Buchdahl-Bondi limit in modified gravity: Packing extra effective mass in relativistic compact stars

TL;DR

This paper extends the Buchdahl-Bondi limit within f(R) gravity, showing that stable, more massive stars with higher surface redshift can exist, offering new tests for gravity theories and potential dark matter explanations.

Contribution

It generalizes the Buchdahl-Bondi limit to f(R) gravity, demonstrating the possibility of stable, extra-massive stars with higher redshift, independent of specific stellar models.

Findings

Stable stars with surface redshift > 2 are possible in f(R) gravity.

The limit for maximum mass of compact stars is higher than in general relativity.

Provides observational tests to distinguish between f(R) gravity and general relativity.

Abstract

We generalise the Buchdahl-Bondi limit for the case of static, spherically symmetric, relativistic compact stars immersed in Schwarzschild vacuum in f(R)-theory of gravity, subject to very generic regularity, thermodynamic stability and matching conditions. Similar to the case of general relativity, our result is model independent and remains true for any physically realistic equation of state of standard stellar matter. We show that an extra-massive stable star can exist in these theories, with surface redshift larger than 2, which is forbidden in general relativity. This result gives a novel and interesting observational test for validity or otherwise of general relativity and also provides a possible solution to the dark matter problem.