It appears that every massive galaxy hosts a supermassive black hole in its centre.  A recent article in the journal Nature described the discovery of black holes as massive as 10 billion Suns.  Even by supermassive black hole standards, that’s pretty big.  For some perspective, the black hole in the centre of our Galaxy is about 4 million times the mass of the Sun (or about a 2500 times smaller).  Is there some upper limit to the mass of black holes?  Probably, because they only seem to grow to be a fixed fraction (about 0.3%) of the mass of the galaxies they live in.  We’re still working on figuring out how black holes and their host galaxies can grow in tandem.

Here is the orginal Nature article, and a discussion of the result in the New York Times.

This is an optical image of NGC 4889, an elliptical galaxy that hosts one of the big black holes profiled in the article.