and look like stars to us until you do spectral analysis.

I was recently reading about this, and there was a hypothesis that quasars are an early universe phenomenon: a phase through which early galaxies pass, which then settle down to become galaxies more like ours. The quasars we can observe today are extremely far away and therefore very ancient. They represent the distant past.

The Milky Way could have been a quasar, and perhaps at a remove of ten billion light years, it still is one.

Quasars are only found in Active Galactic Nuclei, or AGNs all galaxies contain a black hole, but not all black holes are actively destroying luminous matter, so not all are active.

I study AGN professionally. A few months ago I was talking with a colleague that works on the Illustrious simulation and he mentioned an important distinction: "AGN" is an observational selection, supermassive black holes are the actual physical objects. When we say something is an AGN we mean that it's an object that was selected by some color cut or spectroscopic profile. Quasars are the monster AGN that have a high luminosity and generally completely outshine their host galaxy.

Most (not all!) large galaxies have a super massive black hole in the centre. If this black hole has a bright accretion disc, it's an active galactic nucleus. If it's got a very bright accretion disc, it's a quasar. Usually a quasar is triggered when galaxies merge, stirring up the gas so that it falls into the centre and fuels the accretion disc. When this extra gas gets used up, it settles back down into being an AGN. Once most of the rest gets used up, it becomes a passive galaxy.

Supermassive black holes are believed to be at the center all galaxies, however, a galaxy only hosts a quasar if that supermassive black hole is accreting material (mostly gas), and as it falls in toward the black hole it releases energy. So, the current scientific consensus is, that there is a quasar engine (a supermassive black hole) at the center of a galaxy, but it may or may not be accreting. For example, the Milky Way has a confirmed SMBH, but it isn't accreting.

Interesting fact, the brightest quasars only exist at earlier times in the universe, they do not exist today, and this is because we are seeing these things from so far away. When you look at a quasar, you are looking at an earlier universe. With that said, the Milky Way was probably a quasar ( or at the very least, its SMBH was accreting) earlier in its lifetime. Some think that when the Milky Way undergoes another major merger, such as with the Andromeda galaxy, the SMBH will obtain the fuel to turn on again, but we will be long-gone by the time that happens.

## Supermassive Black Holes Tango in a Distant Quasar

In the center of almost every galaxy lives a Supermassive Black Hole (SMBH), i.e. a BH with mass a million to a billion times the mass of our Sun. Throughout the history of the universe, galaxies collide with each other and form new, bigger galaxies. Naturally, the newly formed galaxy will contain two SMBHs in its center, orbiting around each other, i.e. a Supermassive Black Hole Binary (SMBHB) is formed.

Such systems should be fairly common in galactic nuclei as a result of frequent galaxy mergers. However, we rarely observe them and there is a good reason for this. SMBHBs may spend a large fraction of their lifetime (about ten million years) in very close proximity, with orbital separation less than 1 pc (parsec is a typical distance unit in astronomy, equivalent to 3.26 lightyears). Currently, our telescopes do not have the resolution to detect the individual BHs.

Despite this limitation, we can infer the existence of a SMBHB by identifying the effects of a binary in its environment. One such (indirect) method is to detect periodic changes in the brightness/variability of quasars. This method relies on two assumptions: (1) quasars are thought to be triggered by galaxy mergers, so they may harbor SMBHBs and (2) when we simulate SMBHBs surrounded by gas (which sits in a “circumbinary” disk), as the BHs orbit around each other, they perturb the disk periodically. This leads to periodic infall of gas onto the BHs, which can be translated to periodic changes in the brightness of the binary (e.g., see D’ Orazio et al. 2013).

PG1302-102 was the first discovery of a quasar with periodic variability (over 100 such discoveries followed during the past year). It has a period of 5.2 yr and a mass of

10^9 solar masses. If the observed periodicity is the orbital period of the binary, with simple Newtonian physics, we can calculate that the BHs are separated by 0.01 pc.

### Relativistic Doppler Boost

The authors of this paper came up with an interesting explanation for the periodicity of this quasar. They suggested that this binary doesn’t have to be fed periodically. In fact, periodic accretion of gas would likely lead to a “bursty” periodic light curve, whereas the one observed in PG1302-102 is smooth and sinusoidal.

