2024/11/05 by Albert Sneppen, Sneppen, Albert, Oliver Just +21 · 2 citations
Earth and Planetary Sciences · Physics and Astronomy · #FOS: Physical sciences #Geophysics and Gravity Measurements #High Energy Astrophysical Phenomena (astro-ph.HE) #Nuclear Theory (nucl-th) #Pulsars and Gravitational Waves Research #Solar and Space Plasma Dynamics
paper · pdf · doi:10.48550/arxiv.2411.03427
openalex publication_date 2024/11/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
The time until black hole formation in a binary neutron-star (NS) merger contains invaluable information about the nuclear equation of state (EoS) but has thus far been difficult to measure. We propose a new way to constrain the merger remnant's NS lifetime, which is based on the tendency of the NS remnant neutrino-driven winds to enrich the ejected material with helium. Based on the He I λ1083.3 nm line, we show that the feature around 800-1200 nm in AT2017gfo at 4.4 days seems inconsistent with a helium mass fraction of XHe \gtrsim 0.05 in the polar ejecta. Our recent neutrino-hydrodynamic simulations of merger remnants are only compatible with this limit if the NS remnant collapses within 20-30 ms. Such a short lifetime implies that the total binary mass of GW170817, M_\rm tot, lay close to the threshold binary mass for direct gravitational collapse, Mthres, for which we estimate Mthres\lesssim 2.93 M_\odot. This upper bound on Mthres yields upper limits on the radii and maximum mass of cold, non-rotating NSs, which rule out simultaneously large values for both quantities. In combination with causality arguments, this result implies a maximum NS mass of Mmax\lesssim2.3 M_\odot. The combination of all limits constrains the radii of 1.6 M_\odot NSs to about 12±1 km for Mmax = 2.0 M_\odot and 11.5±1 km for Mmax = 2.15 M_\odot. This ∼2 km allowable range then tightens significantly for Mmax above ≈2.15 M_\odot. This rules out a significant number of current EoS models. The short NS lifetime also implies that a black-hole torus, not a highly magnetized NS, was the central engine powering the relativistic jet of GRB170817A. Our work motivates future developments... [abridged]