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Astronomers have found the most distant quasar ever, and like a handful of others found at this distance, it presents a huge problem (literally): The black hole that powers it has been far too large for how long it’s been around. .
The quasar is named after its coordinates on the sky, J031343.84−180636.4 (let’s call it J0313 for short). It was found in a survey of the sky using Pan-STARRS, the Panoramic Telescope and Rapid Response System, a relatively modest 1.8-meter telescope that nonetheless takes very deep images of the sky, monitoring the sky. using different filters to get color information about objects. Quasars that are very far away tend to be bright in the red but emit very little light at blue wavelengths, making them a bit easier to spot.
Once J0313 was identified as a candidate, the much larger Magellan and Gemini telescopes took on a spectrum confirming the immense distance: the light we see from this object has traveled over 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 a active galaxy. Every large galaxy has a supermassive black hole in its core, and in some cases, that black hole actively feeds on itself, engulfing gas, dust, and stars around it. This material forms a huge, flat disc around it, which gets extremely hot. It shines so bright it can easily outshine the stars all over the rest of the galaxy combined!
To make matter more intense (again, literally), the magnetic field in the disk coils into two vortices, like tornadoes, which pull matter from the disk and project it just outside the black hole. If these beams are pointed more or less in our direction, they make the galaxy even brighter. This is what makes the galaxy a quasar.
Considering the brightness of J0313 seen and its distance, astronomers measure its total brightness – how much energy it gives off – as 36 thousand billion times the sun.
It’s … brilliant. It’s almost three thousand times brighter than our own Milky Way. Oof.
So what about the supermassive black hole that is fueling all of this? In the case of J0313, the deep spectra taken by Magellan reveal the mass of the black hole. As the matter swirls around the disk, some of the matter moves away from us, so its light shifts toward red, and another toward us, which turns blue. The amount of these color spots can be used to determine the mass of the black hole, and the number they got is overwhelming: 1.6 billion times the mass of the Sun.
We know of many black holes with this mass, and some even larger ones. But these have had billions of years to reach this size. At best, the one in J0313 is 670 million years old, and actually a little younger. How did it get to such huge proportions so quickly?
It is an ongoing problem in cosmology. We’ve seen other quasars around this distance away, and they also have huge black holes, bigger than we realize in the short time (galactically speaking) they’ve been.
The problem is, black holes can only eat matter so quickly. Matter tends to form these discs around them, and the disc is so hot that the radiation it projects hits the material falling towards the black hole and blows it out. For a given black hole mass, the speed at which it can eat is balanced by the radiation it emits, called the Eddington limit. Eat too fast and it cuts off its own food supply.
This in turn means that it is very difficult to get a black hole with over a billion solar masses so quickly. However, there are several ideas to work around this problem. Maybe smaller black holes are forming (with thousands or hundreds of thousands of times the mass of the Sun) – seed black holes – and these are growing rapidly and coalescing into the nascent galaxy. It can help a lot, even if they still have to grow very quickly.
How this process works is not entirely clear, however. We don’t know many quasars at this distance (it’s a big sky, there aren’t many that far, and it can be difficult to pick them out in a crowded area), but the fact that the handful see us, they all have huge central black holes, which means they’re growing sort of. I will note that there may be quasars with lower mass black holes and less powerful emissions, but they are weaker and more difficult to find. And finding them would just mean that lower mass black holes of course can form, but the problem remains how the truly monstrous holes do.
The galaxy itself surrounding the black hole is apparently producing stars at a rate two hundred times greater than what the Milky Way does, making it what we call a star galaxy. It may be related to the mass of the black hole; plenty of material to make stars and feed a hungry beast in its heart.
Understanding all of this is important. On the one hand, we know that galaxies and their black holes grow together, so understanding one means understanding the other. But it also tells us about the conditions under which the Universe was extremely young and still starting to take off. On top of that, the light from these distant objects passes through objects closer to us on its way here, and the way they affect that light tells us even more about the not-so-distant Universe.
Now that we know it exists, J0313 will be a prime target for many follow-up observations to find out more. These quasars are a big problem, and the more we know about them, the more likely we will find the solution.
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