Signatures of recoiled supermassive black holes

• Applicant: Professor Dr. Pavel Kroupa, since 7/2010
• Subject Area: Astrophysics and Astronomy
• Term: from 2007 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 42513258

The simulation of binary black holes to full coalescence has recently become possible thanks to the breakthroughs in numerical relativity. In contrast with early theoretical predictions, the simulations have shown that the merger of a black hole binary due to emission of gravitational waves results in a kick velocity imparted to the remnant black hole. The amplitude of such a kick velocity depends on the properties of the binary at the time of inspiral and ranges from a few hundred km/s to a few thousands km/s for the most favorable configurations. Such kicks can be large enough to displace the black hole from the center of its host galaxy or even to eject it altogether, producing isolated black holes in intergalactic space.These astounding results may require us to revise existing models of galaxy formation and evolution. Gravitational-wave recoils can have major implications on the evolution of galaxies, which is strongly linked to the properties of central black holes. We therefore propose to investigate the consequences of black hole recoils and recognize possible observational signatures that can help to identify real candidates. The most promising observational feature is the existence of compact star clusters around recoiling black holes, formed by the bound stars that the black hole carries along while it escapes. Such clusters are expected to have physical properties different from all known classes of compact systems, such as small sizes, high internal velocity dispersions, high mass-to-light ratios, broad-band colors and high space velocities.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1177: Witnesses of Cosmic History: Formation and Evolution of Black Holes, Galaxies and Their Environments
• Ehemaliger Antragsteller: Professor Dr. Holger Baumgardt, until 7/2010