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May 28, 2015

A quasar is an impressive contradiction. It’s among the brightest objects in the universe, yet it’s powered by one of the darkest — a supermassive black hole.

The first quasars were discovered in the 1960s. They produced enormous amounts of radio energy, but looked like ordinary stars. They were called quasi-stellar objects — a lengthy moniker that soon was shortened to “quasar.”

Later observations showed that these objects are billions of light-years away, so they can’t be individual stars. And later still, it was found that they’re embedded in the hearts of galaxies. And they can change brightness in a matter of hours, which means that they’re not all that big.

From those observations, theorists developed the likely explanation: a supermassive black hole swallowing enormous amounts of gas and dust. As it spirals inward, this material forms a disk around the black hole. The disk is heated to millions of degrees, so it glows brilliantly. But it’s only about the size of our solar system, so its brightness can change quickly.

That brightness depends on the mass of the black hole and the amount of material it’s ingesting. Astronomers recently discovered a distant quasar that’s more than 400 million million times brighter than the Sun. It’s powered by a black hole that’s 12 billion times the Sun’s mass — one of the heaviest black holes yet seen. More about that tomorrow.


Script by Damond Benningfield, Copyright 2015

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