Microquasars in our Galaxy: mysterious black holes with jets - by Dr Silvain Chaty

Our group at the Open University studies microquasars in our Galaxy. These are objects composed of a normal star orbiting around a black hole (see Figure 1). They are amongst the strangest, most fascinating objects in the Universe. A black hole is a very compact object, whose gravity is highly attractive and into which some matter falls, but from which nothing can escape, not even light.

In these binary systems, the black hole can attract (by gravity) matter from the star nearby. Since matter in orbit cannot directly fall onto this compact object, it will spiral for a long time, until it crosses the event horizon of the black hole, after which it is lost for ever and cannot be observed anymore. Before it crosses the event horizon, matter accumulates in an accretion disc. From time to time, part of the matter of the star that is attracted by the black hole is swallowed and the rest is ejected by an unknown mechanism.