The authors calculated (again with simple Newtonian physics) that the BHs should orbit with velocities

5% the speed of light. When objects move with relativistic speeds, special relativity can cause interesting effects. For instance, the brightness of the most luminous source (typically the less massive BH in a binary) will appear brighter when it is moving towards us, and dimmer when it’s moving away from us, even if the brightness is constant at the rest-frame of the BHs (relativistic Doppler boost). If the optical emission arises from gas bound to each BHs, and the quasar hosts a unequal mass binary (e.g., if the lighter BH has mass

5% that of the more massive one), then the Doppler effect should dominate the observed brightness. The authors suggested that Doppler boost can explain the optical periodicity and were able to successfully fit the observed data with the Doppler model. Figure 1 shows the light curve of PG1302-102, with grey points corresponding to the optical observations, while the black solid curve shows the best-fit Doppler model.

The Doppler effect will also be imprinted in the variability of the source in other wavelengths, e.g., in the ultraviolet (UV). Just as in optical frequencies, the UV emission also arises from gas bound to the BHs. According to the model, the UV light curve should track the optical, but with amplitude two to three times larger than that of the optical light curve. The relative amplitudes are defined by the ratio of the spectral slopes in the different bands. The authors assumed that the optical and UV continuum of the spectra can be approximated by a simple power-law and measured the UV slope from spectra taken by the Hubble Space Telescope (HST) and the optical slope from a historic spectrum taken in the 1990s, which was presented in the discovery paper. Several photometric observations are available from HST and the Galaxy Evolution Explorer (GALEX) and they were able to confirm that the UV light curve matches the prediction from the Doppler boost model. The near-UV and far-UV observations are shown in Figure 1 with red and blue points, respectively, along with the best-fit Doppler curves, with amplitudes 2.17 and 2.57 times the optical amplitude. The authors noted that since the UV light curve is somewhat sparse, additional follow-up observations are necessary to robustly test the Doppler model.

Figure 1: Optical and UV light curve of PG1302-102. The optical observations are shown with grey, the near-UV with red and the far-UV with blue points. The solid black curve, the dotted red curve, and dotted blue curve show the best fit Doppler curves in optical, near-UV and far-UV respectively. Figure 2 in the paper.

### Summary

Compact (sub-parsec) SMBHBs, which are expected to be strong sources of gravitational radiation, should form frequently following galactic mergers. Despite their expected ubiquity, observational evidence for such sources remains sparse. Recently, a periodic quasar was identified and interpreted as a SMBHB candidate. This paper found evidence for relativistic Doppler boost from the analysis of the optical and UV light curves of the quasar. This effect is caused by the orbital motion of the BHs in a SMBHB and is generally not expected if the quasar hosts a single SMBH. Therefore, it provides strong evidence for the binary nature of the quasar.

## Science Results

A team of astronomers has discovered 83 quasars powered by supermassive black holes (SMBHs) in the distant universe, from an epoch when the universe was less than 10 percent of its present age. This finding was made by using the wide-field camera Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope. The discovery increases the number of black holes known at that epoch considerably, and reveals, for the first time, how common SMBHs are early in the universe’s history. In addition, it provides new insight into the effect of black holes on the physical state of gas in the early universe in its first billion years. Figure 1 shows an example of a discovered SMBH.

Figure 1: Light from one of the most distant quasars known, powered by a SMBH lying 13.05 billion light-years away from Earth. The image was obtained by the Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope. The other objects in the field are mostly stars in our Milky Way, and galaxies seen along the line of sight. (Credit: NAOJ)

Supermassive black holes are found at the centers of galaxies, and have masses millions or even billions of times that of the Sun. While they are prevalent in the present-day universe, it is unclear when they first formed, and how many of them exist in the distant early universe. While distant SMBHs are identified as quasars, which shine as gas accretes onto them (see Figure 2 for an artist impression), previous studies have been sensitive only to the very rare most luminous quasars, and thus the most massive black holes. The new discoveries probe the population of SMBH with masses characteristic of the most common black holes seen in the present-day universe, and thus shed light on their origin.

