Question

1. How did Hubble show the nebulae are separate island universes?
2. Which types of galaxies have the large amount of star formation, spirals or ellipticals? Why is this the case?
3. What is the evidence for black holes in the centers of galaxies?
4. If H=70km/s/Mpc and a galaxy is receding at 10000 km/s, how far away is it? Show your work.
5. Why do we see only bright spirals and ellipticals in distant clusters of galaxies? Is this really all the galaxies in these clusters?

Answer 1

4) given H = 70 km/s/Mpc and v = 10000 km/s

we know V = Hd => d = V/ H => d = (10000 km/s)/70 km/s / Mpc = 142.85 Mpc

2)

Astronomers have found convincing evidence for a super massive black hole in the middle of our own Milky Way galaxy, the galaxy NGC 4258, the giant elliptical galaxy M87, and several others. Scientists verified the existence of the black holes by studying the speed of the clouds of gas orbiting those regions. In 1994, Hubble Space Telescope data measured the mass of an unseen object at the middle of M87. Based on the motion of the material whirling about the middle, the object is estimated to be about 3 billion times the mass of our Sun and appears to be concentrated into a space smaller than our solar system.

For many years, X-ray emissions from the double-star system Cygnus X-1 convinced many astronomers that the system contains a black hole. With more precise measurements available recently, the evidence for a black hole in Cygnus X-1 and about a dozen other systems is very strong.