Chandrasekhar Mass Limit of White Dwarfs in Modified Gravity

TL;DR

This study explores how modified gravity theories, specifically $f(R)$ models, affect the maximum mass and stability radius of white dwarfs, revealing that such theories predict lower stellar masses and larger minimal radii compared to General Relativity.

Contribution

The paper demonstrates that in $f(R)$ gravity models, white dwarf masses decrease and their minimal stable radii increase, providing new insights into stellar stability limits under modified gravity.

Findings

White dwarf mass decreases in $f(R)$ gravity models.

There exists a lower limit on the radius of stable white dwarfs.

Minimal radius of white dwarfs is larger than in General Relativity.

Abstract

We investigate the Chandrasekhar mass limit for white dwarfs in various models of $f(R)$ gravity. Two equations of state for stellar matter are used: simple relativistic polytropic equation with polytropic index $n=3$ and the realistic Chandrasekhar equation of state. For calculations it is convenient to use the equivalent scalar-tensor theory in the Einstein frame and then to return in the Jordan frame picture. For white dwarfs we can neglect terms containing relativistic effects from General Relativity and we consider the reduced system of equations. Its solution for any model of $f(R)=R+\beta R^{m}$ ($m\geq 2$, $\beta>0$) gravity leads to the conclusion that the stellar mass decreases in comparison with standard General Relativity. For realistic equations of state we find that there is a value of the central density for which the mass of white dwarf peaks. Therefore, in frames of modified gravity there is lower limit on the radius of stable white dwarfs and this minimal radius is greater than in General Relativity.