Observational constraints on spinning, relativistic Bose-Einstein condensate stars

TL;DR

This paper investigates whether spinning relativistic Bose-Einstein condensate stars can match observed neutron star properties, concluding that such stars cannot simultaneously fit observed mass and radius constraints despite EOS flexibility.

Contribution

It demonstrates that spinning relativistic BEC stars with the CSW EOS cannot simultaneously match observed neutron star masses and radii, challenging their candidacy as realistic models.

Findings

BEC stars can reach high masses but not small enough radii

The CSW EOS cannot produce stars matching recent observational constraints

The conclusion applies broadly to any spinning boson star obeying the CSW EOS

Abstract

Bose-Einstein condensates (BECs) have been proposed as candidate states of matter for the interior of neutron stars. Specifically, Chavanis and Harko obtained the mass-radius relation for a BEC star and proposed that the recently discovered neutron stars with masses around 2$M_\odot$ are BEC stars. They employed a barotropic equation of state (EOS), with one free parameter, that was first found by Colpi, Wasserman, and Shapiro (CSW), to describe them and derive stable equilibrium configurations of spinning BEC stars in General Relativity. In this work we show that while it is true that BECs allow for compact object masses as heavy as the heaviest observed ones, such stars cannot simultaneously have radii that are small enough to be consistent with the latest observations, in spite of the flexibility available in the EOS in the form of the free parameter. In fact, our conclusion applies to any spinning relativistic boson star that obeys the CSW EOS.