Neutron Star Mergers: Probing the EoS of Hot, Dense Matter by Gravitational Waves

Abstract

Gravitational waves, electromagnetic radiation, and the emission of high energy particles probe the phase structure of the equation of state of dense matter produced at the crossroad of the closely related relativistic collisions of heavy ions and of binary neutron stars mergers. 3 + 1 dimensional special- and general relativistic hydrodynamic simulation studies reveal a unique window of opportunity to observe phase transitions in compressed baryon matter by laboratory based experiments and by astrophysical multimessenger observations. The astrophysical consequences of a hadron-quark phase transition in the interior of a compact star will be focused within this article. Especially with a future detection of the post-merger gravitational wave emission emanated from a binary neutron star merger event, it would be possible to explore the phase structure of quantum chromodynamics. The astrophysical observables of a hadron-quark phase transition in a single compact star system and binary hybrid star merger scenario will be summarized within this article. The FAIR facility at GSI Helmholtzzentrum allows one to study the universe in the laboratory, and several astrophysical signatures of the quark-gluon plasma have been found in relativistic collisions of heavy ions and will be explored in future experiments.

Bulk viscosity of baryonic matter with trapped neutrinos

“…In these events, a post-merger object is formed which either evolves into a stable neutron star or collapses to a black hole, once it cannot be supported by the differential rotation. As seen in numerical simulations [2][3][4][5][6][7][8][9][10][11][12][13][14][15] event of a merger leads to significant oscillations of the postmerger remnant, which can generate observable gravitational waves.…”

Equation of state for hot QCD and compact stars from a mean-field approach

“…Astrophysical observations of compact stars, along with data from the recent gravitational-wave detection by LIGO provide an additional tool to probe the equation of state of dense nuclear and possible quark matter [12][13][14][15][16][17][18] in the region of moderate temperatures and high baryon densities, close to those as created in HIC.…”

Hadron matter in neutron stars in view of gravitational wave observations

“…with the thermal part taken from the ideal gas law, P thermal = ρ M N k B T and ρ the rest mass density. Contributions due to relativistic particles ∝ T 4 and thermal corrections due to the nuclear part of order T 2 can be found in a very recent paper [137].…”

“…The resulting tidal deformability and mass-radius diagrams are as discussed in section 2. Figure 18: Snapshot of the density profile (left) and the temperature profile (right) about 6ms after the merger of two neutron stars, in a simulation reported in [137]. The temperature typically reaches several tens of MeV, here up to 50 MeV.…”

“…(The background color corresponds to a modeldependent assignment of quark fractions in the dense matter and is not discussed here). Reproduced from[137] under the Creative Com-mons 4.0 License. adiabatic index Γ in Eq.…”