What is the evidence to support the existence of a black hole at ...

[geoffrey]

What is the evidence to support the existence of a black hole at the center of the Milky Way?
 
  What will be an ideal response?

Question 2

Summarize the links in the distance chain that allow us to estimate distances to the farthest reaches of the universe.
 
  What will be an ideal response?

[karmakat49]

Answer to Question 1

A large amount of activity is present. There is evidence of strong magnetic fields, X-ray sources, extremely high stellar densities, an extremely energetic accretion disk, the strongest source of radio waves in the sky, and the stars and gas speed up as you get close to the core.

Answer to Question 2

We can determine the distance to solar system objects through radar ranging. This gives us an accurate distance to the Sun so that we can use stellar parallax to measure the distances to the nearest stars. Since there is a period-luminosity relationship for Cepheids, we can measure the distances to other Cepheids by just measuring the time period between peaks of brightness. Cepheids are bright enough to be observed in galaxies other than the Milky Way. Therefore, they serve as a bridge between us and standard candles in other galaxies. Once we determine the distance to another galaxy for which we have observed a white-dwarf supernova, we then can calibrate the average luminosity of white-dwarf supernovae. White-dwarf supernovae and Cepheids get us far enough away from the Milky Way that we then can calibrate Hubble's law by determining the Hubble constant. Once we know the Hubble constant, we will be able to determine a galaxy's distance from its redshift.

[geoffrey]

Thanks for the timely response, appreciate it

[T4T]

Excellent