Astronomers See “Sparkles” Around The Milky Way’s Supermassive Black Hole

Artist’s impression of the gaseous disk around the supermassive black hole. Hot spots circling around the black hole could produce the quasi-periodic millimeter emission detected with ALMA. Keio University

Astronomers are aware the supermassive black hole at the center of the Milky Way occasionally flares due to clouds of material suddenly being absorbed. These are not, however, the only emissions detected near the black hole. Researchers report the detection of flickering at millimeter wavelengths.

These newly discovered "sparkles" are quasi-periodic variations that are less intense than flares previously detected around the black hole we call Sagittarius A* (Sgr A*). The observations, published in the Astrophysical Journal Letters, were conducted with the Atacama Large Millimeter/submillimeter Array (ALMA). The team suggest the emission is consistent with material going around on the innermost stable orbit, which is less than 10 million kilometers (6 million miles) from the surface of the black hole.


“It has been known that Sgr A* sometimes flares up in millimeter wavelength,” lead author Yuhei Iwata, a graduate student at Keio University, Japan, said in a statement. “This time, using ALMA, we obtained high-quality data of radio-wave intensity variation of Sgr A* for 10 days, 70 minutes per day. Then we found two trends: quasi-periodic variations with a typical time scale of 30 minutes and hour-long slow variations.”

The cause of these variations is not certain, but the team proposes a scenario that involves the formation of hot spots of material within the disk. The disk is under the incredible gravitational pull of the black hole and is rotating around Sagittarius A* at over one-third of the speed of light. These incredible conditions might create the amplified emission seen by ALMA.

These changes and the possibility of studying them are exciting to better understand black holes, but it's not good news for the Event Horizon Telescope. The collaboration was able to snap the first-ever picture of a black hole last year. In their campaign of observations, they also observed Sagittarius A* but they reported that the analysis of that data was a lot more complex than the M87 one that was published.

“In general, the faster the movement is, the more difficult it is to take a photo of the object,” stated co-author Professor Tomoharu Oka, also at Keio University. “Instead, the variation of the emission itself provides compelling insight for the gas motion. We may witness the very moment of gas absorption by the black hole with a long-term monitoring campaign with ALMA.”


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