Sagittarius A*, the 4.3 million solar mass black hole at the center of the Milky Way, is spinning so fast that it is warping the space-time around it into a shape that may resemble a ball of football, according to an analysis. from data collected by NASA’s Chandra X-ray Observatory and NSF’s Karl G. Jansky Very Large Array.
Black holes have two fundamental properties: their mass (how much they weigh) and their spin (how fast they spin).
Determining either of these two values tells astrophysicists a lot about any black hole and how it behaves.
Dr. Ruth Daly and her colleagues at Penn State University applied a new method that uses radio and X-ray data to determine how fast Sagittarius A* spins based on how material flows to and from the black hole.
They discovered that Sagittarius A* rotates with an angular velocity (number of revolutions per second) that is about 60% of the maximum possible value, a limit imposed by the fact that the material cannot travel faster than the speed of light.
In the past, different astronomers made various other estimates of Sagittarius A*’s rotation speed using different techniques, with results ranging from Sagittarius A* not rotating at all to spinning at almost maximum speed.
“Our work may help resolve the question of how fast our galaxy’s supermassive black hole is spinning,” Dr Daly said.
“Our results indicate that Sagittarius A* is spinning very rapidly, which is interesting and has far-reaching implications.”
A rotating black hole pulls in space-time and nearby matter as it spins. The spacetime around the rotating black hole is also crushed.
Looking at a black hole from above, along the barrel of any jet it produces, spacetime has a circular shape.
However, if you look at the spinning black hole from the side, spacetime is shaped like a soccer ball. The faster the spin, the flatter the ball will be.
The spin of a black hole can act as an important source of energy. Spinning supermassive black holes can produce collimated flows, that is, narrow beams of material like jets, when their spin energy is extracted, which requires that there be at least some matter in the vicinity of the black hole.
Due to fuel shortages around Sagittarius A*, this black hole has been relatively quiet in recent millennia with relatively weak jets.
However, the new study shows that this could change if the amount of material in the vicinity of Sagittarius A* increases.
“Jets driven and collimated by a galaxy’s rotating central black hole can profoundly affect the gas supply for an entire galaxy, affecting how quickly and even how well stars form,” said Dr. Megan Donahue. , astronomer at Michigan State University.
“Fermi bubbles seen in X-rays and gamma rays around our Milky Way’s black hole show that the black hole was probably active in the past. “Measuring the spin of our black hole is an important test of this scenario.”
To determine the spin of Sagittarius A*, astronomers used an empirically based theoretical method called the outflow method, which details the relationship between the black hole’s spin and its mass, the properties of matter near the black hole, and the output properties.
The collimated flow produces radio waves, while the gas disk surrounding the black hole is responsible for the emission of X-rays.
Using this method, the researchers combined data from NASA’s Chandra X-ray Observatory and NSF’s Karl G. Jansky Very Large Array with an independent estimate of the black hole’s mass from other telescopes to constrain the black hole’s spin.
“We have a special view of Sagittarius A* because it is the closest supermassive black hole to us,” said Dr. Anan Lu, an astronomer at McGill University.
“Although it is quiet now, our work shows that in the future it will give an incredibly powerful boost to surrounding matter.”
“That could happen in a thousand or a million years, or it could happen in our lifetimes.”
He study was published in the Monthly Notices of the Royal Astronomical Society.
Ruth A. Daly et al. 2024. New black hole spin values for Sagittarius A* obtained with the outflow method. MNRAS 527 (1): 428-436; doi:10.1093/mnras/stad3228