Binary black hole mergers
نویسندگان
چکیده
www.physicstoday.org After decades of effort, numerical relativists can now simulate the inspiral and merger of two black holes orbiting each other. That computational triumph has come none too soon—physicists are on the verge of detecting gravitational waves for the first time, and at long last they know what to look for. Black holes are strong-field objects whose properties are governed by Einstein’s theory of gravitation—general relativity. A black hole is a region of spacetime that cannot communicate with the external universe. The boundary of that region defines the surface of the black hole, called the event horizon. Isolated black holes are remarkably simple. They are described by analytic solutions to Einstein’s equations and are uniquely parameterized by just three quantities: their mass M, spin J, and charge Q. Since charged objects in space are rapidly neutralized by the surrounding plasma, one usually assumes Q = 0 for real astrophysical black holes. Stellar-mass black holes, which have masses from several to several tens of solar masses (M⊙), can form when massive stars exhaust their nuclear fuel and undergo collapse. They were first identified in binary x-ray sources in our galaxy, accreting gas from normal stellar companions. Spinning stellar-mass black holes accreting from disks of magnetized plasma may also trigger gamma-ray bursts (GRBs). During the early history of the universe, highly massive and supermassive black holes likely formed from smaller seed black holes and grew by a combination of mergers and gas accretion. The cores of nearly all nearby bulge galaxies, including our own Milky Way, harbor a supermassive black hole with a mass between 106 and 109 M⊙. Supermassive black holes are believed to be the central engines powering quasars and active galactic nuclei (AGNs), the most energetic sources of electromagnetic radiation currently known. Black holes, it seems, are making their presence felt all over the universe.
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