Expert: Jayendra Upadhye - 3/6/2005

Question
Why is there an upper limit to the mass of neutron stars? And why is it not well known?

Answer
Alan,
There is an upper limit for the simple reason that beyond such a limit there is one more possible demise of the star in question. Which is, to become a black hole.
Regarding the second part of your question..
That is because, the pressures and temperatures involved are too hight to be handled in labs for experimental deductions.
Also to add to the difficulty, quantum mechanics is involved (degenerate matter involving close proximity of its nucleons).

This site actually will give the answer "straight from the horses mouth"!
http://einstein.stcloudstate.edu/nook/astr107/study/ch15/ch15.html

your answer is question 1 on that site, and it is in great detail..too much to be typed in here.

So give the credits to that site..
I am just a "marshalling agent" for you! :)
Jayen