(Astronomy) X-Ray Binary. If an X-ray binary consists of a 20-solar-mass star and a 2.25-solar-mass neutron star orbiting each other every 28.1 days, what is their average separation? (Hints: Use the version of Kepler's third law for binary stars; make sure you express quantities in units of AU, solar masses, and years.)

Match each characteristic below of a one-solar-mass star to its appropriate phase. Answer M for Main-sequence Star, or P for Protostar. If the first is M and the rest P, enterMPPPPPP). A) energy generated by nuclear fusion B) pressure and gravity are NOT precisely balanced. C) surface radiates energy at same rate that core generates energy D) radius much larger than the Sun E) energy generated by gravitational contraction F) lasts about 10 billion years G) luminosity much greater than the Sun

(Astronomy) Neutron Star Escape Velocity. What is the escape velocity at the surface of a 2.80-solar-mass neutron star that has a typical radius for this type of star? Express your answer in units of km/s.

Which of the following most correctly explains why we have not yet observed any white dwarfs derived from M stars: Group of answer choices   Most M stars end up as neutron stars or black holes.   The lifetime of M stars is longer than the age of the universe.   Most M stars are located near the edge of the universe, beyond the visible horizon.   Most M stars are members of a binary system, and the white dwarf would be obscured by the glare of the more massive companion.   White dwarfs are too dim to be observed with currently available techniques.

12 Suppose that you measure the parallax angle for a particular star to be 0.5 arcsecond. The distance to this star is A) 2 parsecs. B C 0.5 parsec. E 5 light-years. (D) 5 parsecs. 0.5 light-year.