Scientists Spy Never-Before-Seen Halo of Cool Gas Circling the Milky Way’s Supermassive Black Hole Sagittarius A*

Thursday, 06 June 2019 - 12:06PM
Black Holes
Astrophysics
Thursday, 06 June 2019 - 12:06PM
Scientists Spy Never-Before-Seen Halo of Cool Gas Circling the Milky Way’s Supermassive Black Hole Sagittarius A*
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NRAO/AUI/NSF; S. Dagnello CC BY 3.0

Well, that was unexpected.

Nobody had any idea that there is a halo of cool gas circling the black hole at the center of our galaxy until a team of researchers at the ALMA observatory in Chile's Atacama desert took a closer look. Their paper was published yesterday in Nature, the world's leading science journal.

Sagittarius A* is the supermassive black hole that sits some 26,000 light-years away in the center of our Milky Way galaxy with a mass approximately 4 million times that of our Sun. It is surrounded by something called an accretion disc, which is a wide, flat band of cosmic detritus that has not been swallowed into the gravitational abyss beyond the event horizon.

Within this accretion disc, there is a ring of blisteringly hot gas. How hot? 18 million Fahrenheit, according to Science Alert – which lights up on X-ray observations like Times Square at its worst – but it didn't seem to be moving. This is atypical, to say the least.

Scientists found a loophole: hydrogen. The radiation surrounding Sagittarius A* causes hydrogen atoms to constantly gain and lose electrons, which produces a very distinct signal that can reach Earth with hardly any deterioration. Scientists used the ALMA (Atacama Large Millimeter Array) to image the hydrogen wavelength which revealed that not only was the accretion disc moving but that there was also a previously unknown ring of much cooler gas surrounding the black hole. They were then able to map the rotation by analyzing its redshift and blueshift (more on those phenomena here and here).



Image Credit: ALMA (ESO/NAOJ/NRAO), E.M. Murchikova; NRAO/AUI/NSF, S. Dagnello CC BY 3.0

Elena Murchikova, the lead author of the paper and an astrophysicist at the Institute for Advanced Study in Princeton, said in a statement:

"We were the first to image this elusive disk and study its rotation…This is important because this is our closest supermassive black hole. Even so, we still have no good understanding of how its accretion works. We hope these new ALMA observations will help the black hole give up some of its secrets."

Watch how scientists go about finding black holes here:



Cover Image Credit: NRAO/AUI/NSF; S. Dagnello CC BY 3.0

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