spaceSpace and Physics

The Milky Way’s Supermassive Black Hole Has Gotten More Active Over The Last Two Decades


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockSep 12 2019, 18:20 UTC

Watchara Tongnoi/Shutterstock

Researchers recently observed a peculiar flare from Sagittarius A*, the supermassive black hole at the center of the Milky Way. Last May, they watched as the supermassive black hole increased in brightness and then quickly dimmed over just a few hours.

As reported in a new paper published in the Astrophysical Journal Letters, something has changed in the environment around Sagittarius A*. For over 20 years, researchers have been monitoring the infrared emissions of our friendly neighborhood supermassive black hole, and it appears that this year it became significantly more active.


The May flare was twice the brightness of the previous record holder for a black hole. The team looked at more than 13,000 observations over 133 nights since 2003. There have been two other bright nights this year, although not quite as remarkable as May 13.

“We have never seen anything like this in the 24 years we have studied the supermassive black hole,” Andrea Ghez, UCLA professor of physics and astronomy and a co-senior author of the research, said in a statement. “It’s usually a pretty quiet, wimpy black hole on a diet. We don’t know what is driving this big feast.”

The team found evidence that suggests the changes witnessed this year are unlikely to be the norm, at least following the current model for Sagittarius A*. There is only a probability of 0.05 percent for these observations to be part of a standard, unchanging behavior for a celestial body.


“The first image I saw that night, the black hole was so bright I initially mistook it for the star S0-2, because I had never seen Sagittarius A* that bright,” added lead author Tuan Do, also at UCLA. “But it quickly became clear the source had to be the black hole, which was really exciting.”

And S0-2 is being accused of having something to do with it. This star orbits close to the supermassive black hole, close enough in fact for the team to use it as a test-ground for general relativity. The star had its closest passage last year, which might have pushed some material into the jaws of the supermassive black hole.

An alternative suggestion is that we are witnessing a delayed reaction from the close passage of the dusty object G2 in 2014. The team is quite upfront in saying that maybe it’s the model that actually needs updating. As is often the case in astronomy, more observations will provide new insights to reach a satisfactory answer.


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