How to See a Black Hole with Your Naked Eye and a Telescope

Could you see a black hole with your naked eye? All you need is a 20 cm telescope in order to see a nearby, active black hole, according to researchers.

Once in several decades, some black hole binaries undergo "outbursts" in which enormous amounts of energy are emitted from substances that fall into the black hole. Black holes themselves are commonly surrounded by an accretion disk, in which gas from a companion star is slowly drawn to the hole in a spiral pattern. Activities of black holes are typically observed through X-rays, generated in the inner portions of accretion disks where temperatures reach 10 million degrees Kelvin or more.

"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 Mariko Kimura, a master's student at Kyoto University, in a news release.

In this case, researchers obtained unprecedented amounts of data from V404 Cygni, one of the black hole binaries thought to be nearest to Earth. They found that this black hole "woke up" after 26 years of dormancy.

In this case, the researchers can use a low-powered telescope to see the activity in visible light. It looks like flickering light, which emerges from gases surrounding the black hole.

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

The findings are published in the journal Nature.

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