x-ray pulses from cygnus x-1, a celestial xray source, have been recorded during highaltitude rocket flights. the signals can be interpreted as originating when a blob of ionized matter orbits a black hole with a period of 6.62 ms. if the blob were in a circular orbit about a black hole whose mass is 19.1 times the mass of the sun, what is the orbit radius? the value of the gravitational constant is 6.67259 × 10−11 n · m2 /kg2 and mass of the sun is 1.991 × 1030 kg. answer in units of km