On a summer night last year, Michael Richmond was observing V404 Cygni, a binary system. Armed with a 12-inch telescope at the RIT Observatory in Rochester, New York – Richmond noticed the object dim to just 6% of its original brightness. The brightness then rose to about half its original level.

V404 Cygni animation

Here’s a graph showing the brightness changes over a nearly four-hour period.

V404 brightness changes

Credit: Michael Richmond/RIT

What’s going on here? V404 Cygni is a binary system. That means two objects are orbiting around each other. We know V404 Cygni is a variable star. But the other object is a black hole. And that’s what caused the dip in brightness.

What’s incredible is that astronomers observed the black hole using optical telescopes. That puts one of the most incredible stellar objects in reach for amateur astronomers.

“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,” explains lead author Mariko Kimura, a master’s student at Kyoto University. Kimura led a group of astronomers from Kyoto University that published a paper on the black hole system and various observations.

A black hole ‘outburst’

Last year’s observations of V404 Cygni were the first outbursts from the black hole binary since 1989. Astronomers from around the world gathered huge amounts of data from V404 Cygni. The team found the optical fluctuation patterns showed similar variations with the X-ray patterns.

That’s not what astronomers expected. Observations are usually done with X-ray telescopes because X-rays can travel through the outer disk and cooler gas surrounding the accretion disk. So, how is visible light seen? The astronomers think the X-rays are heating up gas in the outer regions. This heat leads to the emission of large amounts of visible light.

Why Scientists are Turning to an Algorithm to Image a Black Hole

Observing V404 Cygni was a worldwide effort. “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,” says co-author Daisaku Nogami. “We’re very pleased that our international observation network was able to come together to document this rare event.”

According to Richmond, more than 85,000 optical measurements were gathered from across the world.

v404 observations

Credit: Kyoto University

Being able to observe binary systems like V404 Cygni with small optical telescopes is pretty damn awesome. Have an 8-inch telescope lying around? Maybe you’ll be a part of a similar study.

You can read more about Michael Richmond’s observations of V404 Cyngi here. And a more in-depth explanation from Kyoto University here. The study is behind a paywall, but these two links cover most of the research.

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