Implications for the supermassive black hole binaries from the NANOGrav 15-year data set

Several pulsar timing array (PTA) collaborations, including NANOGrav, EPTA, PPTA, and CPTA, have announced the evidence for a stochastic signal consistent with a stochastic gravitational wave background (SGWB). Supermassive black hole binaries (SMBHBs) are supposed to be the most promising gravitational-wave (GW) sources for this signal. In this paper, we use the NANOGrav 15-year data set to constrain the parameter space in an astro-informed formation model for SMBHBs. Our results prefer a large turn-over eccentricity of the SMBHB orbit when GWs begin to dominate the SMBHB evolution. Furthermore, the SGWB spectrum is extrapolated to the space-borne GW detector frequency band by including inspiral-merge-cutoff phases of SMBHBs, indicating that the SGWB from SMBHBs should be detected by LISA, Taiji and TianQin in the near future.

Automated summary

Several pulsar timing array collaborations have announced evidence for a stochastic signal consistent with a stochastic gravitational wave background, which is believed to come from supermassive black hole binaries. Using the NANOGrav 15-year data set, this paper constrains the parameter space in an astro-informed formation model for SMBHBs, showing a preference for a large turn-over eccentricity of the SMBHB orbit when gravitational waves dominate the SMBHB evolution. Furthermore, the study extrapolates the SGWB spectrum to the frequency band of space-borne GW detectors, indicating that the SGWB from SMBHBs should be detected by LISA, Taiji and TianQin in the near future.