Astrophysics midterm 2 conceptual questions

What is the Lyman-alpha forest?

Emission and absorption lines of hydrogen. It tells you the fluctuations in density of the hydrogen along a line of sight to a quasar.

What does the ratio of deuterium to hydrogen in the early universe tell us?

It gives the baryon to photon ration of the universe. Which provides insight to the conditions during Big Bang nucleosynthesis.

At what time after the big bang did helium form?

Within the first few minutes, nucleosynthesis.

Where are the heavy elements produced?

Within the cores of massive stars.

What is the temperature of the CMB today?

2.725 Kelvin

What are the two physical principles our pressureless dust cosmology is based on?

The copernican principle and the cosmological principle

How does a quasar produce its energy?

Massive black holes in the center of galaxies. Forming accretion disks and then getting converted into EM radiation.

What is Olber's paradox?

the argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe

What is the effect of dark energy on the universe?

It accelerates the expansion of the universe.

In the equation, what does (8/3)piGro represent?

Potential energy of the expanding shell.