At the middle of our galaxy sits a dark enigma, a supermassive black hole named Sagittarius A*. Astronomers have known concerning the existence of Sgr. A* for a while, and even snagged a spectacular image of it in 2022, but getting exact measurements of its size and activity have proven elusive.
But now, in recent findings from the Max Planck Institute for Extraterrestrial Physics (MPE), a gaggle of astronomers have determined, with high accuracy, the mass and radius of Sgr A*.
Specifically, Sgr A* was found to are available in at a whooping 4.297 million solar masses — with a radius smaller than that of Venus’ orbit across the sun. They deduced this information by studying the luminous gas present in this enormous void’s orbit.
Mainly, the researchers used data from the near-infrared interferometer on the European Southern Observatory’s Very Large Telescope Interferometer (VLTI) to trace electromagnetic emissions of gas swirling across the black hole. They were looking out for flares — shiny flashes of electromagnetic radiation which may occur a few times a day. These flares, in brief, allowed the astronomers to trace the motion of gas surrounding Sgr A*.
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The team analyzed flares observed in 2018, 2021 and 2022. This combined data allowed the researchers to estimate the mass of the black hole with a high level of accuracy, they are saying, which was necessary since it provides a brand new, independent measurement of the black hole’s mass. Thankfully, the outcomes sat in accordance with previous estimates.
Those prior measurements were based on the orbital trajectories of stars around Sgr. A*, but those stars are much further away than the newly measured flares seem like meaning the outcomes were technically less reliable.
The researchers consult with what’s generally known as “gravitational radii” in calculating the mass of Sgr. A*. The gravitational radii value of an object has to do with the radial distance of the item; it is also proportional to that object’s mass. For Sgr. A*, the radii represents the space from the middle of the black hole to the event horizon, which is the barrier between the observable universe and whatever’s contained in the black hole. Beyond the event horizon, even light gets overtaken by the black hole’s immense gravitational strength. The gravitational radii of Sgr A* turned out to be equal to roughly 0.1 astronomical units, or one tenth the space from the Earth to the sun.
While this might sound small, it’s actually relatively large, because the sun’s gravitational radii value is the same as roughly 3 kilometers (1.9 miles). This can also be the scale the sun would should be compressed to before it may possibly collapse right into a black hole.
”The mass we derived now from the flares at just a couple of gravitational radii is compatible with the worth measured from the orbits of stars at several thousand gravitational radii,” Diogo Ribeiro, who was answerable for the study’s theoretical modeling on the Max Planck Institute for Extraterrestrial Physics, said in a press release.
“This strengthens the case for a single black hole at the middle of the Milky Way,” he adds.
Researchers are also enthusiastic about what treasures these measurements might contain regarding the formation of structures within the Galactic Center. Based on Antonia Drescher, who was also involved within the study measurements, the orientation of the flare orbits hint at a physical reference to a stellar disk sitting much further away from the black hole.
”It’s great to see the repeated, similar behavior of the flares,” Drescher said within the statement. ”All of them show a clockwise looped motion on the sky; all have an identical radius and an identical orbital period. This is basically beautiful to see.”
The team hopes data collected from the flares may eventually provide the scientific community about information on the spin of the black hole too, something that also stays a mystery.
A study on these findings was published in September within the journal Astronomy & Astrophysics.