Scientists Observe Visible Light from Black Hole

For 26 years, the black hole binary V404 Cygni was dormant. Then, a force awakened. On June 15, 2015, the black hole binary underwent an outburst, with the matter falling into it from its accretion disk emitting enormous amounts of energy, including X-rays.

Now, an international team of scientists who studied the active black hole are reporting these outbursts are detectable via visible light. The team’s study was published in Nature.

“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,” said the study’s lead author Mariko Kimura, of Kyoto Univ.

Flashes emanating from the gases surrounding the black hole was an indication of the activity. According to Kyoto Univ., the activity was observable through a 20 cm telescope.

The accretion disk surrounding a black hole is comprised of gas, which is siphoned off from a nearby star and drawn into the hole in a spiral pattern. Observable X-rays typically come from the disk’s inner portion, an area which can reach temperatures over 10 million Kelvin. “These X-rays irradiate and heat the outer region of the disk, making it emit optical rays and thus becoming visible to the human eye,” according to Kyoto Univ.

The optical fluctuation patterns, according to the researchers, correlated to the X-ray patterns.

“Stars can only be observed after dark, and there are only so many hours each night, but by making observations from different locations around the globe we’re able to take more comprehensive data,” said study co-author Daisuke Nogami. “We’re very pleased that our international observation network was able to come together to document this rare event.”

The observed flashes lasted from several minutes to a few hours. The activity stopped after two weeks.   

According to the researchers, black holes with nearby stars experience such outbursts once every several decades.

The Guardian reports that the studied black hole is one of the closest to the Earth at 8,000 light-years.