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Black holes are already pretty extreme, but some stand out among their peers, driving cosmic engines that outshines the rest of the galaxy and even serving as birth control for stars!

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[♪ INTRO].

Black holes are one of the most extremely dense objects in the known universe, but even they can level up. Within the hearts of the largest galaxies, you can find black holes with masses exceeding a billion times that of our Sun.

And a fraction of these has superpowers all their own, like driving a cosmic engine that outshines the rest of the galaxy and even serving as birth control for stars. In the late 1950s, astronomers began matching point-like radio signals in the night sky with optical signals coming from the same spot. That visible light was also a point, like all the stars we’re used to seeing.

But when astronomers split up the light into its different colors, they noticed that the combination of colors did not follow the pattern for any known type of star. So astronomers called them QSOs, quasi-stellar objects. They’re commonly known today as quasars, short for quasi-stellar radio sources.

Well it turned out the light looked different because the quasars were far away…they were very far away. Far enough that the universe’s expansion could noticeably stretch out the light waves on their way to us. The amount of stretching could tell us these quasars were billions of light-years away.

So, in order to be visible to us, a quasar would have to be super bright, up to thousands of times brighter than all of the starlight in an entire galaxy. An impressive feat considering that some of them are as small as a single solar system. Scientists did eventually learn how all of this is possible.

A quasar is a type of active galactic nucleus, or AGN. To make one, you need a supermassive black hole at the heart of a galaxy that is actively slurping up matter around it. All that matter gets heated up through friction as it spirals down into the black hole, becoming so hot it starts to visibly glow.

But because that black hole engine is so powerful, the effect is a bit more intense than what you see happening in the coils of your space heater. The brightest quasar we’ve found so far is as bright as 600 trillion Suns. But being bright isn’t good enough for these guys.

Between 20 and 50 percent of AGNs produce a kind of space wind astronomers call “outflow,” where light and other particles are thrust out in all directions from the quasar at the center of the galaxy. The next question was how much of an influence this outflowing material could have on the rest of the galaxy. Like, could it redistribute energy or matter so much it prevented a bunch of baby stars from forming, or actually make a bunch of new baby stars?

Astronomers have been looking for an answer for decades and just a few years ago, the jury was still out. A series of papers published in The Astrophysical Journal: Supplement Series back in 2020 has thrown some additional data into the ring, focusing on a narrow range of light we get from quasars: high-energy UV wavelengths. These wavelengths are formed after the outflow smashes into the matter around the galaxy, raising temperatures billions of degrees.

That means a lot of the light these outflows emit is in the ultraviolet and X-ray part of the electromagnetic spectrum. The team behind these papers wanted to investigate both how fast these outflows were moving through the galaxy and how far they extended from the galactic center to determine if an AGN had an effect on its galaxy. To get those measurements, they collected the spectra of ten different quasars across several years, using the Hubble Space Telescope.

Spectra are like chemical fingerprints. Dips in the signal at different wavelengths of light, called “troughs,” correspond to different elements flowing toward us and away from the AGN. Hubble provided clear signals from quasars up to 9.4 billion light-years away.

And the super high-energy UV part of the spectrum has way more troughs to analyze than longer UV wavelengths, while also covering about 90 percent of the matter in the outflows. Across seven papers, the team reported a number of results. In one case, studying 13 outflows from four quasars, they found that nine of those outflows had extended anywhere from 326 to 6,523 light-years beyond their galactic centers.

Although the outflow is smaller than what a galaxy measures across, they are still bigger than what quasar models previously predicted. In another paper, they report on the same outflow, but measured twice about three years apart. They found that the outflow accelerated, up to around 21,000 kilometers per second.

That’s around 74 million kilometers per hour! And they conclude that this new data suggests a “large fraction” of outflows produce AGN feedback, which means that AGNs influence how fast stars form in their galaxies. In this case, the gas that would have otherwise been cool enough to collapse down into baby stars suddenly gets too hot to handle, and has to cool down all over again for them to form.

But the outflows can also push matter away. One of the astronomers even said it's equivalent to hundreds of our Suns in gas each year, which could literally starve stellar nurseries of the material they need. But the debate on outflows and feedback isn’t settled completely.

Ten quasars is a tiny sample size, especially compared to the millions we’ve cataloged. New telescopes, like the James Webb Space Telescope, will provide even better optics that will allow astronomers to view these distant beads of light in even better detail. Thanks for watching this episode of SciShow Space!

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