Cosmology

Question 1

What is the class order, colour and surface temperature in K (approx.)?

Answer 1

• Oh, Blue, >33000
• Be, Blue
• A, White, 9000
• Fine, Yellow
• Girl, Yellow, 6000
• Kiss, Orange
• Me, Red, 3000

Question 2

What is a star’s colour related to?

Answer 2

Its surface temperature

Question 3

Why is a star’s colour related to its surface temperature?

Answer 3

Wien’s Displacement law: λT = 2.910^-3

Question 4

What is the evolution of a star with similar mass to the sun?

Answer 4

1. Protostar
2. Main sequence star
3. Red giant
4. Planetary nebula
5. White dwarf

Question 5

What is the evolution of a star more massive than the sun?

Answer 5

1. Protostar
2. Main sequence star
3. Red supergiant
4. Super Nova
5. Black hole (most massive) or neutron star

Question 6

What is a protostar?

Answer 6

A region of dust or gas where the mass is influence by a gravitational force which causes all of it to accelerate towards the centre. The GPE is converted to KE which increases the temperature in the core. If temperature and pressure are higher enough then H fusion can occur

Question 7

What is a main sequence star?

Answer 7

H -> He fusion releases energy which causes the star to heat up causing it to expand. Hydrostatic equilibrium is when the outside pressure from temperature equals the inwards pressure from gravity

Question 8

What is a red giant?

Answer 8

Once the star runs out of H the star stars collapsing. This causes the core to heat up allowing higher elements to fuse (which depends upon original mass). The star starts to die

Question 9

What is absolute brightness or magnitude?

Answer 9

A measure of how bright a star would be at standard distance (10 parsecs) allowing for more accurate comparison between stars

Question 10

(λ-λ_o)/λ_o

Answer 10

v/c

Question 11

What does red light have?

Answer 11

A longer wavelength

Question 12

What does blue light have?

Answer 12

A shorter wavelength

Question 13

How do we measure redshifts?

Answer 13

Using the spectrum of light from a star or galaxy which is crossed by dark vertical lines which correspond to wavelengths of light which are absorbed by cooler gases in the outer layers of stars

Question 14

How does redshift provide evidence for the expansion of the universe?

Answer 14

• Light from stars and galaxies moving away from us is redshifted - the wavelength of emitted light is longer
• Light from stars and galaxies moving toward us is blueshifted - the wavelength of emitted light is shorter
• The further away a galaxy is the faster it is receding and the greater the redshift
• All distant galaxies are moving away from each other
• There is no centre to the universe

Question 15

What is recession velocity?

Answer 15

How quickly something is moving away due to expansion

Question 16

What is a light year?

Answer 16

The distance light travels in a year

Question 17

What does Cosmic Microwave Background Radiation (CMBR) tell us?

Answer 17

• After the big bang the radiation emitted will have cooled as it spread out in the universe and since it is expanding it will continue to cool
• T_universe=2.3K λT = 2.910^-3
• This is equivalent to energy that is expected in microwaves
• A radiotelescope can detect a constant hum of microwaves in the sky