Figure 2: An artist impression of a quasar. A SMBH sits at the center, and the gravitational energy of material accreting onto the SMBH is released as light. (Credit: Yoshiki Matsuoka)

The research team led by Yoshiki Matsuoka (Ehime University) used data taken with a cutting-edge instrument, Hyper Suprime-Cam (HSC), mounted on the Subaru Telescope of the National Astronomical Observatory of Japan, on the summit of Maunakea in Hawai’i. HSC is particularly powerful in that it has a gigantic field-of-view of 1.77 deg2 (seven times the area of the Full Moon), mounted on one of the largest telescopes in the world. The HSC team is carrying a survey of the sky using 300 nights of telescope time, spread over five years. The team selected distant quasar candidates from the sensitive HSC survey. They then carried out an intensive observational campaign to obtain spectra of those candidates, using the Subaru Telescope, the Gran Telescopio Canarias, and the Gemini telescope. The survey has revealed 83 previously unknown very distant quasars together with the 17 quasars already known in the survey region, Matsuoka and collaborators found that there is roughly one supermassive black hole in each cube a billion light years on a side. Figure 3 shows images of the 100 quasars identified from the HSC data.

Figure 3: The 100 quasars identified from the HSC data. The top seven rows represent the 83 new discoveries, while the bottom two rows represent 17 previously known quasars in the survey area. They appear extremely red due to the cosmic expansion and absorption of light in intergalactic space. All the images were obtained by HSC. (Credit: NAOJ)

The discovered quasars are about 13 billion light-years away from the Earth in other words, we are seeing them as they existed 13 billion years ago. The time elapsed since the Big Bang to that cosmic epoch is only 5 per cent of the present cosmic age (13.8 billion years), and it is remarkable that such massive dense objects were able to form so soon after the Big Bang. The most distant quasar discovered by the team is 13.05 billion light-years away, which is tied for the second most distant SMBH ever discovered.

It is widely accepted that the hydrogen in the universe was once neutral, but was “reionized” (i.e., split into its component protons and electrons) around the epoch when the first generation of stars, galaxies, and SMBHs were born, in the first few hundred million years after the Big Bang. This is a milestone of cosmic history, but it is still not clear what provided the incredible amount of energy required to cause the reionization. A compelling hypothesis suggests that there were many more quasars in the early universe than detected previously, and it is their integrated radiation that reionized the universe. However, the number density measured by the HSC team clearly indicates that this is not the case the number of quasars seen is significantly less than needed to explain the reionization. Reionization was therefore caused by another energy source, most likely numerous galaxies that started to form in the young universe.

The present study was made possible by the world-leading survey ability of Subaru and HSC. The intensive follow-up observations by the Subaru Telescope, Gran Telescopio Canarias, and the Gemini telescope were another key to success. “The quasars we discovered will be an interesting subject for further follow-up observations with current and future facilities.”, said Matsuoka. “We will also learn about the formation and early evolution of SMBHs, by comparing the measured number density and luminosity distribution with predictions from theoretical models.” Based on the results achieved so far, the team is looking ahead to search for yet more distant SMBHs, and to reveal the epoch when the first SMBH appeared in the universe.

The research team consists of 48 astronomers around the world. Matsuoka led the team, while Nobunari Kashikawa (The University of Tokyo), Michael Strauss (Princeton University), Masafusa Onoue (Max Planck Institute for Astronomy), Kazushi Iwasawa (Universitat de Barcelona), and Tomotsugu Goto (National Tsing Hua University) have played key roles in the individual steps of the project. The results of the project are presented in the following five papers (paper [2] in particular).

[1] “Discovery of the First Low-luminosity Quasar at z > 7”, Matsuoka et al., The Astrophysical Journal Letters, 872 (2019), 2
[2] “Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6”, Matsuoka et al. 2018, The Astrophysical Journal, 869 (2018), 150
[3] “Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). IV. Discovery of 41 Quasars and Luminous Galaxies at 5.7 ≤ z ≤ 6.9”, Matsuoka et al., The Astrophysical Journal Supplement Series, 237 (2018), 5
[4] “Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). II. Discovery of 32 quasars and luminous galaxies at 5.7

## Scientists discover the oldest supermassive black hole, and it's too big

Scientists can't explain how the black hole reached this size.

After the universe was created, it took a few million years for the first light to shine across the cosmos. The first stars began forming, and so did ancient galaxies. As the gas and dust at the center of these galaxies began to spiral around their supermassive black holes, they formed the brightest objects in all of the universe — quasars.

Quasars give us a peek into what the universe looked like during its infancy, and scientists are able to look back at these cosmic beasts through telescopic time travel.

A team of researchers recently announced the discovery of the most distant quasar ever observed, dating back to 670 million years after the Big Bang. The quasar was accompanied by the oldest black hole ever observed. But this black hole's extreme age isn't its only notable feature — it is absolutely (super)massive. And scientists also can't explain how it reached its extreme size.

