Universal Relations for Innermost Stable Circular Orbits around Rapidly Rotating Neutron Stars

  title={Universal Relations for Innermost Stable Circular Orbits around Rapidly Rotating Neutron Stars},
  author={Shun-Sun Luk and L. Lin},
  journal={The Astrophysical Journal},
We study the innermost stable circular orbit (ISCO) of a test particle around rapidly rotating neutron stars. Based on 12 different nuclear-matter equations of state (EOS), we find numerically two approximately EOS-insensitive universal relations that connect the radius and orbital frequency of the ISCO to the spin frequency f and mass M of rotating neutron stars. The relations are EOS-insensitive to about the 2% level for a large range of Mf. We also find that the universal relation for the… Expand
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