The direct observation of gravitational waves with new generation instruments (LIGO, Virgo, LISA) opens new opportunities for the study of neutron stars, black holes, and other relativistic binary stars.
Black Holes Physics:
Black holes deform the space-time around them. They are possibly the most fascinating objects in the Universe. Black holes are highly dense spherical conglomerates of rotating matter, exhibiting strong gravitational effects. In 2015 LIGO team succeeded at detecting gravitational waves from colliding black holes.
Structure and Evolution of Binary Systems:
A binary star system is a gravitationally bound two components that orbit around their center of mass. Most stars in the sky are in binary or even triples and quadruplets. They are very important objects in Astronomy and Astrophysics. Photometric and spectroscopic observations of binary and multiple systems allow one to determine accurate physical and orbital parameters of component stars. We can test stellar formation, structure, and evolution using binary parameters.