Question

1. What is the evidence for a black hole at the center of the Milky Way? How does this compare to stellar size blackholes? How can these smaller blackholes be observed?

2. What is Hubble’s Law? In what situations does Hubble’s Law not apply?

3. What is the cosmic microwave background? What is its origin?

Answer 1

Because whole Milky Way rotates around the Centre, also near the centre there is very hot gas cloud rotating very fast which suggest the presence of a supermassive black hole at the centre of Milky Way.
stellar blackhole and 10 to 100 times mass of sun whereas the black hole at the very centre of Milky Way is nearly 4,300,000 times solar Mass.

Stellar blackhole are typically formed by collapse of a massive stars which in process cause hypernova explosion hence Gama Ray Burst that's the main way to observe them.

according to hobbles law further the Galaxy is faster it moves away from us. Hubble's law is not applicable to star cluster because in a large star cluster the star rotates around the cluster which cause them to have an additional velocity and that's create problem in applying the law.

cosmic microwave background radiation is the leftover of radiation from big bang itself. Its origin was the phenomena of big bang