Visible light emitted from a black hole has been detected for the first time

For the first time, astronomers have observed bursts of visible light being released by a black hole as it swallows matter from nearby stars.

These flashes of light, which lasted between several minutes to a few hours, were seen coming from a black hole in the Cygnus constellation, located about 7,800 light-years away from Earth. Incredibly, some of the flashes were so bright, the team says amateur astronomers could see them with a modest 20-cm telescope.


"We find that activity in the vicinity of a black hole can be observed in optical light at low luminosity for the first time," astronomer and lead researcher, Mariko Kimura from Kyoto University in Japan, told Charles Q. Choi at Space.com.

"These findings suggest that we can study physical phenomena that occur in the vicinity of the black hole using moderate optical telescopes without high-spec X-ray or gamma-ray telescopes."

Nothing - including light - can escape a black hole once it’s fallen in, but the process of swallowing gas, dust, or ripping apart whole stars can cause the formation of an accretion disk near the event horizon. These disks can thrust streams of plasma called relativistic jets across the entire length of a galaxy, while hitting temperatures of 10 million degrees Celsius (18 million degrees Fahrenheit) or more.

This insane heat can cause a black hole accretion disk to give off an incredibly bright glow, which is what Kimura and her team observed when they focussed in on V404 Cygni - an active black hole in the Cygnus constellation that reactivated on 15 June 2015 after 26 years of dormancy.

First detected by NASA's Swift space telescope, the event was then tracked by the Japanese researchers, who called on scientists from 26 locations around the world to point their optical telescopes at V404 Cygni.

For two weeks, the astronomers were able to observe flashes of light being released by the newly active V404 Cygni, which is one of the closest known black holes to Earth. It was woken up when the gravitational pull of its partner star pulled the two in too close, causing the black hole to strip away the surface matter of the star, before the whole thing fell in to release an incredible burst of radiation.

For the first time, astronomers have witnessed the light produced by this event using an optical telescope.

Publishing in Nature today, the team hypothesises that the light originates from X-rays produced in the centre of the accretion disk, and these X-rays irradiate and heat up the outer region of the disk, which causes it to emit optical rays.

While more research is needed to confirm this, it’s beyond exciting to think of how much more we stand to learn about black holes now that we have a new way of observing them - and it’s something anyone can help with if they have a good telescope at home.

"We're very pleased that our international observation network was able to come together to document this rare event," said co-author, Daisuku Nogami.