The first radio signal from Sagittarius A*? HST images of Centauri, a dense cluster of stars close to the Solar System
Most black holes have been found over the past half century by detecting radiation such as X-rays or radio waves3 produced by superheated gas that’s spiralling into the hole; the first hint of the presence of Sagittarius A* was indeed a radio source — albeit not a very bright one. No emissions have been found in the area.
The black hole could be at least 8,200 times as big as the Sun, according to astrophysicists, who studied 20 years of Hubble Space Telescope pictures.
Astrophysicist Maximilian Häberle at the Max Planck Institute for Astronomy in Heidelberg, Germany, and his collaborators examined more than 500 images of ω Centauri, a dense cluster of 10 million stars around 18,000 light years (5.43 kiloparsec) from the Solar System. The images were mostly taken to help calibrate Hubble’s instruments over the years.
This suggested that the stars had been accelerated by the gravitational pull of a massive object, such as a black hole. It would need to be at least 8,200 solar mass, but it could weigh as many as 50,000 suns. “We did not know before whether we would find it or not,” says Häberle. It was a little risky and we might have found nothing.