A giant black hole a long, long way away

December 4, 2023   Issue #651

Subscribers glow brightly at high energies 

Astro Tidbit

A brief synopsis of some interesting astronomy/science news

We know that big black holes form early on in the Universe, and their galaxies grow around them at the same time. Their growths are related, in fact, with some aspects of the galaxy scaling with the mass of the black hole. To help understand how this happens, we need observations of these supermassive black holes as early on in the universal timeline as possible, which means looking ones that are very, very far away (the longer it takes the light to reach us, the farther back in time we see).

So this news is pretty exciting: Astronomers have detected the most distant black hole ever seen in X-rays.

The galaxy is called UHZ1 (which I expect is short for Ultra High Z 1, where z means redshift, and the 1 because it’s the first one seen by this team), and its light has been traveling to us for a stunning 13.3 billion years; we see this galaxy as it was when the Universe itself was under 500 million years old (it has a z = 10.1, for those keeping score at home).

The galaxy is extremely faint, and in fact would be invisible if it wasn’t for a fortunate happenstance: From our vantage point, we see it behind a massive galaxy cluster called Abell 2744. That cluster (about 3.5 billion light-years away) has a huge gravity well that acts like a lens, magnifying and amplifying the light from the more distant background galaxy, making it possible to detect. This is called gravitational lensing.

The distant galaxy was seen in JWST images and IDed as being far away, so the wonderful Chandra X-Ray Observatory swung into action [link to research paper]. It took deep images of the area, and spotted high-energy light coming from UHZ1. As matter falls into a black hole, it spirals in and creates a flat accretion disk. That material heats up to supernatural temperatures, so hot it glows in X-rays. It was those powerful photons Chandra saw.

The X-rays reveal its presence, but can also be used to determine how big the black hole is. Astronomers found it’s between 10 and 100 million times the mass of the Sun, which is a decently portly object, especially for such a young ‘un (the Milky Way’s central supermassive black hole is about 4 million solar masses; admittedly a lightweight for galaxies our size, but still).

The fact that it’s so massive so early is very interesting. A big question about these beasts is whether they are born big and grow rapidly, or start off small and grow really fast. Given how big this one is so young, it’s far more likely the monster in the middle of UHZ1 was born beefy. It likely formed from gas streaming to the center of the galaxy, a flow so fierce it collapsed directly into a black hole of appreciable size — what’s a called a seed. It started growing from there.

A lot of gas is still falling into, too. A lot. The amount of light it’s blasting out is roughly a trillion times the Sun’s energy. A trillion. That’s brighter than our entire Milky Way galaxy! And the galaxy host for the black hole isn’t terribly big, probably about 50 million times the mass of the Sun, which means the black hole and the galaxy are roughly the same mass. That’s incredible; in the Universe today that ratio is far higher; galaxies tend to be about a thousand times their central black hole mass. So the black hole in the heart of UHZ1 is a major overachiever [link to research paper].

Usually, when we look to the distant Universe, the objects we find there tend to be the biggest and brightest. This is a selection effect, a kind of bias, because those are the easiest objects to see. On the other hand, the only reason we see this one at all is that its light was amplified by the cluster, so these kinds of situations (with outsized black holes) may be more common. One way to find out is to keep looking at clusters with JWST, find very distant galaxies, and then check on ‘em with Chandra.

The galaxy/black hole symbiosis is still a big open question in cosmology. How fast do they each grow? Does one form first, or do they come into being together? How does one affect the other? And how does all this lead to the situation we see in the later Universe?

Right now we still have way more questions than answers. But we’re also amassing evidence that will help lower that ratio.

News Roundup

Who can keep up with everything these days?

• Dinkinesh’s weird little moon gets a name! Dinkinesh is the wee asteroid the Lucy mission zoomed past on November 1, taking images as a sort of practice run before it gets to Jupiter’s orbit and starts taking the measure of the Trojan asteroids that share its orbit. When it got close to Dinkinesh it saw that the asteroid has a moon, and in a surprise turn the moon is a contact binary! That was very cool. And now the International Astronomical Union (the official keeper of celestial names) has confirmed the moon is now named Selam, which means “peace” in Amharic, an Ethiopian language. Lucy is named after the fossil Australopithicus afaransis skeleton found in Ethiopia, and Dinkinesh is the name of the fossil in Amharic. Selam is another A. afarensis that was found, sometimes called Lucy’s baby, so the name is perfect! I’m a big fan of how all these objects have been named, so I find all this quite delightful.

• Some surprising news related to climate change: E-scooters and mopeds are having a huge impact on fossil fuel use, displacing four times as much demand for dirty fuels than electric cars globally! This is primarily because they’re in huge demand in China, which isn’t surprising. They’re extremely useful in dense urban areas, where most rides are short and use far less power per kilometer than much heavier cars. It’s something to consider. The US is massively designed to support cars, so it’s hard to say how much uptake smaller vehicles would get here, but I bet for a lot of folks they’d make a lot of sense.

Et alia

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