Astronomers have found the most distant quasar seen so far, and, like a handful of others found at this distance, it poses a huge (literal) problem: The black hole it powers is far too big for how long it has existed.
The quasar is named for its coordinates in the sky, J031343.84-180636.4 (let’s call it J0313 for short). It was found in a survey of the sky with Pan-STARRS, the Panoramic Survey Telescope and Rapid Response System, a relatively modest 1.8-meter telescope that nevertheless takes very deep images of the sky, examining the sky using different filters to get color information on objects. Very distant quasars are usually bright in red, but emit very little light at blue wavelengths, making them a little easier to spot.
Once J0313 was identified as a candidate, the much larger Magellan and Gemini telescopes took a spectrum that confirmed the immense distance: the light we see from this object has traveled more than 13 billion years to get here, which means we see it as it was about 670 million years after the big bang itself!
And that’s a problem. A quasar is an object that we call one active galaxy. Every major galaxy has a supermassive black hole at its core, and in some cases that black hole is actively feeding, consuming gas and dust and stars around it. This material forms a huge flat disc around it, which becomes extremely hot. It glows so brightly that it can easily outshine the stars all over the rest of the galaxy!
To make matter more intense (again, literally), the magnetic field in the disc winds up in double eddies, like tornadoes, that pull matter off the disc and blow it away from just outside the black hole. When those rays are directed more or less in our direction, they make the galaxy even brighter. That makes the galaxy a quasar.
Given the brightness of J0313 and its distance, the astronomers measure the total brightness – how much energy it gives off – as 36 trillion times the sun.
That’s … clear. It is near three thousand times lighter than our own Milky Way. Oof.
So what about the supermassive black hole powering all of this? In the case of J0313, Magellan’s deep spectra reveal the mass of the black hole. As the matter swirls around the disk, some of the matter is diverted away from us, so the light is shifted to the red, and something towards us, which is shifted blue. The amount of this color smear can be used to determine the mass of the black hole, and the number they have is crushing: 1.6 billion times the mass of the sun.
We know many black holes with that mass, and some even bigger. But they have had billions of years to grow to that size. The one in J0313 is 670 million years old at best, and actually slightly less. How did it grow to such enormous proportions so quickly?
This is an ongoing problem in cosmology. We’ve seen other quasars about this distance, and they also have immense black holes in them, bigger than we think they could be in the short time (galactically speaking) they’ve been there.
The problem is, black holes can only eat material that quickly. Matter tends to form those discs around them, and the disc is so hot that the radiation that blows out hits the material that falls towards the black hole and blows it away. For a given massive black hole, the rate at which it can eat is balanced by the radiation it emits, the so-called Eddington Limit. Eat too fast, and it cuts off its own food supply.
That in turn means that it is very difficult to get a black hole with more than a billion solar masses so quickly. However, there are several ideas for getting around this. Smaller black holes (thousands or hundreds of thousands of times the mass of the Sun) – black holes from seed – may be forming and grow rapidly and merge into the nascent galaxy. That can help a lot, although they still have to grow very quickly.
However, it is not entirely clear how this process works. We don’t know many quasars this distance (it’s a big sky, there aren’t many that far away, and it can be difficult to get them out of a crowded area), but the fact that out of the handful of us. all have huge central black holes, which means they are growing somewhere. I will note that there may be quasars with lower mass, less powerful emission black holes, but they are weaker and more difficult to find. And finding it would just point out that certainly lower mass black holes can form, but still leaves the problem of how the really monstrous holes fare.
The galaxy itself around the black hole apparently spins stars several hundred times faster than the Milky Way, making what we consider a starburst galaxy. That may be related to the mass of the black hole; lots of stuff in it to make stars and feed a hungry beast at its core.
Understanding all of this is important. To begin with, we know that galaxies and their black holes grow together, so understanding one means understanding another. But this also informs us of what the conditions were like when the Universe was extremely young and still emerging. In addition, the light from these distant objects on its way here passes objects closer to us, and how they affect that light tells us even more about the not-so-distant Universe.
Now that we know it’s there, J0313 will be a prime target for many follow-up sightings to learn more about it. These quasars are a big problem, and the more we know about them, the more likely we are to find the solution.