On the existence of ergoregions in rotating stars.
Abstract
An ergoregion (ER) is defined as a region around a collapsed rotating star where all particle and photon orbits are forced to corotate with the star. An approximate method for determining the existence and structure of an ER is presented which involves calculation of the structure of a nonrotating star and subsequent integration of the equation for the 'dragging of inertial frames' in the slowrotation approximation. Numerical results are evaluated for nonrotating stars of uniform density and for the degenerateneutron equation of state of Harrison et al. (1965). Consideration of rigidly rotating neutron stars indicates that no such star with a realistic equation of state is likely to develop an ER; it is also suggested that differential rotation is unlikely to be much more effective in forming ERs. Results are summarized for a calculation of the growth rate of Friedman's (1975) ER instability for the case of a massless scalar field. It is concluded that ERs could conceivably arise in the presence of ultrastiff and ultradense equations of state.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 January 1978
 DOI:
 10.1093/mnras/182.1.69
 Bibcode:
 1978MNRAS.182...69S
 Keywords:

 Neutron Stars;
 Stellar Models;
 Stellar Rotation;
 Astronomical Models;
 Cosmology;
 Equations Of State;
 Stellar Structure;
 Astrophysics;
 Neutron Stars:Rotation;
 Relativistic Stars:Rotation;
 Relativistic Stars: Stability