It is famously hard to see black holes.

I mean, they’re called “black” for a reason. Despite the fact that light can  travel at the fastest possible speed through the universe, even it can’t escape a black hole’s gravitational  clutches if it gets too close.

And yet … not all black holes  are shrouded in darkness. Some of them even manage to  outshine an entire galaxy. In fact, there’s one black hole that’s  the size of an entire solar system, and powers the brightest  object in the known universe. [♪INTRO] That brightest object is what  astronomers call a quasar.

And quasars are a type of active galactic nucleus. Basically, it’s the core of a  galaxy that’s home to not just any supermassive black hole, but one  that is actively devouring a bunch of gas, dust, and so on…even if it  has to tear a whole star asunder. And the way astronomers can tell  whether or not a black hole is active is by looking at how bright  it is.

Or, rather, how bright all the stuff swirling /around/  the black hole has gotten. Because as matter falls closer and  closer to the black hole, it heats up. And when things get hot, they glow.

Some of that light gets beamed  directly into our telescopes, and some of it gets absorbed  by even more matter that’s a bit further away from the black hole, which makes it heat up and start glowing, too. So all together, an active  galactic nucleus will shine basically all across the electromagnetic spectrum. One rule of thumb is if you’ve  got a galactic core that’s 100 times brighter than the  rest of the galaxy combined, you’re dealing with an active galaxy  and its active galactic nucleus.

And astronomers love these things, in large part due to their brightness. Or, technically, their luminosity. Because despite sounding like  synonyms, those are different things.

Luminosity is the amount of  energy an object puts out. And brightness is how…well… bright the object appears to an observer given how far away it is. Because space is just so darn big,  you could have an active galaxy that’s way more luminous than a  run-of-the-mill galaxy, but it’s not brighter in your image because  it’s a lot further away from you.

That being said, astronomers  do have a way to report brightness that tries to  compensate for different distances. And it’s easier to say “bright” than “luminous”. So we’re going to just stick with that.

Anyway, the fact that active  galactic nuclei like quasars are so much brighter than non-active  galaxies means they’re easier to see. And that’s especially handy  when you’re looking farther and farther away, where  signals grow dimmer and dimmer. It’s why almost all the galaxies  that have tried to claim the title of “most distant galaxy” are quasars.

And together, they’re helping astronomers learn about the universe’s toddler years. But just because we can see them,  doesn’t mean we understand them. For example, we still don’t know how  quasars can get so big so quickly.

So, we have to study them  to figure this stuff out. But the problem is, even though  they’re often the brightest things in their cosmic neighborhoods, quasars  can be weirdly hard to find. And that’s largely because  they don’t look like massive galactic cores.

They often  look like plain ol’ stars. In fact, that’s where they get their name. Quasar is short for “quasi-stellar radio sources”.

But that’s not to say we can’t  tell quasars and stars apart. We just have to try a little harder. This SciShow video is supported by Bombas!

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And you can be a part of that today! New customers get 20% off their first purchase at bombas.com/SCISHOW using code SCISHOW at checkout. Enter SMSS J052915.80–435152.0.  It’s the brightest quasar ever.

This record-setter was first “spotted”  by a telescope survey mission in the 80s, but astronomers didn’t  know it was a quasar until 2023! In all likelihood, that was  due to an algorithm that astronomers were using to  sort through the huge amounts of data that the telescope was  collecting night after night. In other words, the survey  didn’t have a specific target.

It was just staring at a  huge swatch of the sky that contains a bunch of different,  potentially interesting objects. And astronomers rely on software to help  filter out all the stuff that isn’t. So the computer probably went something like “Well this can’t possibly be  a quasar, it’s too bright!

It must be a foreground star. So don’t bother.” But thanks to a second look  with a different telescope, one team of astronomers managed  to uncover its true identity. It wasn’t some random photobombing  star in the Milky Way.

It was a quasar located at a redshift of 3.962. Now, if you’re not an astronomer,  that doesn’t really mean anything. But redshift is a property that reveals  how far away other galaxies are.

Especially galaxies that  are really really far away. You can kinda think of  redshift as the Doppler effect, but for light instead of sound. If an object like a galaxy is moving away from us, that motion stretches out the light  waves heading in our direction, so they look redder than they otherwise would.

And since the universe is not just getting bigger, but getting bigger faster over  time, the further away a galaxy is, the /more/ its light gets redshifted, and the higher that redshift number. So if astronomers measured  a redshift of 3.962 for our quasar friend here, how  far away does that make it? And since it takes time for  light to traverse the universe, how old is our picture of this thing?

Well…we’re not really sure. To translate a redshift into,  say, light years, we have to make a few assumptions, like how  fast the universe is expanding. And unfortunately, astronomers have… let’s say some conflicting…measurements for that.

But very roughly, we’re seeing this quasar as it looked about 12.8 billion years ago, and when the universe was about 860 million years old. That actually puts it a lot closer to us than other unusually large quasars. Given that distance, it means that  as dim as it appears in the sky, it’s actually about 500 trillion  times brighter than the Sun, by which I mean, luminous, nothing else in the known universe is that bright.

And to pump out all that light,  it requires an active supermassive black hole that’s about 17  billion times the mass of our Sun. Which is not the most massive  black hole we’ve ever seen, but it’s still doing pretty well for itself. Because it also appears to be the fastest growing black hole in the universe.

Every year, it consumes somewhere between 280 to 490 Sun’s worth of matter. You could average that out and  say it eats about one Sun a day. Which also means it’s probably  eating off the largest known plate in the universe…if we’re calling the  accretion disk a “plate”, now.

That is…a lot of superlatives. Astronomers may eventually uncover another object that’s even brighter. Perhaps it’s another mis-identified quasar just chilling out in some survey data.

But in the meantime, they  can try to work out exactly how these things are made in the first place. So you might say the future of quasar research is looking pretty luminous…by which I mean bright. [♪OUTRO]