Our Galaxy's Black Hole Mysteriously Flared Up, Almost 75 Times Brighter And Nobody Knows Why

Our Galaxy's Black Hole Mysteriously Flared Up, Almost 75 Times Brighter And Nobody Knows Why

Scientists are still trying to understand why the black hole at the center of the Milky Way, known as Sagittarius A*, became 75 times brighter in just two hours back in May.

The gravity of a black hole is so strong that not even light can escape. Even if a bright star is shining right next to a black hole, you cannot see the black hole. Instead of reflecting the light as other objects do, the black hole just swallows the starlight forever.

But when the supermassive black hole called  Sagittarius A* (Sgr A*)  that lives at the center of our galaxy suddenly flared up and grew 75 times brighter for a few hours back in May, astrophysicists around the world were left completely baffled. 



On the night of May 13, 2019, astronomer Tuan Do of the University of California Los Angeles and his colleagues were watching Sgr A* using the Keck Telescope on the summit of Mauna Kea in Hawai’i. In a period of just two hours, they witnessed the black hole become 75 times brighter in the near-infrared band of the light spectrum.

"I was pretty surprised at first and then very excited,"  Tuan told ScienceAlert. , “The black hole was so bright I at first mistook it for the star S0-2, because I had never seen Sgr A* that bright. Over the next few frames, though, it was clear the source was variable and had to be the black hole. I knew almost right away there was probably something interesting going on with the black hole.”



“The brightness of Sgr A* varies all the time, getting brighter and fainter on the timescale of minutes to hours—it basically flickers like a candle,” Tuan said. “We think that something unusual might be happening this year because the black hole seems to vary in brightness more, reaching brighter levels than we've ever seen in the past.”

Black holes inherently don't emit any radiation that can be detected by our current instruments, but they can be used to collect the immense friction that is generated by the black hole's gravitational force, and that in turn produces measurable radiation. Yes, Science is fun, but also complex! 



"One of the possibilities," continued Tuan, "is that the star S0-2, when it passed close to the black hole last year, changed the way gas flows into the black hole, and so more gas is falling on it, leading it to become more variable." S0-2, which is about 15 times as massive as the Sun, may have been the object that juiced Sgr A."

In 2018, S0-2 came within 17 light hours of the supermassive black hole, and that close pass may have disturbed gases at the event horizon enough to cause the May 2019 brightening event. In any case, this unusual sparkle at the galactic core was likely caused by close encounters between Sgr A* and objects surrounding it, according to the team.



The edge of a black hole, called an event horizon, is shaped by intense tidal forces that tear at anything that gets close. Once a black hole starts devouring nearby objects like stars or gas clouds, infalling material heats up at the event horizon, sparking light shows that can be picked up by telescopes.

“Maybe the black hole is waking up—there's a lot we don't know at this point so we need more data to understand if what we are seeing is a big change in what is feeding the black hole or this is a brief event,” Tuan concluded. 


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