Gravitational Wave Signal for Quark Matter with Realistic Phase Transition

Abstract

The cores of neutron stars (NSs) near the maximum mass realize the most highly compressed matter in the universe where quark degrees of freedom may be liberated. Such a state of dense matter is hypothesized as quark matter (QM) and its presence has awaited to be confirmed for decades in nuclear physics. Gravitational waves from binary NS mergers are expected to convey useful information called the equation of state (EOS). However, the signature for QM with realistic EOS is not yet established.Here, we show that the gravitational wave in the post-merger stage can distinguish the theory scenarios with and without a transition to QM. Instead of adopting specific EOSs as studied previously, we compile reliable EOS constraints from the ab initio approaches. We demonstrate that early collapse to a black hole after NS merger signifies softening of the EOS associated with the onset of QM in accord with ab initio constraints. Nature of hadron-quark phase transition can be further constrained by the condition that electromagnetic counterparts need to be energized by the material left outside the remnant black hole.

Kilohertz Gravitational Waves from Binary Neutron Star Mergers: Inference of Postmerger Signals with the Einstein Telescope

“…Another quantity that encodes the softening of the EOS at high densities is the time of BH collapse t coll . A softer EOS allows the NS remnant to reach higher densities, yielding to an earlier BH collapse for comparable masses [22,29,39]. The recovered posteriors at SNR 8 for t coll give t coll = 28 +36 −24 ms for DD2 and t coll = 6 +41 −4 ms for BHBΛφ, consistently with the injected values.…”

“…For example, several NR simulations indicate that deviations of the orders of ∼500 Hz in the f 2 peak and of ∼20 ms in the time of BH collapse are possible due EOS softening, [e.g. 22,29,39,42,43]. We considered a short-lived remnant as a case study and demonstrate that ∼3−σ violations of EOS-insensitive relations are potentially observable at PM SNR 8.…”

“…In general, more accurate studies of BNS merger with non-nucleonic EOS, driven by high-precision NR simulations [e.g. 22,29,39], are essential in order to comprehensively characterize to what extend the breaking of EOS-insensitive relations can probe EOS softening.…”

Kilohertz Gravitational Waves From Binary Neutron Star Mergers: Numerical-relativity Informed Postmerger Model

“…Hence, the observational imprint of EOS softening might be better revealed from an earlier BH collapse phenomenology, e.g. [16,25,84,119,120], rather than from the mea-surement of PM frequencies (under the assumption that our sample of models adequately represent the "true" EOS). However, the cases BHBΛφ 1.50+1.50 M , BLQ 1.40+1.40 M 7 and other literature results [26,121,122] suggest that the EOS-insentive relations for M f 2 (κ T 2 ) (and in principle for other quantities) might break for particular binary masses and in presence of "strong" phase transitions 8 .…”

“…[81][82][83]. The time of collapse t coll is difficult to robustly determine from simulations due its dependence on grid resolution [11]; moreover, it strongly depends on the properties of the nuclear EOS and might be biased by the relatively small EOS set available [16,25,84]. The frequency drift α peak is also connected to the collapse dynamics and, as such, it can be affected by various processes, especially in long-lived remnants.…”