•Q 1: If we discover a type 1a supernova in a
distant galaxy that at its brightest has an apparent magnitude of 17, how far away is the galaxy?
(Assume the supernova has an absolute
magnitude of -19.)
–D =
10^(m-M+5)/5, so 160 Mpc
•Q 2: If a galaxy has a radial velocity
(redshift) of 5000 km/s, how far away is it? Assume a Hubble Constant of 70 km/s/Mpc.
–V =
HxD, so D=v/H, or 5000/70 Mpc = 71 Mpc
•Q 3: A quasar is observed to have a redshift
z=0.5. What recessional velocity does this correspond to?
–v/c
= ((z+1)2-1)/((z+1)2 +1) = 1.25/3.25 = 38%
•Q 4: If we take a spectrum of a quasar and see that
the Lyman alpha line, observed in the laboratory at a wavelength of 121.6 nm, appears
at a wavelength of 425.6 nm, what is the redshift of this quasar?
–Z =
Δλ/λ =
(425.6 -121.6)/121.6 = (425.6/121.6) – 1 = 3.5 – 1 = 2.5
•Q 5: Quasars can be 1000 times more luminous
than an entire galaxy. The absolute magnitude of such a luminous quasar would be about M
= -28.5. If the black hole in the center of our galaxy became a quasar, and obscuring
gas and dust did not dim it, what would the apparent magnitude of the galactic core be?
Think about the answer and what
that would look like in the sky.
–m
– M = -5 +5logd, so m = -5 +5log8.5k + M = -13.9 (about like the full
moon!)
•Q 6: If Galaxy A is four times more distant
than Galaxy B, then according to the Hubble Law, the recessional velocity of Galaxy A is
larger than that of Galaxy B by what
factor?
–V =
HxD which is a linear relationship, so V is 4 times larger.