Implications for the Supermassive Black Hole Binaries from the NANOGrav 15-year Data Set

TL;DR

This paper uses the NANOGrav 15-year data to constrain the gravitational wave background from supermassive black hole binaries, suggesting high orbital eccentricities and predicting detections by future space-based GW observatories.

Contribution

It introduces an astro-informed model to interpret the NANOGrav data, highlighting the importance of orbital eccentricity and providing extrapolations for future GW detector observations.

Findings

Preference for large turn-over eccentricity in SMBHBs

GWB spectrum extrapolated to space-based GW detectors

Predicted detection by LISA, Taiji, and TianQin

Abstract

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