Q:
Could you please tell me which is more common in our Galaxy: white dwarfs or black holes? Why?
A:
The answer is that we don't know. Certainly when we look at our galaxy we see mostly stars, many many stars. So at first you might think that since it is common for stars to end their lives as white dwarfs, slowly cooling off forever, that there might be more white dwarfs than black holes in the Milky Way. However, we have to remember that data suggests a huge sphere of dark matter around the Milky Way, matter that we cannot see in any wavelength we've looked so far but which is detectable through its gravitational effects. We don't know what this dark matter is made of, it could be made of either white dwarfs or black holes, some combination of both, or neither. So, we can't answer your question yet!
It seems that the contents of the Milky Way and of the universe itself are very mysterious! Some related material on dark matter is available at
http://chandra.harvard.edu/chronicle/0403/dark/index.html
We have a lot of information on white dwarfs on the Chandra web pages:
http://chandra.harvard.edu/xray_sources/white_dwarfs.html
and also on black holes:
http://chandra.harvard.edu/xray_sources/blackholes.html
Using our search button within the Chandra pages will turn up even more information, questions from other people, multimedia information, and more.
Revised: September 23, 2008