What is the max. mass of a neutron star?

Question

I've heard the 1.4 solar mass number thrown around, but I thought the Chandrasekhar Limit applied to white dwarfs - electron degenerate matter - not neutron degenerate matter

Answer 1

It isn't an issue of knowledge of neutron degeneracy; it depends on the degeneracy of various particle soups that result when you squish neutrons. Different hadrons and even quarks (if you can have free quarks.) You are right in essence; we don;t have a good enough understanding of the states of matter inside of a neutron star to understand its limit well.

I remember seeing a number of 2.44 M_sun in some book on black holes I had in grad school for a class.

Just now I found a couple of papers that touch on this topic (and none entirely ABOUT this topic, which probably means no one trusts their structure models well enough to make predictions). They are linked to below and both have mass estimates of observed neutron stars. Nothing like empiricism in my mind!

Anyway, doesn't look like anyone has seen one more massive than around 1.8 M_sun . That doesn't mean they don't exist, but since a lot of these are x-ray systems (and so it isn't a matter of them being so close to their Schwarzschild radii that no light like a pulsar hotspot can escape) this could be meaningful. It could also mean more massive ones are never in short period binary systems. . . maybe to be bigger, the starting star is so darn massive that its companions are always ejected after a supernova. Who knows.

Answer 2

The Chandrasekhar Limit is the mass above which electron degeneracy will not hold, which means it is the minimum mass required to form a neutron star. The upper limit thought to be around three solar masses. The physics of neutron degeneracy aren't understood well enough to put a precise figure, though. I've seen numbers ranging from 2 to 5 solar masses.

Answer 3

The typical neutron star has a mass between 1.35 and 2.1 solar masses. The source says that stars between 3 and 5 solar masses experience gravitational collapse, and inevitably a black hole is the product.

Read more about this from the source below.