Strange droplet of hot gas buzzes around Sagittarius A* with ‘mind-boggling speed’: ScienceAlert

Strange droplet of hot gas buzzes around Sagittarius A* with ‘mind-boggling speed’: ScienceAlert

In the strange gravitational environment at the heart of our galaxy, astronomers have found a glob of gas orbiting our supermassive black hole at superspeed.

Its features are helping astronomers probe the space immediately surrounding Sagittarius A* in search of answers as to why the galactic center flickers and lights up across the electromagnetic spectrum.

Their findings suggest that the black hole is surrounded by a disk of material that rotates in a clockwise direction modulated by a powerful magnetic field.

And it confirms something we already knew: the space around a black hole goes wild.

“We think we’re looking at a bubble of hot gas moving around Sagittarius A* in an orbit similar in size to the planet Mercury, but completing one cycle in only about 70 minutes,” says astrophysicist Maciek Wielgus of Max. Planck Institute for Radio Astronomy in Germany.

“This requires mind-boggling speed of about 30 percent of the speed of light!”

Sgr A* had a big moment in the spotlight earlier this year when the Event Horizon Telescope collaboration revealed an image of the black hole’s formative years.

Telescopes from around the world worked together to take observations of the galactic center, which combined to reveal the donut-shaped ring of material swirling around Sgr 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 the Atacama Desert in Chile.

While studying the ALMA-only data, isolated from the rest of the collaboration, Wielgus and his colleagues noticed something interesting.

In April 2017, in the midst of data collection, the galactic center released an X-ray flare. It was purely by chance that it happened while astronomers were collecting data for the Event Horizon Telescope project.

Previously, these long flares, observed at other wavelengths, have been associated with droplets of hot gas orbiting very close to the black hole and at very high speeds.

“What is really new and interesting is that such flares were so far only clearly present in X-ray and infrared observations of Sagittarius A*,” explains Wielgus. “Here we see for the first time a very strong indication that orbiting hot spots are also present in radio observations.”

These flares are thought to be the result of the hot gas interacting with a magnetic field, and the team’s analysis of the ALMA data supports this idea.

The hot spot emits light that is strongly polarized or twisted and shows the signature of synchrotron acceleration, both of which occur in the presence of a strong magnetic field.

And the glow in radio light could be the result of the hot spot cooling after the flare and becoming visible at longer wavelengths.

“We found strong evidence for a magnetic origin of these flares and our observations give us a clue about the geometry of the process,” says astrophysicist Monika Mościbrodzka of Radboud University in the Netherlands.

“The new data is extremely helpful in building a theoretical interpretation of these events.”

The team’s analysis of the light suggests that the hot spot is embedded in a magnetically stopped disk. It is a swirling disk of material that is drawn into the black hole, but at a speed that is hampered by the 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, and the formation and evolution of the hotspot within it.

But there is still much we don’t know. Observing black holes is really hard, and there are some strange discrepancies compared to infrared observations of other flares.

The team hopes that simultaneous infrared and radio observations of future hot spot eruptions will help resolve these issues.

“Hopefully, one day, we’ll feel comfortable saying we ‘know’ what’s going on in Sagittarius A*,” says Wielgus.

The research has been published in astronomy and astrophysics.

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