Summary: ASTR 3730: Astrophysics 1 Problem Set #1
Due in class Friday 12th
1) (a) Neutral hydrogen emits radio waves with a wavelength of 21cm. What is the
frequency of this radiation?
(b) What is the wavelength (in nm) of an X-ray photon with an energy of 6.4 keV?
2) (a) A binary star system in the star forming region of Taurus (at a distance of 150
pc) has a separation between the two stars of 50 au. Can we resolve the binary (i.e.
detect the two stars individually) using a ground-based telescope with a resolution of
(b) Improved observations show that what was previously thought to be a single 16th
magnitude star is actually a close binary consisting of two identical stars. What is the
magnitude of each individual star?
3) An Active Galaxy (i.e. a supermassive black hole accreting gas from a surrounding
galaxy) at a distance of 1 Gpc produces a luminosity in X-rays of LX = 1041
(a) What is the X-ray flux at Earth from this source?
(b) The Chandra X-ray observatory observed the source for 106
s (one of the longest