Swirling gas helps scientists nail down Milky Way’s supermassive black hole mass

Astronomers from the Max Planck Institute for Extraterrestrial Physics have accurately determined the mass and radius of the supermassive black hole, Sagittarius A*, at the center of our galaxy. The black hole has a mass of 4.297 million solar masses and a radius smaller than Venus’ orbit around the sun. The team used data from the Very Large Telescope Interferometer to track electromagnetic emissions of gas surrounding the black hole.

The astronomers analyzed flares observed in 2018, 2021, and 2022, which allowed them to estimate the black hole’s mass with a high level of accuracy. The results were consistent with previous estimates, which were based on the orbital trajectories of stars around Sagittarius A*. The new findings are considered more reliable as they are closer to the black hole than the stars used in previous measurements.

The team calculated the mass of Sagittarius A* using the concept of “gravitational radii,” which is related to the radial distance of an object and is proportional to its mass. For Sagittarius A*, the gravitational radii represent the distance from the black hole’s center to its event horizon, the boundary beyond which nothing can escape the black hole’s gravitational pull. The gravitational radii of Sagittarius A* was found to be roughly 0.1 astronomical units, or one-tenth the distance from Earth to the sun.

The researchers are hopeful that these measurements can provide insights into the formation of structures in the Galactic Center. They also believe that the data collected from the flares could eventually reveal information about the black hole’s spin, which remains a mystery.