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

Q:
I have been told that our Sun is a medium size star, and that there are other stars which may be several times more massive than our Sun. Also, I have read on your website that black holes are stars which are 3 times as massive as our sun.

Does this mean that no shining star has a mass more than 3 times that of our Sun?

A:
It is true, our Sun is a medium sized star, and other ones exist that are much more massive. The key idea is that when a star runs out of nuclear fuel it collapses, and if the core of the collapsing star has a mass of more than 3 times the Sun's mass, it will collapse all the way to a black hole. However, there are many stars with greater than 3 times the Sun's mass that are still shining, they haven't run out of their fuel yet.

Black holes can form from collapsing stars but we believe they may also form by other methods that are mysterious to us. So a black hole can be of stellar mass size, or millions of times of the mass of our Sun. We have an explanation of this in two places on the Chandra web site. Details on black holes at:
http://chandra.harvard.edu/learn_bh.html

Descriptions of three different types of black holes, stellar mass, mid-mass, and supermassive, may be found at:
http://chandra.harvard.edu/xray_sources/blackholes.html