It's not the biggest black hole ever found, but it's astonishingly young. The giant appears to have swelled to its enormous size only 875 million years after the big bang, when the universe was just 6 percent of its current age. That's a surprise, astronomers report Wednesday in the journal Nature, because giant black holes are thought to grow relatively slowly by vacuuming up gas and even stars that venture too close.
"How do you build such a big black hole in such a short time?" asks Xue-Bing Wu of China's Peking University, lead author of the study.
Wu and his colleagues didn't see the black hole directly, since by definition it has such powerful gravity that nothing, including light, can escape from it. Instead, using telescopes in China, Hawaii, Arizona, and Chile, the team spotted a quasar, a powerful object lit by a brilliant glow of gas that heats up as it tries to squeeze itself into the black hole itself.
"This is the biggest monster we've ever detected in terms of luminosity," says Avi Loeb, chair of the Harvard astronomy department, who was not involved in the research. It's about 40,000 times as bright as the entire Milky Way, Loeb says.
All major galaxies, including the Milky Way, have massive black holes at their cores, but not all of these are surrounded by superheated gas. The ones that are are known as quasars. And here, too, the newly discovered object, known as SDSS J010013.021280225.8, is extreme.
Like all quasars, the new object looks like an ordinary star. It's just a pinpoint of light, even through the most powerful telescopes. Only when astronomers analyzed the light in detail did they realize how fast it's moving away from Earth, and thus how far away it is (in an expanding universe, the most distant objects fly apart from each other the fastest). That told them how long the light from the quasar has been en route to Earth: about 12 billion years.
The quasar's extraordinary brightness tells the astronomers just how powerfully gas is being heated, which in turn tells them how astonishingly massive the underlying black hole is. "We've seen other quasars from this period," says Wu, "but none of them has a mass of more than three billion times that of the sun."