Neutron Star Masses


An up-to-date compilation of neutron star mass measurements in various source categories. You can download the data for this figure from here or find the pdf version of the data tables here.



Reference: Ozel & Freire 2016, Annual Reviews of Astronomy and Astrophysics



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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.





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.



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


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Dense Matter EoS


The composition and interactions of matter above nuclear saturation density still pose a great challenge to nuclear physics. We show  in the figure below a large number of proposed EoS, including nucleonic and quark EoS, mean-field models, and those including hyperons and condensates.


Here are the links to a tar file with these EoS in tabular form and a tar file for the corresponding mass-radius relations. You can find README files in both folders with descriptions of the tables and the references for each EoS.




Astrophysical observations of neutron star radii and masses, combined with the constraints from low density nuclear physics experiments provide tight constraints on the dense matter EoS. The empirically determined region that is in agreement with all current constraints is shown in blue.



Earlier compilations and naming conventions are from Lattimer & Prakash 2001 and Read et al. 2009. The full list included above is from Ozel & Freire 2016.



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