MODULE 8 IQ 1

Question 1

cosmological principle

Answer 1

universe is isotopic and homogeneous

Question 2

Alexander Friedmann

Answer 2

used Einstein’s theory of general relativity to provide evidence for the universe to be expanding

Question 3

edwin hubble discoveries

Answer 3

the further the galaxies were moving away from the Earth, the greater the degree of the red shift –> translational velocities are greater
- first evidence of the expanding universe

Question 4

edwin hubble equation

Answer 4

v = H(0)d

Question 5

big bang model

Answer 5

universe originated from a singularity
- as the universe expands, the energy density and thus temperature drops
- when temperatures are cooler, complex particles are able to be formed

Question 6

timeline of big bang

Answer 6

big bang, inflationary epoch, quarks/leptons era, nucleons, nucleosynthesis, photon epoch, dark ages, accretion

Question 7

the big bang time of big bang timeline

Answer 7

temperature : 10^32 K
time: <10^-43 s
- beginning of the Grand unified Theory (GUT)
- gravity separates from the fundamental forces

Question 8

inflationary epoch during big bang timeline

Answer 8

universes expanded at a factor of 10^26 in all directions
time: <10^-32 s
- strong force separates from the electroweak force
- rapid expansion explains the cosmic microwave background radiation (CMBR, 2nd evidence for why the universe is expanding) which is almost uniform

Question 9

quarks/leptons era during big bang timeline

Answer 9

• universe has cooled enough for matter to form
  time: <10^-6 s
• electromagnetic and weak force separate

Question 10

4 fundamental forces

Answer 10

gravity
electromagnetic force
electroweak force
strong force

Question 11

nucleons in the big bang timeline

Answer 11

• quarks combine to form protons:neutrons (7:1)
  time: <10^-4 s

Question 12

nucleosynthesis in big bang timeline

Answer 12

p + n –> nuclei
time: 225-1000 years
- 1/4 of universe mass is helium nuclei while rest if hydrogen nuclei –> initially, the universe was radiation dominant
- universe is opaque

Question 13

photon epoch + recombination in big bang timeline

Answer 13

• photon decoupling photons (fall out of thermal equilibrium with each other) –> universe becomes transparent
• incited CMBR (microwave radiation –> long wavelength & shortest frequency)

Question 14

dark ages in the big bang timeline

Answer 14

• no visible or infrared light as there were no stars
  time: 377 000-400 million years

Question 15

accretion in the big bang timeline

Answer 15

• increase of matter –> gravity –> organisation into large scale structures such as stars and galaxies
• protostars begin to form
• temperature cooled down by a factor that allowed particles to be affected by gravity
• increase in gravity –> clouds of hydrogen and helium –> fusion –> heat and light

Question 16

what is big bang nucleosynthesis

Answer 16

main sequence stars fuse hydrogen into helium

Question 17

what are the type of big bang nucleosynthesis

Answer 17

proton-proton chain, CNO cycle, triple-alpha process

Question 18

what type of stars does proton-proton chain occur in

Answer 18

smaller, cooler stars

Question 19

proton-proton chain overall equation

Answer 19

4^1H → ^4He + 2e^+ + 2v + 2(gamma)

Question 20

what type of stars does CNO cycle occur in

Answer 20

bigger MS stars
- faster fusion sequence

Question 21

CNO cycle overall equation

Answer 21

4^1H → ^4He + 2e^+ + 2v + 3(gamma)

Question 22

when does triple alpha process occur

Answer 22

when MS star burns up into red giant

Question 23

triple alpha process equations

Answer 23

^4He + ^4He → ^8Be + ^4He
^8Be + ^4He → ^12C + ^4He
^12C + ^4He → ^16O (most stable oxygen)

Question 24

luminosity in Hertzsprung-Russell Diagram

Answer 24

total power radiated given by
L = 4(pi)d^2b

Question 25

apparent brightness in H-R diagram

Answer 25

power received by a star from an observer at a point of reference per unit area b = L/4(pi)d^2

Question 26

spectral class H-R diagram

Answer 26

OBAFGKM - divided from 0-9 - temperature and spectral class are related to star's colour

Question 27

magnitude in H-R diagram

Answer 27

more positive absolute magnitude are SMALLER

Question 28

main sequence stars

Answer 28

- 90% of all stars - produce energy by fusing hydrogen into helium

Question 29

red giants

Answer 29

- above MS stars, underneath supergiants - evolve from smaller MS stars after they have depleted their hydrogen source

Question 30

supergiants

Answer 30

- top of HR diagram - extremely luminous due to large SA - lower intensity of radiation --> low surface temperatures

Question 31

white dwarfs

Answer 31

- bottom left of HR diagram - remnants of old stars with high surface temperature but no energy production left - low luminosity due to small SA

Question 32

brown dwarfs

Answer 32

- bottom right of HR diagram - fuses hydrogen into helium slowly, lasts forever

Question 33

evolutionary path of small MS star

Answer 33

hydrogen fusing into helium --> when all hydrogen is fused --> gravitational collapse --> higher temperature --> helium fuses to larger elements --> increased outwards radiation pressure --> red giant

Question 34

evolutionary path of red giant

Answer 34

fusion in core with larger elements --> star shrinks --> outer layers are blown away due to electrostatic separation --> gaseous planetary nebula --> white dwarf

Question 35

evolutionary path of large MS star

Answer 35

large MS star --> red supergiant --> huge repulsion between nuclei --> supernova --> blows away most of star mass --> neutron star or black hole