The supermassive black hole at the Galactic centre, Sagittarius A*

PHYSICS · Multi-part · Fermi University Physics · Relativity & Gravitation · Schwarzschild spacetime and the tests of general relativity · Schwarzschild spacetime and the tests of general relativity

The Geometry of Gravity, Ch Orbits and light rays in Schwarzschild spacetime

Problem

The supermassive black hole at the Galactic centre, Sagittarius A*, has mass M=4.3×106 M⊙M = 4.3\times10^6\,M_\odot. Use GM⊙/c2=1.48GM_\odot/c^2 = 1.48 km and 11 AU =1.496×1011= 1.496\times10^{11} m. ((a)) Find the radius of the innermost stable circular orbit (ISCO) in astronomical units. ((b)) Find the radius of the photon sphere in astronomical units.

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