The NANOGrav 15-year Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational Wave Background

• DOI: 10.3204/pubdb-2023-07501
• Publication Date: 2023-08-01
• Authors: Agazie, Gabriella; Anumarlapudi, Akash; Archibald, Anne M.; Baker, Paul T.; Bécsy, Bence; Blecha, Laura; Bonilla, Alexander; Brazier, Adam; Brook, Paul R.; Burke-Spolaor, Sarah; Burnette, Rand; Case, Robin; Casey-Clyde, J. A...; Charisi, Maria; Chatterjee, Shami; Chatziioannou, Ka...; Cheeseboro, Belin...; Chen, Siyuan; Cohen, Tyler; Cordes, James M.; Cornish, Neil J.; Crawford, Fronefield; Cromartie, H. Tha...; Crowter, Kathryn; Cutler, Curt J.; D’Orazio, Daniel J.; DeCesar, Megan E.; DeGan, Dallas; Demorest, Paul B.; Deng, Heling; Dolch, Timothy; Drachler, Brendan; Ferrara, Elizabet...; Fiore, William; Fonseca, Emmanuel; Freedman, Gabriel E.; Gardiner, Emiko; Garver-Daniels, Nate; Gentile, Peter A.; Gersbach, Kyle A.; Glaser, Joseph; Good, Deborah C.; Gültekin, Kayhan; Hazboun, Jeffrey S.; Hourihane, Sophie; Islo, Kristina; Jennings, Ross J.; Johnson, Aaron; Jones, Megan L.; Kaiser, Andrew R.; Kaplan, David L.; Kelley, Luke Zoltan; Kerr, Matthew; Key, Joey S.; Laal, Nima; Lam, Michael T.; Lamb, William G.; W. Lazio, T. Joseph; Lewandowska, Natalia; Littenberg, Tyson B.; Liu, Tingting; Luo, Jing; Lynch, Ryan S.; Ma, Chung-Pei; Madison, Dustin R.; McEwen, Alexander; McKee, James W.; McLaughlin, Maura A.; McMann, Natasha; Meyers, Bradley W.; Meyers, Patrick M.; Mingarelli, Chiar...; Mitridate, Andrea; Natarajan, Priyam...; Ng, Cherry; Nice, David J.; Ocker, Stella Koch; Olum, Ken D.; Pennucci, Timothy T.; Perera, Benetge B...; Petrov, Polina; Pol, Nihan S.; Radovan, Henri A.; Ransom, Scott M.; Ray, Paul S.; Romano, Joseph D.; Runnoe, Jessie C.; Sardesai, Shashwa...; Schmiedekamp, Ann; Schmiedekamp, Carl; Schmitz, Kai; Schult, Levi; Shapiro-Albert, B...; Siemens, Xavier; Simon, Joseph; Siwek, Magdalena S.; Stairs, Ingrid H.; Stinebring, Danie...; Stovall, Kevin; Sun, Jerry P.; Susobhanan, Abhim...; Swiggum, Joseph K.; Taylor, Jacob; Taylor, Stephen R.; Turner, Jacob E.; Unal, Caner; Vallisneri, Michele; Vigeland, Sarah J.; Wachter, Jeremy M.; Wahl, Haley M.; Wang, Qiaohong; Witt, Caitlin A.; Wright, David; Young, Olivia; NANOGrav Collabor...
• Keywords: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Population; FOS: Physical sciences; General Relativity and Quantum Cosmology (gr-qc); Astrophysics; 530; Astrophysical Studies of Black Holes; Amplitude; Quantum mechanics; General Relativity and Quantum Cosmology; Gravitational waves; Sociology; Galaxy evolution; Supermassive black holes; Supermassive black hole; FOS: Mathematics; Observation and Study of Gravitational Waves Phenomenon; Binary Black Hole; Demography; Gravitational Waves; High Energy Astrophysical Phenomena (astro-ph.HE); Arithmetic; Galaxy Formation and Evolution in the Universe; Physics; Gravitational wave background; Astronomy and Astrophysics; 520; FOS: Sociology; QB460-466; Galaxy; Physics and Astronomy; Physical Sciences; Astrophysics - High Energy Astrophysical Phenomena; Binary number; info:eu-repo/classification/ddc/520; Gravitational wave; Mathematics; Astrophysics - Cosmology and Nongalactic Astrophysics

Abstract The NANOGrav 15 yr data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such low-frequency gravitational waves, here we analyze the signal as coming from a population of supermassive black hole (SMBH) binaries distributed throughout the Universe. We show that astrophysically motivated models of SMBH binary populations are able to reproduce both the amplitude and shape of the observed low-frequency gravitational-wave spectrum. While multiple model variations are able to reproduce the GWB spectrum at our current measurement precision, our results highlight the importance of accurately modeling binary evolution for producing realistic GWB spectra. Additionally, while reasonable parameters are able to reproduce the 15 yr observations, the implied GWB amplitude necessitates either a large number of parameters to be at the edges of expected values or a small number of parameters to be notably different from standard expectations. While we are not yet able to definitively establish the origin of the inferred GWB signal, the consistency of the signal with astrophysical expectations offers a tantalizing prospect for confirming that SMBH binaries are able to form, reach subparsec separations, and eventually coalesce. As the significance grows over time, higher-order features of the GWB spectrum will definitively determine the nature of the GWB and allow for novel constraints on SMBH populations.