Relativistic mergers of supermassive black holes and their electromagnetic signatures

Tanja Bode, Roland Haas, Tamara Bogdanović, Pablo Laguna, Deirdre Shoemaker

Research output: Contribution to journalArticlepeer-review


Coincident detections of electromagnetic (EM) and gravitational wave (GW) signatures from coalescence events of supermassive black holes (SMBHs) are the next observational grand challenge. Such detections will provide the means to study cosmological evolution and accretion processes associated with these gargantuan compact objects. More generally, the observations will enable testing general relativity in the strong, nonlinear regime and will provide independent cosmological measurements to high precision. Understanding the conditions under which coincidences of EM and GW signatures arise during SMBH mergers is therefore of paramount importance. As an essential step toward this goal, we present results from the first fully general relativistic, hydrodynamical study of the late inspiral and merger of equal-mass, spinning SMBH binaries in a gas cloud. We find that variable EM signatures correlated with GWs can arise in merging systems as a consequence of shocks and accretion combined with the effect of relativistic beaming. The most striking EM variability is observed for systems where spins are aligned with the orbital axis and where orbiting black holes form a stable set of density wakes, but all systems exhibit some characteristic signatures that can be utilized in searches for EM counterparts. In the case of the most massive binaries observable by the Laser Interferometer Space Antenna, calculated luminosities imply that they may be identified by EM searches to z 1, while lower mass systems and binaries immersed in low density ambient gas can only be detected in the local universe.

Original languageEnglish (US)
Pages (from-to)1117-1131
Number of pages15
JournalAstrophysical Journal
Issue number2
StatePublished - 2010
Externally publishedYes


  • Black hole physics
  • Galaxies: nuclei
  • Gravitational waves

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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