Speaker
Description
The nature of the compact objects within the supposed 3-5M⊙ “lower mass gap” remains uncertain. Observations of GW190814 and GW230529 highlight the challenges gravitational waves face in distinguishing neutron stars from black holes. Interpreting these systems is especially difficult because classifications depend simultaneously on measurement noise, compact binary population models, and equation of state (EOS) constraints on the maximum neutron star mass. We analyze 66 confident events from GWTC-3 to quantify how the probability of a component being a neutron star, P(NS), varies across the population. The effects are substantial: the data reveals that P(NS) varies between 1% – 62% for GW230529’s primary and P(NS) ranges 39% – 99% for GW190425’s primary. By contrast, the asymmetric GW190814’s secondary varies P(NS) by ≤ 10%, demonstrating robustness at high SNR. Across our analysis, the dominant drivers of classification are the pairing preferences of neutron stars with other compact objects, and the neutron star spin distributions. Analysis using EOS information tends to affect P(NS) through the inferred maximum neutron star mass rather than the maximum spin. Without a systematic treatment of the numerous parameters influencing P(NS), its proposed role as a robust astrophysical observable is unlikely to withstand scrutiny, which may lead to ambiguous classifications of future GW events.