The discovery was announced on Tuesday during the 237th Meeting of the American Astronomical Society, and is detailed in a study accepted for publication in the Astrophysical Journal Letters.

HERE'S THE BACKGROUND — Quasars were discovered in the 1960's. Their name is derived from them being 'quasi-stellar objects,' as a single quasar emits the same amount of light as a trillion stars, all the while occupying an area of space that is smaller than our Solar System.

Scientists believe quasars form when galaxies have an abundant amount of gas and dust surrounding the black holes at their center, which eventually spiral around and form an accretion disc of superheated material that swirls around.

Due to their high energy, quasars often outshine the galaxies that host them.

What's new — Scientists hunt for these ancient beasts as they inform them of the conditions of the early universe, and how galaxies formed and evolved over time. Additionally, quasars can also help scientists better understand the relationship between galaxies and the black holes at their center.

A team of scientists from the University of Arizona was able to detect the most distant quasar ever observed, located 13.03 billion light years away from Earth. This means the quasar existed when the universe was a mere 670 million years old — only five percent of its current age (astronomers believe the universe is 13.8 billion years old).

The quasar, dubbed J0313-1806, is more than ten trillion times as bright as the Sun, and has about one thousand times more energy than the entire Milky Way.

The quasar hosts a supermassive black hole at its center, with the mass of 1.6 billion Suns. Compared to the supermassive black hole at the center of the Milky Way, which is 13.67 million times the mass of the Sun, that's a pretty big boy.

The recent observations also show that the quasar has a stream of super-heated gas flowing out in the form of high-velocity wind from the surroundings of the black hole at a fifth of the speed of light, according to the study.

Here's what we don't know — Scientists are confused by how this supermassive black hole was able to form and grow to such size so early in the universe. In other words, how did it have time to gobble up so much surrounding material in order to reach its massive size?

“Black holes created by the very first massive stars could not have grown this large in only a few hundred million years,” Feige Wang, NASA Hubble fellow at the University of Arizona and lead author of the new paper, said in a statement.

Scientists believe black holes form in the aftermath of the death of a massive star, an explosive supernova, or by feeding off of the first generation of stars that form inside a galaxy. They then continue to grow over time by swallowing material that surrounds them.

The team behind the new study calculated that if the black hole had formed as early as 100 million years after the Big Bang and grew as fast as possible, it would still be around 10,000 solar masses and not the whopping 1.6 billion that it currently boasts.

"This tells you that no matter what you do, the seed of this black hole must have formed by a different mechanism," Xiaohui Fan, associate head of the University of Arizona's department of astronomy, and co-author of the study, said in a statement.

"In this case, one that involves vast quantities of primordial, cold hydrogen gas directly collapsing into a seed black hole."

In addition to being too big for its own good, the black hole is also ingesting the mass equivalent of 25 Suns each year. Scientists believe that supermassive black holes of this size in the early universe are the main reason why ancient galaxies stopped forming stars, with their black holes gobbling up all the gas and other material necessary to birth baby stars.

WHAT'S NEXT — The rather turbulent relationship between black holes and their host galaxies in the early universe gives scientists a rare opportunity to study how galaxies formed and evolved over time, and the effects of their supermassive black holes on their growth.

The researchers are hoping to conduct further observations of this quasar, as well as find more of these quasars in the early universe, following the launch of NASA's James Webb Telescope, currently slated for October 31, 2021.

## Eighty-Three Quasars Spotted in Early Universe

An artist’s impression of a quasar. Image credit: Yoshiki Matsuoka.

Supermassive black holes are some of the most powerful objects in the Universe and are found in the centers of galaxies. They can be millions or even billions of times more massive than the Sun. While they are prevalent today, it is unclear when they first formed, and how many existed in the distant early Universe.

A supermassive black hole becomes visible when gas accretes onto it, causing it to shine as a quasar.

Previous studies have been sensitive only to the very rare, most luminous quasars, and thus the most massive black holes.

“The quasars we discovered will be an interesting subject for further follow-up observations with current and future facilities,” said Dr. Yoshiki Matsuoka, an astronomer at Ehime University, Japan.

“We will also learn about the formation and early evolution of supermassive black holes, by comparing the measured number density and luminosity distribution with predictions from theoretical models.”

