The latest findings from a new study resolved the puzzle around the speedy rotation of the Milky Way’s supermassive black hole, Sagittarius A* (Sgr A*). The black hole, containing about 4 million times the mass of the Sun, exhibited rapid spin as detected by NASA’s Chandra X-ray Observatory and the NSF’s Very Large Array. This high speed of rotation has caused the spacetime around Sgr A* to take on the shape of an American football.
A team of scientists utilized a novel method combining X-ray and radio data to establish Sgr A*’s rotational speed based on the flow of material toward and away from the black hole. The study revealed that Sgr A* is spinning at an angular velocity of around 60% of the maximum possible value and with an angular momentum of approximately 90% of the maximum possible value.
The black hole’s speedy spin has led to the squashing of spacetime around it, shaping it into a football-like structure. In addition, the illustration also depicts the gas swirling around Sgr A* in a disk, with jets firing away from the poles of the spinning black hole. The faster the spin, the flatter the football shape becomes.
The spin of a black hole serves as a crucial source of energy, as it produces collimated outflows, such as jets, when the spin energy is extracted. However, Sgr A* has been relatively quiet in recent millennia due to limited fuel in its vicinity. This new study suggests that the situation could change if the amount of material around Sgr A* increases.
To determine Sgr A*’s spin, the researchers used the “outflow method,” which details the relationship between the spin of the black hole, its mass, the properties of the matter near the black hole, and the outflow properties. The combination of data from Chandra and the VLA with an independent estimate of the black hole’s mass from other telescopes was employed to constrain the black hole’s spin.
The findings of this study were published in the January 2024 issue of the Monthly Notices of the Royal Astronomical Society. The authors of the research include Ruth Daly (Penn State University), Biny Sebastian (University of Manitoba, Canada), Megan Donahue (Michigan State University), Christopher O’Dea (University of Manitoba), Daryl Haggard, and Anan Lu (McGill University).
