Q&A: Normal Stars, White Dwarf Stars, and Star Clusters

Q:
I am interested in determining if the overall total black hole mass content of elliptical galaxies is usually less than that of typical spiral galaxies. Detection of stellar mass black holes in distant elliptical's is currently very difficult...Nevertheless, your Chandra team has revealed X-ray evidence for some black holes in binaries, particularly in globular clusters, of certain elliptical's like NGC 4697. Does this suggest that there is essentially no difference between spirals and elliptical's in their ability to create stellar mass black holes?

A:
This is a question that is very much under investigation by scientists using Chandra. One of the best studies so far is by E. Colbert et al.
They show that the number of X-ray binaries in spiral and elliptical galaxies depends on two factors: the total number of stars in the galaxy, and the star formation rate in a galaxy. Since X-ray binaries are not active for the entire age of the galaxy, star formation, which is more active in spirals, can produce an excess of sources. The conclusion from their study is that there is no evidence for an intrinsic difference in the numbers of neutron stars or black holes for elliptical versus spiral galaxies of the same mass.