Statistics of Stars with Relativistic Velocities

The scenario for the dynamical capture of a binary system in the neighborhood of a supermassive black hole used byHills in 1988 to predict the existence of hypervelocity stars (~1000 km/s) allows the existence of stars with relativistic velocities attaining (1/3?2/3)c, where c is the speed of light. The increase of the kinetic energy of these stars by more than a factor of 100 is due to the replacement of one component of the binary with a supermassive black hole. This scenario takes candidate of relativisti©velocity stars outside our Galaxy, into intergalactic space, where they could be ejected from merging galaxies populated by supermassive black holes. At present, this is a hypothetical class of stars with anomalous kinematics, but it is already posing a serious challenge for modern astrometry, which, like 300 years ago, is still concerned with the detection of proper motions. While this was related to stars in the solar neighborhood at the time of Halley, is now a problem for studies of the most remote and weakest stars in intergalactic space. Possibilities for detecting such stars must be based on estimates of their abundances, that is, on their statistics. This paper is based on a presentation made at the conference “Modern Astrometry 2017,” dedicated to the memory of K.V. Kuimov (Sternberg Astronomical Institute, Moscow State University, October 23–25, 2017).