Neutron Star Radii

 

There have been been a growing number of radius measurements of neutron stars with modern X-ray instruments in the past few years.  Recent studies have also included a careful assessment of the statistical and systematic uncertainties in such measurements. The most reliable and constraining radius measurements to date have come from neutron stars in binaries with low-mass companions. There are by now fourteen of these: six neutron stars that show repeated thermonuclear bursts and eight neutron stars during quiescence. The diagrams below show the most up-to-date mass-radius likelihoods for these sources.

 

You can find the mass-radius likelihoods for all of these measurements in one tar file here.

 

radii1

 

 

Constraints on the neutron star equation of state and the most likely mass-radius relation are obtained by combining these astrophysical measurements of the radii with the results of nuclear physics experiments at low densities and the requirement that the maximum mass in a mass-radius relation reach ~2 Msun. The most likely mass-radius relation that is derived from the current data and its 2-sigma uncertainties are shown in the figure below.

 

MR_constraints

References:
Ozel et al. 2016, ApJ, in press (arXiv:1505.05155)
Bogdanov et al. 2016, ApJ, submitted
Ozel & Freire 2016, Annual Reviews of Astronomy and Astrophysics