Why is Einstein's general theory of relativity a better description of gravity than Newton's universal law of gravitation? Under what circumstances is Newton's description of gravity adequate?
What is a gamma-ray burster? What is the evidence that gamma-ray bursters are not located in the disk of our Galaxy or in a halo surrounding our Galaxy?
Why is it unlikely that a black hole has an electric charge?
The orbital period of the binary system containing A0620-00 is 0.32 day, and Doppler shift measurements reveal that the radial velocity of the X-ray source peaks at 457 km/s.
(a) Assuming that the orbit of the X-ray source is a circle, find the radius of its orbit in kilometers.
(b) By using Newton's form of Kepler's third law, prove that the mass of the X-ray source must be at least 3.1 times the mass of the Sun. :
What must happen within a hydrogen atom for it to emit a photon of wavelength 21 cm?
What is the winding dilemma? What does it tell us about the nature of spiral arms?
Do density waves form a stationary pattern in a galaxy? If not, do they move more rapidly, less rapidly, or at the same speed as stars in the disk?