Signals of the QCD Phase Transition in the Heavens

TL;DR

This paper discusses how astrophysical observations of neutron stars and related phenomena can reveal signals of the QCD phase transition and exotic states of dense matter, complementing laboratory experiments.

Contribution

It highlights the potential of future astrophysical data to detect phase transitions and properties of dense QCD matter through signals like gravitational waves and spectral lines.

Findings

First order phase transitions can produce a third family of compact stars.

Quark matter microphysics affects r-mode stability in rotating stars.

Gravitational wave patterns can constrain the quark matter equation of state.

Abstract

The modern phase diagram of strongly interacting matter reveals a rich structure at high-densities due to phase transitions related to the chiral symmetry of quantum chromodynamics (QCD) and the phenomenon of color superconductivity. These exotic phases have significant impacts on high-density astrophysics as the properties of neutron stars and the evolution of astrophysical systems as proto-neutron stars, core-collapse supernovae and neutron star mergers. Most recent pulsar mass measurements and constraints on neutron star radii are critically discussed. Astrophysical signals for exotic matter and phase transitions in high-density matter proposed recently in the literature are outlined. A strong first order phase transition leads to the emergence of a third family of compact stars besides white dwarfs and neutron stars. The different microphysics of quark matter results in an enhanced r-mode stability window for rotating compact stars compared to normal neutron stars. Future telescope and satellite data will allow to extract signals from phase transitions in dense matter in the heavens and will reveal properties of the phases of dense QCD. Spectral line profiles out of x-ray bursts will determine the mass-radius ratio of compact stars. Gravitational wave patterns from collapsing neutron stars or neutron star mergers will even be able to constrain the stiffness of the quark matter equation of state. Future astrophysical data can therefore provide a crucial cross-check to the exploration of the QCD phase diagram with the heavy-ion program of the CBM detector at the FAIR facility.