APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022;
New York
Session D15: Gravitational Wave Sources and Populations
1:30 PM–3:06 PM,
Saturday, April 9, 2022
Room: Soho
Sponsoring
Units:
DAP DGRAV
Chair: Colm Talbot, Massachusetts Institute of Technology
Abstract: D15.00003 : Inferring the Neutron Star Maximum Mass and Lower Mass Gap in Neutron Star–Black Hole Systems with Spin
1:54 PM–2:06 PM
Abstract
Presenter:
Christine Ye
(Eastlake High School)
Authors:
Christine Ye
(Eastlake High School)
Maya Fishbach
(Northwestern University)
Gravitational-wave (GW) detections of merging neutron star--black hole (NSBH) systems provide a new way to probe the astrophysical neutron star (NS) and black hole (BH) mass distributions, especially at the transition between NS and BH masses. Of particular interest are the maximum NS mass, which probes the mysterious nature of high-density nuclear matter, and a potential mass gap between the maximum NS mass and the minimum BH mass, which probes probes the uncertain supernova explosion mechanism. Previous GW measurements of the NS mass distribution have assumed nonspinning NSs; however, rapidly spinning NSs, if they exist, can extend to larger maximum masses and may appear to fill in the mass gap. This is particularly relevant in light of the recent GW detection of either the most massive NS or the lightest BH -- a 2.6 solar mass object in the event GW190814 -- which several authors have proposed is a rapidly spinning NS. In this work, we explore whether the spin-dependent NS maximum mass and the lower mass gap can be inferred in spinning NSBH systems. We jointly model the NS spin distribution and the NSBH mass distribution, and apply the inference to four LIGO--Virgo NSBH detections and simulated future GW data. We find that current NSBH events support a mass gap, although GW190814's nature remains unclear. Both the mass gap width and NS maximum mass vary with spin assumptions; in particular, estimates of the maximum mass when including or excluding GW190814 differ, but this tension is partially resolved if GW190814 is assumed to have significant spin. Under simplified assumptions, 150 future NSBH events may constrain the maximum nonspinning NS mass to $\pm0.02\,M_\odot$, and we may even measure the relation between the NS maximum mass and NS spin entirely from GW data. We show that if rapidly rotating NSs exist, the NS spin and mass distributions must be modeled simultaneously to avoid biasing inference of the NS maximum mass.