I Low mass limit of a neutron star

1. Dec 11, 2017

snorkack

2. Dec 12, 2017

Black Holes, White Dwarfs and Neutron from Shapiro and Teukosky, at chapter 8. You may prefer to read the sumary at page 227.

3. Dec 12, 2017

Staff: Mentor

This talks about the cold equation of state above neutron drip, but the discussion of how this relates to the minimum mass of a neutron star doesn't occur until early in Chapter 9 (pp. 252-253). The minimum mass appears to be just below 1/10 of a solar mass, and to occur at a central density of $7 \times 10^{12} \text{g / cm}^3$. In the regime between $\rho_{\text{drip}}$ and this density, there are no stable solutions; so I'm not sure I would describe the minimum mass neutron star solution as a "superior limit" of a white dwarf solution. But I agree that the equation of state in this regime appears to be well understood, so the cold minimum mass limit given here should be reliable. (But as @Vanadium 50 has pointed out, the cold limit actually is not very useful practically, since the neutron stars we observe are not cold.)

4. Dec 12, 2017

This mass curve is obtained for HW equation of state, if one uses BPS-BBP the curve continues and has a minimum at a higher central density. I dont know if there is this curve plotted on this book, but these diferences of EoS are debated in page 48 figure 2.2. I have BPS-BBP mass curve plotted by myself also.

5. Dec 12, 2017

Staff: Mentor

I'm not sure which mass curve you're referring to, but the minimum neutron star mass I referred to, discussed on pp. 252-253 of the reference you gave, is clearly stated to be derived using the BBP equation of state. Since this thread is about the minimum mass for a neutron star, that would seem to be the relevant one.

6. Dec 12, 2017

Staff: Mentor

Oops, I see I misread the text; the density I quoted is the density at which $\Gamma$ rises above 4/3 again. The central density at which the minimum mass occurs is $1.55 \times 10^{14} \text{g / cm}^3$

7. Dec 26, 2017

Chronos

For enquiring minds, the current lightweight NS champion is reported here; https://arxiv.org/abs/1711.09804, Pulsar J1411+2551: A Low Mass New Double Neutron Star System. Whose companion weighs in at a scant .92 M ⊙. Must have taken quite the bang to produce a NS lighter than the smallest known white dwarf - reported here; https://arxiv.org/abs/1406.0488. A 1.05 M ⊙ Companion to PSR J2222-0137: The Coolest Known White Dwarf? Obviously we have work left to do on the EOS for degenerate stars. Things like this sometimes tempt me to reconsider how inflexible the laws of physics may actually be.

Last edited: Dec 26, 2017