As astronomers obtained the first precise measurements of gamma radiation from the centre of our galaxy, the Milky Way, they were surprised to find a high density of gamma-ray sources. These objects, possibly related to interacting binaries, further puzzled astronomers by their constant variation of intensity. Even more mysterious is the object hiding in the heart of our galaxy. Images taken with radio telescopes of the centre of the Milky Way show a source called Sagittarius A* (Sgr A* in short), these images combined with a study of the velocity of stars near the centre indicates a hidden object of millions of solar masses, believed to be a massive black hole. But if Sgr A* is a black hole, it should, like other active nuclei emit X-rays and gamma-rays, contrary to the present evidence. The environment could explain this apparently weak activity. Up to now high energy radiation has never been detected from Sgr A*, possibly due to the lack of sensitivity of previous gamma-ray satellites. INTEGRAL will spend a lot of time scanning the centre of our galaxy, trying to detect these X-rays and gamma-rays, the last sign of matter swallowed by a black hole.
Last Update: 18 Mar 2008