One of the most enigmatic stellar systems in our Milky Way Galaxy has been shown to harbour a very massive black hole. With 14 times more mass than the Sun, this is the heaviest known stellar black hole in the Galaxy.

Using the ISAAC instrument on the VLT 8.2-m ANTU telescope at the ESO Paranal Observatory, an international team of astronomers peered into a remote area of the Milky Way to probe the binary system GRS 1915+105, located almost 40,000 light-years away.

They were able to identify the low-mass star that feeds the black hole by means of a steady flow of stellar material. A detailed follow-up study revealed how this star revolves around its hungry companion. The analysis of the orbital motion then made it possible to estimate the mass of the black hole.

The observation of the heavy black hole in GRS 1915+105 is opening up fundamental questions about how massive stellar black holes form, and whether or not such objects rotate around their own axes.

The team consists of Jochen Greiner, Mark McCaughrean (Astrophysical Institute Potsdam, Germany) and Jean-Gabriel Cuby (European Southern Observatory, Chile).

Read the details in ESO Press Release 24/01 (with three illustrations and all weblinks), available at

Editor’s notes

Additional Contact

Jochen Greiner
Astrophysical Institute Potsdam
Potsdam, Germany
Tel.:+49 331 7499 532

Peer reveiwed publication and references

The research described in this Press Release will appear in “GRS 1915+105 – An unusually massive stellar black hole in the Galaxy” by Jochen Greiner, Mark McCaughrean and Jean-Gabriel Cuby in the November 29, 2001, issue of the science journal “Nature”.