Watch A Hotspot Orbit Our Galaxy's Black Hole - Sky ⁘ Telescope

Astronomers have used artificial intelligence to reconstruct a 3D video that shows a hot pocket of gas orbiting a stone's throw away from our galaxy's central black hole.

For all its "supermassive" status, our resident behemoth, dubbed Sgr A*, is quiet as such black holes go. Perhaps due to strong magnetic fields that constrict its diet, it only picks at the gaseous buffet around it. Even so, it emits minor flares up to several times a day at X-ray, infrared, and radio wavelengths.

These flares were a nuisance to the Event Horizon Telescope (EHT) team, which produced an image of Sgr A*'s dark silhouette, based off of data collected in 2017. Now, Aviad Levis (Caltech) and collaborators, including several members of the EHT team, have utilized some of this 2017 data for a new project: following the motion of a flaring hotspot in the tumultuous gas flowing around the black hole.

The Atacama Large Millimeter/submillimeter Array (ALMA), high in the Atacama Desert in Chile, was imaging Sgr A* on April 11, 2017, as part of the EHT project. While data taken earlier in the month was ultimately used for the EHT image, because the black hole was quieter then, the radio-wave data collected on April 11th was interesting in its own right, as it coincided with an X-ray flare.

However, while the combined EHT data revealed an exquisitely high-resolution image of Sgr A*, the ALMA data taken alone is 100,000 times fuzzier. Basically, all of the information that the team was interested in was packed into a single pixel.

The researchers started with the idea that flares come from hotspots within gas flowing around the central maw. Magnetic fields snap-crackle-popping very close to the black hole can heat and energize this gas.

If a flare comes from such a hotspot, then information about the flare's origin is encoded in the pixel's changing brightness: Gas flowing into the black hole won't change much over a few hours, but hot pockets of gas will shear out and fade more quickly. The radio waves' polarization , which tells us at what angle the light waves are oscillating, is also expected to be higher when the light is coming from a hot bubble of plasma.

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