Some Quasars Shine With the Light of Over a Trillion Stars

Universe Today | 10/16/2019 | Staff
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Quasars are some of the brightest objects in the Universe. The brightest ones are so luminous they outshine a trillion stars. But why? And what does their brightness tell us about the galaxies that host them?

To try to answer that question, a group of astronomers took another look at 28 of the brightest and nearest quasars. But to understand their work, we have to back track a little, starting with supermassive black holes.

Hole - SMBH - Hole - Masses - Billions

A supermassive black hole (SMBH) is a black hole with more than a million solar masses. They can be much larger than that, too; up to billions of solar masses. One of these entities resides at the center of most galaxies, excluding dwarf galaxies and the like.

They’re the result of the gravitational collapse of a massive star, and they occupy a spheroidal chunk of space from which nothing, not even light, can escape.

AGN - Hole - Matter - Torus - Gas

In an AGN, the black hole is actively accreting matter, forming a torus of gas that heats up. As it does so, the gas emits electromagnetic radiation, which we can see. AGNs can emit radiation all across the electromagnetic spectrum.

There are sub-classes of AGNs, and a new study focused on one of those sub-classes called quasars. A quasar is the most powerful type of AGN, and they can shine with the light of a trillion Suns. But some of these quasars are hidden behind their own torus, which blocks our line of sight. In studies of quasars, these ones are ignored or omitted, because they’re difficult to see.

Problem - Population - Quasars - Something - Questions

But that creates a problem, because omitting them from the population of quasars means we might be missing something. It also means that one of the central questions around quasars might not be addressed properly.

The question is really multi-pronged: are these extremely bright AGN powered by moderate accretion onto...
(Excerpt) Read more at: Universe Today
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