The Gravitational Redshift of Rotating Neutron Stars

Paul Nunez
U of  Sergio Arboleda (Bogota, Colombia)

When a spherically symmetric space-time is used to describe the exterior field of a compact object, the measurement of the gravitational redshift can be used to extract macroscopic properties such as the compactness (M/R) of the star. However, when rotation is taken into account, it is shown that the  gravitational redshift is altered and the compactness parameter is no longer unique. Nevertheless, useful information on the radius can still be extracted even in the presence of rotation. A closer analysis also shows that by measuring the gravitational redshift, one can infer the maximum angular velocity of the star. The periods corresponding to this maximum angular velocity are of milliseconds, typically found in millisecond pulsars, suggesting that these objects are reaching their rotational limit.