Sgr A* Just Flared Up And No One Knows Why

The massive black hole at the center of the Milky Way, also known as the Sagittarius A* or Sgr A* just lit up and no one really knows why. In May, it became 75 times brighter than usual within a couple of hours.

Sagittarius A* is the supermassive black hole around at the center of Milky Way, around which everything in our galaxy revolves. It is a compact astronomical radio source that is 4 million times as massive as the Sun. Though no light escapes its boundaries, astronomers can observe the hole’s interactions with bright stars or dust clouds that surround it.

Sgr A*
Chandra Image of Sgr A* (Image: NASA)

On the night of May 13, 2019, UCLA astronomer Tuan Do and his colleagues were watching Sgr A* using the Keck Telescope on the summit of Mauna Kea in Hawaii. 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.

“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,” Do 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.”

Also Read: The 3 types of Black Holes

Do and his colleagues speculate that a star called 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.

“Many astronomers are observing Sgr A* this summer,” Do noted. “I'm hoping we can get as much data as we can this year before the region of the sky with Sgr A* gets behind the Sun and we won't be able to observe it again until next year.”

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