What if GW190425 did not produce a black hole promptly?

TL;DR

This study uses numerical relativity simulations to explore whether GW190425 could have resulted in a long-lived neutron star remnant, examining implications for associated electromagnetic signals and constraining nuclear physics models.

Contribution

It provides the first detailed simulation-based analysis of GW190425's outcome, challenging the assumption of prompt black hole formation and assessing the potential for long-lived remnants.

Findings

A long-lived remnant is not ruled out by current constraints.

A stable remnant would produce a bright kilonova inconsistent with observations.

Radio signals from a long-lived remnant would be heavily absorbed, preventing FRB detection.

Abstract

It is widely believed that the binary neutron star merger GW190425 produced a black hole promptly upon merger. Motivated by the potential association with the fast radio burst FRB 20190425A, which took place 2.5~hours after the merger, we revisit the question of the outcome of GW190425 by means of numerical relativity simulations. We show that current laboratory and astrophysical constraints on the equation of state of dense matter do not rule out the formation of a long-lived remnant. However, the formation of a stable remnant would have produced a bright kilonova, in tension with upper limits by ZTF at the location and time of FRB 20190425A. Moreover, the ejecta would have been optically thick to radio emission for days to months, preventing a putative FRB from propagating out. The predicted dispersion measure is also several orders of magnitude larger than that observed for FRB 20190425A. Our results indicate that FRB 20190425A and GW190425 are not associated. However, we cannot completely rule out the formation of a long-lived remnant, due to the incomplete coverage of the relevant sky regions. More observations of GW190425-like events, including potential upper limit, have the potential to constrain nuclear physics. To this aim, it is important that follow-up observational campaigns of gravitational wave events are informed by the properties of the source, such as their chirp mass, and we urge the LIGO-Virgo-KAGRA collaboration to promptly release them publicly.