Observation of Gravitational Waves from the Coalescence of a $2.5\text{-}4.5~M_\odot$ Compact Object and a Neutron Star

• Main Authors: Agathos, M, Aronson, S. M, Belardinelli, D, Bentara, I, Bentley, J. D, Bersanetti, D, Boudon, A, Bryant, J, Callister, T. A, Chatterjee, Debarati, Chen, H. Y, Chierici, R, Craig, K, Criswell, A. W, Datta, S, Dattilo, V, De Laurentis, M, Dohmen, E, Dooney, T, Edo, T. B, Favaro, G, Fenyvesi, E, Fleischer, S. M, Foley, E. M, Forsyth, P. W. F, Frolov, V. V, Gergely, L, Giri, P, Green, S. M, Guerra, D, Guo, H, Hough, J, Hu, Q, Huang, H. Y, Imafuku, H, Itoh, Y, Juste, V, Kanner, J. B, Khanam, T, Kimball, C, Knust, N, Koekoek, G, Lin, C-Y, Lin, H, Lumaca, D, McCuller, L, Mobilia, L, Moraru, D, Moriwaki, Y, Murray, P. G, Narayan, P, Narikawa, T, Ossokine, S, Panther, F. H, Paolone, A, Passaquieti, R, Patra, A, Patricelli, B, Penn, S, Périgois, C, Perreca, A, Pinard, L, Piotrzkowski, B. J, Placidi, E, Quinonez, P. J, Relton, P, Renzini, A. I, Rezaei, A. S, Romano, R, Rossello, M, Saha, S. S, Saleem, M, Schouteden, K, Scialpi, M, Shao, L, Sharma, A. K, Shinkai, H, Singh, S, Sintes, A. M, Song, I, Sordini, V, Sotani, H, Suchenek, M, Szewczyk, P, Tripathee, A, Troiano, L, Trudeau, R. J, Vajpeyi, A, Veitch, J, Viets, A. D, Vincent, E. T, Vocca, H, Was, M, Wellmann, F, Wright, J. L, Wu, C, Yamamoto, H, Yamazaki, R, Zhang, A. C, Zucker, M. E
• Format: Journal Article
• Language: English
• Published: 05.04.2024
• Subjects: Physics - General Relativity and Quantum Cosmology; Physics - High Energy Astrophysical Phenomena
• DOI: 10.48550/arxiv.2404.04248

ApJL 970, L34 (2024) We report the observation of a coalescing compact binary with component masses $2.5\text{-}4.5~M_\odot$ and $1.2\text{-}2.0~M_\odot$ (all measurements quoted at the 90% credible level). The gravitational-wave signal GW230529_181500 was observed during the fourth observing run of the LIGO-Virgo-KAGRA detector network on 2023 May 29 by the LIGO Livingston Observatory. The primary component of the source has a mass less than $5~M_\odot$ at 99% credibility. We cannot definitively determine from gravitational-wave data alone whether either component of the source is a neutron star or a black hole. However, given existing estimates of the maximum neutron star mass, we find the most probable interpretation of the source to be the coalescence of a neutron star with a black hole that has a mass between the most massive neutron stars and the least massive black holes observed in the Galaxy. We provisionally estimate a merger rate density of $55^{+127}_{-47}~\text{Gpc}^{-3}\,\text{yr}^{-1}$ for compact binary coalescences with properties similar to the source of GW230529_181500; assuming that the source is a neutron star-black hole merger, GW230529_181500-like sources constitute about 60% of the total merger rate inferred for neutron star-black hole coalescences. The discovery of this system implies an increase in the expected rate of neutron star-black hole mergers with electromagnetic counterparts and provides further evidence for compact objects existing within the purported lower mass gap.