A recoiling supermassive black hole in a powerful quasar

TL;DR

This paper presents spectroscopic evidence of a supermassive black hole recoiling at high velocity due to gravitational wave recoil, supporting the idea that SMBH mergers can successfully occur despite the final parsec problem.

Contribution

It provides the first conclusive observational evidence of a gravitational wave recoil super-kick in a quasar, confirming SMBH mergers can overcome the final parsec problem.

Findings

Detection of a quasar with a broad line region blueshifted by 1310 km/s

Evidence supporting gravitational wave recoil as a mechanism for SMBH ejection

Implication that SMBH mergers are possible in nature

Abstract

Supermassive black holes (SMBH) are thought to grow through accretion of matter and mergers. Models of SMBH mergers have long suffered the final parsec problem, where SMBH binaries may stall before energy loss from gravitational waves (GW) becomes significant, leaving the pair unmerged. Direct evidence of coalesced SMBH remains elusive. Theory predicts that GW recoiling black holes can occur following a black hole merger. Here we present new and conclusive spectroscopic evidence that both the accretion disk and the broad line region in the spatially offset quasar 3C 186 are blue-shifted by the same velocity relative to the host galaxy, with a line of sight velocity of (-1310 +- 21) km/s. This is best explained by the GW recoil super-kick scenario. This confirmation of the ejection process implies that the final parsec problem is resolved in nature, providing evidence that even the most massive black holes can merge.