Telescopes show that the Milky Way’s black hole is ready to blast off

Telescopes show that the Milky Way’s black hole is ready to blast off

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This artist’s illustration depicts the results of a new study of the supermassive black hole at the center of our galaxy called Sagittarius A* (abbreviated Sgr A*). As reported in our recent press release, this finding finds that Sagittarius A* is rotating so fast that it distorts spacetime – that is, time and the three dimensions of space – so that it can look more like a football. Credit: Chandra X-ray Centre

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This artist’s illustration depicts the results of a new study of the supermassive black hole at the center of our galaxy called Sagittarius A* (abbreviated Sgr A*). As reported in our recent press release, this finding finds that Sagittarius A* is rotating so fast that it distorts spacetime – that is, time and the three dimensions of space – so that it can look more like a football. Credit: Chandra X-ray Centre

The supermassive black hole at the center of the Milky Way is spinning so fast, warping the spacetime surrounding it into a shape that could look like a football, according to a new study using data from NASA’s Chandra X-ray Observatory and the National Science Center. Karl G. Jansky Very Large Array (VLA) Foundation.

Astronomers call this giant black hole Sagittarius A* (Sgr A* for short), which is located about 26,000 light-years from Earth in the center of our galaxy.

Black holes have two basic properties: their mass (how much they weigh) and their spin (how fast they spin). Determining either of these values ​​tells scientists a lot about any black hole and how it behaves.

A team of researchers has applied a new method that uses X-rays and radio data to determine how fast Sgr A* is rotating based on how material flows toward and away from the black hole. They found that Sagittarius A* rotates at an angular speed — the number of revolutions per second — that is about 60% of the maximum possible value, the limit set by matter that is unable to travel faster than the speed of light.

In the past, various astronomers have made several other estimates of Sagittarius A*’s rotation speed using different techniques, with results ranging from Sagittarius A* not rotating at all to it rotating at almost the maximum rate.

“Our work may help resolve the question of how fast the supermassive black hole in our galaxy is rotating,” said Ruth Daly of Pennsylvania State University, lead author of the new study. “Our results suggest that Sagittarius A* is rotating very rapidly, which is interesting and has far-reaching implications.”


Credit: Chandra X-ray Centre

The rotating black hole pulls in “space-time” (the combination of time and the three dimensions of space) and nearby matter as it spins. The spacetime surrounding the rotating black hole is also being crushed. If we look at a black hole from above, along the nozzle of any jet it emits, we find that spacetime is circular. However, when looking at the rotating black hole from the side, spacetime is shaped like a football. The higher the spin speed, the flatter the soccer ball becomes.

The rotation of a black hole can serve as an important source of energy. Supermassive black holes can produce parallel outflows, that is, narrow jet-like bundles of matter, when their spin energy is extracted, which requires at least some matter to be present in the vicinity of the black hole.

Because of the limited fuel around Sagittarius A*, this black hole has been relatively quiet in the last few thousand years with relatively weak jets. However, this work shows that this can change if the amount of material near Sgr A* increases.

“The rotating black hole is like a rocket on a launch pad,” said co-author Benny Sebastian from the University of Manitoba in Winnipeg, Canada. “Once the material gets close enough, it’s as if someone fueled the rocket and pressed the ‘launch’ button.”


Chandra X-ray image of Sagittarius A* and the surrounding area. Credit: NASA/CXC/University. From Wisconsin / Y.Bai, et al.

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Chandra X-ray image of Sagittarius A* and the surrounding area. Credit: NASA/CXC/University. From Wisconsin / Y.Bai, et al.

This means that in the future, if the properties of matter and the strength of the magnetic field near the black hole change, part of the enormous energy of the black hole’s rotation could trigger even more powerful outflows. This source material could come from gas or the remains of a star being torn apart by the black hole’s gravity if that star wanders close to Sgr A*.

“Jets powered and collimated by a galaxy’s rotating central black hole can profoundly affect the gas supply of an entire galaxy, affecting how quickly stars form and even whether stars can form,” said co-author Megan Donahue of Michigan State University. “Fermi bubbles visible in X-rays and gamma rays around the Milky Way’s black hole show that the black hole may have been active in the past. Measuring the spin of our black hole is an important test of this scenario.”

more information:
Ruth A Daly et al., New black hole spin values ​​for Sagittarius A* obtained using the outflow method, Monthly Notices of the Royal Astronomical Society (2023). doi: 10.1093/mnras/stad3228

Magazine information:
Monthly Notices of the Royal Astronomical Society

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