Is GW190425 consistent with being a neutron star$-$black hole merger?

Abstract

GW190425 is the second neutron star merger event detected by the Advanced LIGO/Virgo detectors. If interpreted as a double neutron star merger, the total gravitational mass is substantially larger than that of the binary systems identified in the Galaxy. In this work we analyze the gravitational-wave data within the neutron star$-$black hole merger scenario. For the black hole, we yield a mass of $2.40_{-0.32}^{+0.36}{M}_{\odot }$ and an aligned spin of $0.141_{-0.064}^{+0.067}$. As for the neutron star we find a mass of $1.15_{-0.13}^{+0.15}{M}_{\odot }$ and the dimensionless tidal deformability of $1.4_{-1.2}^{+3.8}\times 10^3$. These parameter ranges are for 90\% credibility. The inferred masses of the neutron star and the black hole are not in tension with current observations and we suggest that GW190425 is a viable candidate of a neutron star$-$black hole merger event. Benefitting from the continual enhancement of the sensitivities of the advanced gravitational detectors and the increase of the number of the observatories, similar events are anticipated to be much more precisely measured in the future and the presence of black holes below the so-called mass gap will be unambiguously clarified. If confirmed, the mergers of neutron stars with (quickly rotating) low-mass black holes are likely important production sites of the heaviest r-process elements.

7 pages, 4 figures, ApJL published

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• Distinguishing double neutron star from neutron star-black hole binary populations with gravitational wave observations
• A correlation between Ha trough depth and inclination in quiescent X-ray transients: evidence for a low-mass black hole in GRO J0422+32
• Breaking of universal relationships of axial wI-modes in hybrid stars: rapid and slow hadron-quark conversion scenarios
• Constraints on the dense matter equation of state and neutron star properties from NICER's mass-radius estimate of PSR J0740+6620 and multimessenger observations
• Population Synthesis of Black Hole Binaries with Compact Star Companions
• A Common Origin for Low Mass Ratio Events Observed by LIGO and Virgo in the First Half of the Third Observing Run