“It is remarkable that such massive dense objects were able to form so soon after the Big Bang,” said Princeton University’s Professor Michael Strauss.

“Understanding how black holes can form in the early Universe, and just how common they are, is a challenge for our cosmological models.”

The 100 quasars identified from the Hyper Suprime-Cam data: the top seven rows show the 83 newly discovered quasars while the bottom two rows represent 17 previously known quasars in the survey area they appear extremely red due to the cosmic expansion and absorption of light in intergalactic space. Image credit: National Astronomical Observatory of Japan.

Dr. Matsuoka, Professor Strauss and their colleagues used data taken with the Hyper Suprime-Cam (HSC) instrument on the Subaru Telescope of the National Astronomical Observatory of Japan, which is located on the summit of Maunakea in Hawaii.

The astronomers selected distant quasar candidates from the sensitive HSC survey data.

They then carried out an intensive observational campaign to obtain spectra of those candidates, using three telescopes: the Subaru Telescope the Gran Telescopio Canarias on the island of La Palma in the Canaries, Spain and the Gemini South Telescope in Chile.

The survey revealed 83 previously unknown very distant quasars. The most distant quasar discovered by the team, HSC J124353.93+010038.5, is 13.05 billion light-years away, which is tied for the second most distant supermassive black hole ever discovered.

Together with 17 quasars already known in the survey region, the team found that there is roughly one supermassive black hole per cubic giga-light-year — in other words, if you chunked the Universe into imaginary cubes that are a billion light-years on a side, each would hold one supermassive black hole.

“It is widely accepted that the hydrogen in the Universe was once neutral, but was reionized — split into its component protons and electrons — around the time when the first generation of stars, galaxies and supermassive black holes were born, in the first few hundred million years after the Big Bang,” the researchers said.

“This is a milestone of cosmic history, but we still don’t know what provided the incredible amount of energy required to cause the reionization.”

A compelling hypothesis suggests that there were many more quasars in the early Universe than detected previously, and it is their integrated radiation that reionized the Universe.

“However, the number of quasars we observed shows that this is not the case,” said Dr. Robert Lupton, an astronomer at Princeton University Observatory.

“The number of quasars seen is significantly less than needed to explain the reionization.”

“Reionization was therefore caused by another energy source, most likely numerous galaxies that started to form in the young Universe.”

Yoshiki Matsuoka et al. 2019. Discovery of the First Low-luminosity Quasar at z > 7. ApJL 872, L2 doi: 10.3847/2041-8213/ab0216

Yoshiki Matsuoka et al. 2016. Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). I. Discovery of 15 Quasars and Bright Galaxies at 5.7 < z < 6.9. ApJ 828, 26 doi: 10.3847/0004-637X/828/1/26

Yoshiki Matsuoka et al. 2018. Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). II. Discovery of 32 quasars and luminous galaxies at 5.7 < z ≤ 6.8. Publications of the Astronomical Society of Japan 70 (SP1): S35 doi: 10.1093/pasj/psx046

Yoshiki Matsuoka et al. 2018. Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). IV. Discovery of 41 Quasars and Luminous Galaxies at 5.7 ≤ z ≤ 6.9. ApJS 237, 5 doi: 10.3847/1538-4365/aac724

Yoshiki Matsuoka et al. 2018. Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6. ApJ 869, 150 doi: 10.3847/1538-4357/aaee7a

## Event

Supermassive black hole (SMBH) binaries are inevitably produced during galaxy formation, but observational evidence for them remains elusive. I will discuss the coupled dynamics of a SMBH binary with a circumbinary gas disk, and the expected characteristics of electromagnetic (EM) emission from such a system. In particular, the emission is likely time-variable, and contain unique spectral signatures, which should aid in the identification of SMBH binaries. We have performed hydrodynamical simulations and found that binaries can be fueled efficiently, and that the accretion rates onto the BHs have quasi-periodic modulations. The periodicity pattern depends on the mass ratio, and the strong periodic emission persists all the way to the merger. This may be used to identify unique counterparts of gravitational wave sources expected to be detected by Pulsar Timing Arrays and by LISA, and to discover wider binary SMBHs in time-domain EM surveys. We have identified a handful of quasars with periodic
optical variability on the timescale of O(year). I will comment on the interpretation of these quasars as SMBH binary candidates, and on the possibility of seeing an analogous "X-ray chirp" during the late-stage inspiral a LISA binary.