What is the minimum mass of a neutron star?

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Discussion Overview

The discussion revolves around the minimum mass of neutron stars, exploring theoretical limits, observed masses, and the implications of recent discoveries related to neutron star mergers. Participants examine the relationship between neutron stars and white dwarfs, as well as the uncertainties surrounding mass limits.

Discussion Character

  • Exploratory, Debate/contested, Technical explanation

Main Points Raised

  • Some participants reference the Chandrasekhar Limit of approximately 1.4 solar masses as a potential minimum for neutron stars, but express uncertainty about whether neutron stars can exist below this mass.
  • Others mention observed neutron stars with masses as low as 1.1 or 1.2 solar masses, suggesting that the minimum mass may be lower than previously thought.
  • One participant cites the pulsar PSR J0453+1559 as the least massive observed neutron star at 1.174 ± 0.004 M⊙, indicating that there are neutron stars below the Chandrasekhar Limit.
  • Calculations by Oppenheimer and Volkoff suggest a theoretical mass range for neutron stars between 0.7 and 3.0 M⊙, but participants note that different assumptions lead to varying mass limits.
  • There is mention of a recent neutron star merger event that has established an upper mass limit of approximately 2.16 solar masses, but participants clarify that this does not directly inform the lower mass limit.
  • Some participants argue that the observed mass range may not accurately represent the true minimum mass due to the complexities involved in supernova events and the formation of neutron stars.
  • Concerns are raised about the reliability of studies establishing mass limits, with some participants noting that there is still significant uncertainty in the values presented.

Areas of Agreement / Disagreement

Participants express a range of views regarding the minimum mass of neutron stars, with no consensus reached. There are competing hypotheses about the relationship between neutron stars and white dwarfs, as well as differing interpretations of recent findings.

Contextual Notes

There are unresolved questions regarding the assumptions made in various calculations of neutron star mass limits, and the dependence on definitions of mass categories (e.g., neutron stars vs. white dwarfs) complicates the discussion.

  • #31
PeterDonis said:
I don't have my copy of Shapiro & Teukolsky handy

I do. They give 0.18 solar masses under Harrison-Wheeler EOS. The Oppenheimer and Volkoff EOS has no lower bound. The reason they don't spring back to white dwarfs is, as you say, that this requires work, and the energy to do that work has already left the system.
 
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  • #32
I've found this paper which probably meets my needs:

https://iopscience.iop.org/article/10.1088/0004-637X/778/1/66
Equation (3) gives a range at formation for an isolated NS as:

M_birth∼1.08–1.57M_☉

Presumably a star exceeding the Chandrasekhar limit would start to collapse but the implosion of the core could eject some surface material to leave a remnant slightly below the limit.

In binary systems, mass transfer raises the mass of the first NS formed as the companion sheds so they have a different distribution with a higher mean (see figure 2) but I don't see any way the mass could be reduced significantly after formation.
 
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