A violent burst of flickering visible light created as matter falls into a black hole has been detected for the very first time, astronomers say.
The phenomenon, which is yielding insights into how matter swirls into a black hole, is visible to anyone with just a moderate-sized telescope, the research team says.
Nothing escapes once in the clutches of a black hole, not even light — thus the name — but the dust and gas falling into one gets superheated to the point where the matter glows brightly just before it disappears into the black hole.
It's this glow that Japanese researchers detected around the active black hole V404 Cygni in June of last year.
Awakening from a 26-year period of little activity, it emitted flashes of light that were spotted by telescopes, the researchers report in the journal Nature.
The flashes, lasting from a few minutes to several hours, could be seen by amateur astronomers with a 7-inch telescope, they said.
Previously, these kinds of outbursts from black holes had only been detected through intense emissions of X-rays or gamma-rays, they noted. In fact, it was the detection of such rays bursting from V404 Cygni that prompted the Japanese team to contact colleagues around the world to focus optical telescopes on the black hole.
"We now know that we can make observations based on optical rays — visible light, in other words — and that black holes can be observed without high-spec X-ray or gamma-ray telescopes," says Mariko Kimura of Kyoto University.
V404 Cygni, in the constellation of Cygnus, the Swan, is a binary system — a black hole around nine times the mass of our sun paired with a companion star slightly less massive than the sun.
The two bodies orbit each other every 6-1/2 days.
At around 7,800 light-years away from Earth, the black hole in V404 Cygni is one of the closest to the Earth.
That provides a chance to better understand the nature of such extreme events as the flickering seen there, especially since it is visible with even modest telescopes, the researchers say.
"Thanks to international cooperation, we could get extensive optical observational data in our research with 35 telescopes at 26 locations," Kimura says. "We would like more people to join in optical observations of black-hole binaries."