# High-mass twin stars with a multi-polytrope EoS

## TL;DR

This paper demonstrates that a three-polytrope model of neutron star equations of state can produce high-mass twin stars with similar masses but different radii, and discusses constraints on their maximum mass.

## Contribution

It introduces a multi-polytrope approach to model neutron star EoS, confirming the existence of high-mass twin stars and analyzing the impact of causality constraints.

## Key findings

- High-mass twin stars with ~2 solar masses and different radii are possible.
- Causality constraints limit the maximum mass of the third family of stars.
- Extending to four polytropes relaxes these constraints, mimicking realistic EoS.

## Abstract

We show that in the 3-polytropes model of Hebeler et al. \cite{Hebeler:2013nza} for the neutron star equation of state at supersaturation densities a third family of compact stars can be obtained which confirms the possibility of high-mass twin stars that have coincident masses $M_1=M_2\approx 2~M_\odot$ and significantly different radii $|R_1-R_2|>2-3 $ km. We show that the causality constraint puts severe limitations on the maximum mass of the third family sequence which can be relaxed when this scheme is extended to four polytropes thus mimicking a realistic high-density matter EoS.