Astronomers Spot Mysterious Flash From Our Galaxy's Supermassive Black Hole

James Marshall
August 13, 2019

The black hole often flickers, but outbursts are incredibly rare.

What made the black hole turn bright so suddenly?

You don't usually think of a supermassive black hole as something that can go unnoticed, but many of these interstellar monsters are quite placid. The location of the black hole, a feature known to astronomers as Sagittarius A* (pronounced "Sagittarius A star") isn't easily visible from Earth, but scientists can still catch a glimpse of it using infrared cameras during certain times of the year. "I knew nearly right away there was probably something interesting going on with the black hole". Their findings so far are now in press with The Astrophysical Journal Letters. It's under constant observation with instruments like the WM Keck Observatory in Hawaii used by the UCLA team. Black holes themselves don't emit any radiation that can be detected by our current instruments, but the stuff nearby does when the black hole's gravitational forces generate huge friction, in turn producing radiation. It's possible a large volume of matter fell into the black hole's gravity well, and that caused the flash. However, the objects and material close to them do-and changes to the black hole can excite matter nearby, allowing scientists to detect changes taking place. As ScienceAlert reports, the research team has a couple of possibilities in mind. That was so unexpected that at first, he believed the flash came from a star in the same part of the sky called S0-2. One is G2, an object thought to be a gas cloud that approached within 36 light-hours of Sgr A* in 2014.

Researchers believe that the odd "glow" may relate to gas clouds or stars which orbit the enormous black hole. That's S0-2, a star on a long, looping, 16-year elliptical orbit around Sgr A*. There were no cosmic fireworks at the time, but we could be seeing a delayed reaction. It made its closest approach yet past year, coming within 17 light hours of the event horizon. They are now being collected, across a larger range of wavelengths.

Do told Science Alert, 'One of the possibilities, is that the star S0-2, when it passed close to the black hole past year, changed the way gas flows into the black hole, and so more gas is falling on it, leading it to become more variable'. Keck will be providing data for another few weeks, Do says, though after that point the Galactic center will not be at the right angle for observation again until 2020.

Luckily, there are plenty of sources for extra data to help fathom the cause of the change. However four other telescopes - including Spitzer, Swift, Chanrdra, and ALMA - have been making observations over the summer, with their data still to be released.

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