Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars

Understand

The innermost stable cicular orbit (ISCO) of an accretion disc orbiting a neutron star (NS) is often assumed a unique prediction of general relativity.

• However, it has been argued that ISCO also appears around highly elliptic bodies described by Newtonian theory.
• In this sense, the behaviour of an ISCO around a rotating oblate neutron star is formed by the interplay between relativistic and Newtonian effects.
• Here we briefly explore the consequences of this interplay using a straightforward analytic approach as well as numerical models that involve modern NS equations of state.