At the core of every galaxy lies a supermassive black hole (SMBH). These behemoths are many times the size of ordinary black holes. And unlike your garden-variety stellar-mass black hole, supermassive black holes didn’t form from a collapsing star; rather, they formed.... well, we actually don’t know how they formed. But we do know just how big they are. An ordinary black hole can have about five to several tens of times the mass of the Sun (solar masses), where our own galaxy’s SMBH has about four million solar masses.

While we don’t yet know the mechanism by which SMBHs form, the prevailing thought is that they formed (relatively) small, with “only” 100 to 100,000 solar masses. They would then have gained mass over time as they gobbled up matter, ultimately growing to become the giants we see today.

A new SMBH has now been discovered with about twelve billion solar masses. By itself, that’s not unprecedented; others have been discovered with roughly the same mass. What’s astounding about the new discovery is the extreme distance of the SMBH—about 12.8 billion light-years from Earth—and hence, how quickly after the Big Bang it formed.

A long time ago...

Because it’s so far away, light generated by the SMBH takes a long time to get here—so long that the light we’re seeing now was emitted when the Universe was only 875 million years old, six percent of its current age of 13.8 billion years. We’re seeing the black hole as it was then. The new SMBH is a quasar, an extremely luminous kind of SMBH. The idea of black holes emitting light may seem counter-intuitive, but the light doesn’t come from the black hole itself; rather, it’s produced by friction in the black hole’s accretion disk, a disk of infalling matter. The more matter in the disk, the more friction and thus more light is produced. Jets of energetic particles emerging from the black hole's poles also generate light.

It’s the most massive SMBH discovered that far in the past, which is one of the reasons the discovery is so surprising. It takes time for black holes to get so big, usually quite a bit of time. And since this one had already grown to its full twelve billion solar mass grandeur within the first 875 million years of the Universe’s history, it must have been consuming matter at an astounding rate.

The researchers calculate that it must have been taking in matter at the maximum rate, its Eddington limit. The Eddington limit exists because the faster a black hole gobbles up matter, the more friction—and thus more light— is produced in the accretion disk. The extra light radiates outward, putting pressure on the infalling matter, slowing it down. (Counter-intuitive as it may seem, light does actually put pressure on objects; with enough light, this can amount to a significant force). As the black hole’s consumption rate increases, the amount of radiation increases, which in turn slows down the consumption rate. And when it reaches the Eddington limit, the radiation pressure prevents the rate from increasing any further.

But if the SMBH was consuming at its Eddington limit for its entire existence, accretion should have stopped. It was thought that the intense radiation produced from such a massive object radiating at its Eddington limit—releasing the maximum amount of radiation it can produce that way—should be enough to drive away any nearby matter. Clearly that hasn’t happened.

...In a (massive) galaxy far, far away

From studying nearby galaxies, researchers have learned that there’s a correlation between an SMBH’s mass and its host galaxy’s mass. Typically, an SMBH makes up a small percentage of its host galaxy’s mass, ranging from about 0.14 percent to 0.5 percent. If this relationship holds true in the early Universe, the new SMBH’s host galaxy should have a staggering four to nine trillion solar masses in stars. (To say nothing of its dark matter component, which is by far the most massive part of every galaxy). Galaxies of this mass are not unheard of, as they exist in the present Universe. But if the galaxy does indeed exist in the predicted mass range, it will be the first discovered in that era.

Studying such a massive galaxy would provide clues about how galaxies grew in the early Universe. One of the important unknown factors in galaxy formation is the role played by the galaxy’s SMBH. Why is there a correlation between the black hole’s mass and the galaxy’s? What kind of relationship exists between the SMBH’s accretion and the formation of stars?

Such questions regarding an SMBH’s role in its host galaxy have been keeping researchers busy for some time—while there are some compelling models, there's been no consensus on which one is right. By studying the new SMBH and its host galaxy, we could begin to find those answers. "This quasar is a unique laboratory to study the way that a quasar's black hole and host galaxy co-evolve," said Yuri Beletsky, one of the paper's authors. "Our findings indicate that in the early Universe, quasar black holes probably grew faster than their host galaxies, although more research is needed to confirm this idea."

To boldly go

The quasar’s light can also be used to learn about the early Universe in other ways. For one thing, its extreme brightness will allow researchers to probe the intergalactic medium like never before.

The intergalactic medium is a thin distribution of gas and dust between galaxies, containing hydrogen, helium, and various metals (in astrophysical terms, all the elements above helium are known as ‘metals’). The light from the quasar has to pass through a lot of space before it gets here, including the intergalactic medium in its neighborhood.

When light passes through a gas, some wavelengths of light are better at penetrating the gas than the others, while some elements block specific wavelengths. So by studying the spectrum from an object and seeing which wavelengths are missing from the spectrum, researchers can learn about the contents of the gas. However, the process is complicated, especially over such great distances. With dimmer light, it’s harder to distinguish these gaps, or lines, in the spectrum. The quasar’s brightness, therefore, will provide a much clearer measurement of the intergalactic medium.

And since the metals in the intergalactic medium were produced by fusion in the cores of stars, better measurements of these elements there can help researchers learn about the star formation processes going on in the early Universe.

The next generation of telescopes will reveal more. Not only will they be able to study this SMBH further, they will also likely be able to discover more massive objects like this one in the very distant early Universe.

Nature, 2015. DOI: DOI: 10.1038/nature14241 (About DOIs)