3.9.3 Cosmology. The better version (finish later)

Question 1

Define Doppler shift

Answer 1

The compressing or spreading out of waves emitted or reflected by a moving source

Question 2

What can Doppler shift be used for?

Answer 2

Studying binary stars
Evidence for the Big Bang
Identifying exoplanets

Question 3

What are the formulas for redshift?

Answer 3

z = v/c = ∆f/f = -∆λ/λ

Question 4

Describe how Doppler shift can be used to detect binary star systems

Answer 4

When both stars are at 90 degrees to our line of sight, they produce one line on the absorption spectrum.
When they are both along our line of sight, there are 2 lines - one has maximum blueshift because it is moving towards us, the other has maximum redshift because it is moving away from us.
0 separation to maximum separation is half the time period of orbit.

Question 5

What are the difficulties in detecting binary star systems

Answer 5

They are too far away to be resolved with telescopes

Question 6

What are the properties of quasars?

Answer 6

They are active radio sources
Massive redshift
… hence very far away
Powerful galactic nuclei containing an active black hole surrounded by a disc of whirling gas and is actively taking in matter. They are formed AROUND the black hole.

Question 7

Why are exoplanets hard to detect?

Answer 7

• They orbit stars brighter than themselves, brightness of the star drowns out the brightness of the exoplanet.
• They are too small to distinguish from nearby stars which are brighter than them (the subtended angle is too small for the resolving power of telescopes

Question 8

What detection methods are used to detect exoplanets?

Answer 8

Direct observation
Radial velocity
Transit method