“It’s like finding the needle in a haystack,” said Eduardo Bañados, an astronomer at the Carnegie Institution for Science who led the international research team. Their double discovery is described in a study published Wednesday in Nature.
Black holes, mysterious as they are, are among the most recognizable astronomical phenomena in popular science. They’re pretty straightforward: Black holes are spots in space where the tug of gravity is so strong that not even light can escape. They gobble up gas and dust and anything that comes near, growing and growing in size. A supermassive black hole sits in the center of virtually all large galaxies, including the Milky Way. Astronomers can infer their existence by watching fast-moving stars hurtle around a seemingly empty, dark region.
Quasars, meanwhile, are a little trickier to understand, and you’d be forgiven for thinking they sound like something out of Star Trek. A quasar is, to put it simply, the product of a binge-eating black hole. A black hole consumes nearby gas and dust inside a galaxy with intense speed, and the violent feast generates a swirling disk of material around it as it feeds. The disk heats up to extreme temperatures on the order of 100,000 degrees Kelvin and glows brightly. The resulting light show is what we call a quasar, and what a light show it is.
“A quasar emits more light than an entire galaxy’s worth of stars, and it’s actually just a glowing disk of material that is the size of our solar system,” said Daniel Mortlock, an astrophysicist at Imperial College London and Stockholm University. In 2011, Mortlock and his colleagues reported their discovery of the most distant quasar found at the time.
The more material a black hole consumes, the bigger it becomes. Eventually, the black hole drains the surrounding area of material and has nothing to eat. The luminous disk around it shrinks and fades, and the quasar is extinguished. In this way, quasars—and the black holes that power them—are like volcanoes, erupting under one set of conditions and settling into dormancy under another.
Quasars were first detected in 1963 by the Dutch astronomer Maarten Schmidt with California’s Palomar Observatory. Astronomers thought these newly discovered points of light were stars because of their extreme brightness. But when they studied the spectrum of their light, they were stunned to find the “stars” were more than a billion light-years away. When light travels through space, it gets stretched thanks to the constant expansion of the universe. As it moves, it shifts toward redder, longer wavelengths. Astronomers can measure this “redshift” to figure out how long the light took to reach Earth, which indicates how far a certain object is. Schmidt and his fellow astronomers knew that for stars to appear so luminous to Earth from such great distances was impossible. They were dealing with completely new phenomena.