In the bizarre gravitational environment at the center of our galaxy, astronomers have discovered a clump of gas orbiting our supermassive black hole at hypervelocity.
Its properties are helping astronomers explore the space around Sagittarius A* for answers about why the galactic center blinks and flares across the electromagnetic spectrum.
Their findings suggest that the black hole is surrounded by a clockwise disk of material that is modulated by a strong magnetic field.
And confirmed what we already knew: The space around black holes went crazy.
“We think we’re looking at a hot bubble that orbits around Sagittarius A* the size of Mercury, but completes a full cycle in about 70 minutes,” said Maciek Wielgus, an astrophysicist at Max Plan, Germany Gram Institute for Radio Astronomy.
“This requires an incredible speed of about 30% the speed of light!”
Sgr A* was a major moment of attention earlier this year when the Event Horizon Telescope collaboration released images of black holes that formed over the years.
Together, telescopes around the world have made observations of the Milky Way’s center, which combined reveal a doughnut-shaped ring of matter swirling around Sagittarius A*, heated to incredible temperatures.
One of the telescopes included in the collaboration is the Atacama Large Millimeter/submillimeter Array (ALMA), an array of radio telescopes located in Chile’s Atacama Desert.
While studying the ALMA data alone, independent of the other collaborations, Wielgus and colleagues noticed something interesting.
In April 2017, during data collection, an X-ray flare erupted from the center of the Milky Way. This happened purely as astronomers collected data for the Event Horizon Telescope project.
Previously, these long flares observed at other wavelengths were associated with hot air masses that were very close to the black hole and traveled at very high velocities.
“What’s really novel and interesting is that so far, such flares have only been clearly present in X-ray and infrared observations of Sagittarius A*,” explains Wielgus. “Here, for the first time, we see a very strong indication that orbital hotspots are also present in radio observations.”
These flares are thought to be the result of hot gas interacting with a magnetic field, and the team’s analysis of ALMA data supports this idea.
The hot spots emit strongly polarized or twisted light and display the signature of synchrotron acceleration — both of which occur in the presence of strong magnetic fields.
The glow in radio light may be the result of the hot spot cooling after the flare and becoming visible at longer wavelengths.
“We found strong evidence for the magnetic origin of these flares, and our observations give us clues about the geometry of the process,” said astrophysicist Monika Mościbrodzka of Radboud University in the Netherlands.
“The new data are very helpful in establishing a theoretical explanation for these events.”
The team’s analysis of the light showed that the hot spot is embedded in a hysteretic disk. That’s a disk of matter spinning around and into the black hole, but the speed is hindered by a magnetic field.
Through modeling that integrated the data, the team was able to provide stronger constraints on the shape and motion of this magnetic field, as well as the formation and evolution of hotspots within it.
But there’s still a lot we don’t know. Observing black holes is really difficult, and there are some odd differences compared to infrared observations of other flares.
The team hopes that future simultaneous infrared and radio observations of future hotspot flares will help eliminate these problems.
“Hopefully one day, we’ll be comfortable saying we ‘know’ what happened to Sagittarius A*,” Vierges said.
The research has been published in Astronomy and Astrophysics.