Extracting Information from the Gravitational Redshift of Compact Rotating Objects

TL;DR

This paper explores how gravitational redshift measurements, combined with theoretical insights, can reveal properties like radius and maximum rotation speed of compact rotating objects such as pulsars and neutron stars.

Contribution

It introduces a method to extract information on the radii and maximum angular velocities of rotating compact objects using gravitational redshift data and theoretical constraints.

Findings

Millisecond periods are a semi-theoretical limit based on General Relativity.

Gravitational redshift can provide information on compactness despite rotation effects.

Method applied to pulsars, white dwarfs, and neutron stars.

Abstract

When rotation is not taken into account, the measurement of the Gravitational Redshift can provide unique information about the compactness ($M/R$) of the star. Rotation alters the gravitational redshift rendering thereby a unique determination of the compactness parameter impossible. Nevertheless, it can be shown that by using some theoretical input, useful information on, say, the radii of compact rotating objects can still be extracted. Moreover, by measuring the gravitational redshift one can infer the maximum angular velocity of the object. As it is well known, the minimum observed periods of rotation are found in millisecond pulsars. Here we show that millisecond periods are actually a semi-theoretical limit that can be found by General Relativistic arguments corresponding to the maximum angular velocity. We apply our method to compact objects such as pulsars, white dwarfs and neutron stars.