Cosmology

Question 1

State the cosmological principle

Answer 1

The universe is isotropic and homogenous and the laws of physics are universal

Question 2

State the definition of isotropic in relation to the universe

Answer 2

It appears the same in all directions

Question 3

State the definition of homogenous in relation to the universe

Answer 3

It has a constant matter density

Question 4

State Hubble’s Law

Answer 4

The recession speed of a distant galaxy is directly proportional to its distance from the Earth - v = Hd

Question 5

State the evidence for the expansion of the universe

Answer 5

• Huge redshift - galaxies are moving away from us
• CMB waves match theoretical spectrum of thermal radiation from an object at 2.7K
• directed in all directions and intensity did not change therefore cosmic in origin
• Abundance of hydrogen and helium 3:1 ratio

Question 6

Define dark energy

Answer 6

The energy of empty spaces which seems to fuel the expansion of the universe

Question 7

Describe the stages of the Big Bang

Answer 7

• Time and space are created
• The universe rapidly expands in a period of inflation
• The first fundamental particles gain mass
• Quarks bind to form hadrons (protons and neutrons)
• As the universe is expanding it is cooling
• The universe cools enough for atoms to form
• Nuclei capture electrons
• EM radiation from this is detected as CMB radiation

Question 8

What are cosmic background microwaves?

Answer 8

Radiation released as gamma rays that has now been stretched to microwaves

• it is one of the main observational pieces of evidence for the Big Bang
• accounts for the temperature of 2.7K

Question 9

State the temperature of the universe

Answer 9

2.7K

Question 10

Define the Doppler effect

Answer 10

The compression or spreading out of waves that are emitted or reflected by a source

Question 11

State the condition for the Doppler effect

Answer 11

v«c

Question 12

State the property of quasars that led to their discovery

Answer 12

strong radio wave emitters

Question 13

Why would a quasar stop emitting radiation?

Answer 13

• They are formed around supermassive black holes
• It stops emitting radiation because the black home no longer has matter falling into it (inactive)

Question 14

What are quasars?

Answer 14

The oldest most distant measurable objects in the universe formed from supermassive black holes

They are about the size of a solar system but more luminous than a star

Question 15

State the evidence for quasars being the oldest and most distant objects

Answer 15

extremely large red shifts

Question 16

Compare GRB to quasars

Answer 16

• short lived burst (0.01-1s)
• more energetic
• has two plumes of light a the poles
• due to the collapse of a supergiant star to form black holes