Hydrodynamics of Relativistic Superheated Bubbles

TL;DR

This paper investigates the hydrodynamics of relativistic, charged superheated bubbles potentially relevant in neutron star mergers, highlighting unique pressure behaviors, flow patterns, and implications for gravitational wave signals.

Contribution

It provides a detailed analysis of superheated bubble hydrodynamics in relativistic regimes, including effects of conserved charges and implications for gravitational wave production.

Findings

Pressure at bubble center can be higher or lower than surrounding phase.

Metastable regions can develop behind the bubble wall.

Efficiency factor for gravitational wave emission is computed.

Abstract

Relativistic, charged, superheated bubbles may play an important role in neutron star mergers if first-order phase transitions are present in the phase diagram of Quantum Chromodynamics. We describe the properties of these bubbles in the hydrodynamic regime. We find two qualitative differences with supercooled bubbles. First, the pressure at the center of an expanding superheated bubble can be higher or lower than the pressure in the asymptotic, metastable phase. Second, some fluid flows develop metastable regions behind the bubble wall for any choice of the equation of state. We consider the possible role of a conserved charge akin to baryon number. The fluid flow profiles are unaffected by this charge if the speed of sound is constant in each phase, but they are modified for more general equations of state. We compute the efficiency factor relevant for gravitational wave production.