The Fastest Growing Supermassive Black Hole in 9 Billion Years

Astronomers from The Australian National University have led an international collaboration to discover the fastest-growing supermassive black hole from the last nine billion years of the Universe’s history. 

The energetic supermassive black hole, known as a quasar, is consuming an enormous amount of material - the equivalent of swallowing the mass of Earth on a per-second basis. This powers the behemoth to shine 7,000 times brighter than all of the Milky Way’s stars combined. And whilst it is located at a redshift distance of z = 0.83 (about 11.4 billion light-years away), it’s bright enough for backyard astronomers to even capture it with their home telescopes. 

Supermassive black holes reside in the centre of most galaxies, and unlike their stellar-mass smaller cousins - which have masses in the range of five - 150 times that of the Sun, these gargantuan objects have masses in the millions or billions of times that of our parent star. 

By using spectroscopic data (where the light from astrophysical sources is split into different wavelengths, and spectrum information is analysed) the team observed several emission lines from the broad line region of the quasar, which was then used to find the mass of this particular object, named SMSS J114447.77-430859.3 (or J1144 for short). What they found is that J1144 weighs in at three billion times solar masses, and is about 500 times larger than the supermassive black hole in the centre of our Milky Way Galaxy (known as Sgr A*).

Lead researcher Dr Christopher Onken and his co-authors describe it as a "very large, unexpected needle in the haystack".  

"Astronomers have been hunting for objects like this for more than 50 years. They have found thousands of fainter ones, but this astonishingly bright one had slipped through unnoticed," Dr Onken said.  

What makes J1144 even more interesting is that it raises questions about how it became so massive, so early on in the Universe’s history. As with other supermassive black holes and quasars observed at great distances (and thus, even further back in the Universe’s history) - astronomers want to know how they could form so large when the evolution timeframes of these objects cannot be accounted for. 

For example, one model says that supermassive black holes are formed when smaller stellar-mass black holes merge with each other, getting bigger in the process as they consume and collide with other black holes. But this model requires that massive stars live out their lives first, undergo their supernovae events, merge with another black hole, then go on and merge with more black holes, with this process continuing onwards until you get to the billions of solar mass ranges. 

The other model is that supermassive black holes formed from collapsing clouds of massive clouds of material, which might go to explain how they got so big so quickly, but unfortunately runs into problems when we compare this to the data that has been observed so far - such as the event and population statistics of merging black hole binaries as observed by the gravitational wave detectors LIGO, VIRGO and KAGARA. 

When comparing J1144 with other quasars of comparable size, astronomers started to question why others like it stopped growing so quickly billions of years ago. 

"Now we want to know why this one is different - did something catastrophic happen? Perhaps two big galaxies crashed into each other, funnelling a whole lot of material onto the black hole to feed it," Dr Onken said. 

Co-author Associate Professor Christian Wolf said: "This black hole is such an outlier that while you should never say never, I don't believe we will find another one like this. 

"We are fairly confident this record will not be broken. We have essentially run out of sky where objects like this could be hiding."   

Quasars belong to a family of objects known as Active Galactic Nuclei (AGN) which are supermassive black holes observed in a highly active state (i.e., they are energetic due to consuming a large amount of material when we observe them). They can also have a variety of names, depending on which angle we observe these objects from, and in which part of the electromagnetic spectrum.

When they were first discovered, quasars confused astronomers, as they were not really sure what they were looking at. These tiny, star-like points of light were giving off enormous amounts of energy (in radio and optical frequencies) - more so than any individual stellar object could on its own. 

Deepening the mystery, when scientists observed their spectrum and the way their light was red-shifted (stretched due to the expanding Universe), they found that these objects were extremely distant from us. So, not only were they bright, but they were bright from a distance - making them extremely powerful objects. Only something like a supermassive black hole could be causing it, they determined.  

The energy of quasars and other AGN doesn’t come directly from the supermassive black hole itself - because no information can ever leave a black hole of any size. Instead, this output is generated by materials like stars and gas that are pulled into an accretion disc around the supermassive black hole, being subjected to immense stresses and frictional forces. Additionally, some of these objects have powerful jets that we can also observe as well.

To catch the light and spectrum from J1144, the team of astronomers used the 1.3-metre telescope at the Siding Springs Observatory near Coonabarabran (in the north, central NSW) as part of the SkyMapper Southern Sky Survey. This collaborative survey (which features seven Australian universities and the Australian Astronomical Observatory) is on a mission to create a deep, multi-epoch, multi-colour digital survey of the entire southern sky. 

But some quasars are bright enough for even backyard astronomers to photograph - even from bright city locations if the right equipment is available. And given that the visual magnitude of J1144 from Earth is about 14.5 (a measure of how bright an object is) - then this should be within the reach of the keen astrophotographer. Thanks to its extreme brightness, the object is only slightly dimmer than Pluto.

Quasar light is so bright, that backyard astronomers’ can even take its spectrum if the sky conditions are good and the right equipment is at hand. Australian astrophotographer, Andy Casely has previously photographed and captured the spectra of the closest, and brightest quasar to Earth, QSO 3C 273.