chapter 19 - stars

Question 1

planet

Answer 1

• object in orbit around a star
• has mass large enough for own grav to give a round shape
• no fusion
• cleared its orbit of most other objects

Question 2

dwarf planet

Answer 2

• not cleared its orbit of most other objects

Question 3

asteroids

Answer 3

• too small/ uneven to be planets
• near circular orbit round sun
• no ice

Question 4

planetary satelites

Answer 4

• body in orbit around a planet
  eg moons + man made

Question 5

comets

Answer 5

• range in size
• small irregular bodies made of ice dust and small pieces of rock
• orbits sun in highly eccentric elliptical orbits
• when close to sun ice melts making tail

Question 6

galaxy

Answer 6

• collection of stars and interstellar dust /gas
• contains about 100 bill stars
  eg Milky Way

Question 7

lifecycle of a low mass star

Answer 7

nebula
protostar
main sequence
red giant
white dwarf

Question 8

lifecycle of high mass star

Answer 8

nebula
protostar
main sequence
red super giant
supernove
blackhole OR neutron star

Question 9

nebula

Answer 9

• electrostatic forces cause attraction of dust and gas (bc particles have charge)
• as mass ^ grav force ^
• dense - block light from stars - appear dark

Question 10

protostar

Answer 10

• mass ^ so g ^ and density ^ in the centre
• gravitational collapse occurs - more massive = faster collapse
• uneven distribution of mass
• GPE > thermal energy so temp increases
• hot dense core forms

Question 11

nuclear fusion

Answer 11

eg H -> He
- releases KE
- need high enough temp to bring close and overcome electrostatic repulsion

Question 12

main sequence

Answer 12

• stable equilibrium
• fusion in core causes radiation pressure outwards
• grav forces act inwards = radiation pressure
• length of stability depends on size and mass - high mass means density is larger so is hotter so time in main sequence decreases

Question 13

low mass star size

Answer 13

1/2 -10 M⊙

Question 14

red giant

Answer 14

• run out of H - reduction in fusion - grav collapse due to force imbalance
• fusion restarts in shell ( as g^ density^ increasing temp so fusion of He begins)
• inert core
  shells expand away as thermal pressure > g
• planetary nebula formed

Question 15

white dwarf

Answer 15

• inert hot dense core
• emits energy as leaks photons, no fusion occurs
• electron degeneracy stops g causing collapse
• radiates heat away - eventually forming black dwarf

Question 16

Chandrasekhar limit

Answer 16

1.4 M⊙
max mass of a stable white dwarf
if core is less becomes a white dwarf

Question 17

pauli exclusion principle

Answer 17

• all electrons are identical
• cant exist in the same quantum state
• therefore mass has structure
• can only have 2 electrons in the same energy state so the rest are forces higher - causes electron degeneracy

Question 18

large mass star size

Answer 18

> 10 M⊙

Question 19

red super giant

Answer 19

• H runs low - star collapses under own g
• core is very hot - fusion of heavier elements occurs
• series of shells form - most dense at core
• when iron core forms fusion no longer occurs (iron is stable)
• star becomes unstable

Question 20

supernova

Answer 20

• once a stars core is converted to iron no further fusion - star collapse rapidly - resulting in supernova
• absolute magnitude increases massively
• core is left and compressed into a blackhole or neutron star
• elements heavier than iron are formed in the supernova

Question 21

black hole >3M⊙

Answer 21

• grav collapse of core to an infinitely dense point (singularity)
• escape v > speed of light
• super massive backholes are thought to be centre of most galaxies
• event horizon - boundary at which escape v = speed of light - nothing can escape within it

Question 22

neutron star 2-3M⊙

Answer 22

if mass of core > Chandrasekhar limit core continues to collapse forming a neutron star
- electron degeneracy cant counter grav force
- electrons are squeezed into protons of the atoms - making neutrons
- consist of mostly neutrons - small and dense
- rotate fast and some emit radio waves - observed as radio pulses

Question 23

Schwarzschild radius

Answer 23

• radius of an imaginary sphere such that if the mass of an object is compressed into this sphere its escape v> c
• radius of black hole must be smaller than rs
  rs = 2GM/c^2
  KE lost = GPE gain
  1/2mv^2 = GMm/r

Question 24

energy levels

Answer 24

electrons are bound to their atoms - can only exist in certain energy levels - cant be between
- are negative - energy required to remove from atoms
- 0 energy means free
- most negative level is ground state

Question 25

excited

Answer 25

electron moves from ground state to higher level eg by heating, an electric field, absorbing photons of specific λ, collisions with incoming electron

Question 26

de excites

Answer 26

gives off a photon of a specific λ atoms with specific energy levels give off photons with specific λ - identified by light - E = hf = E2 -E1 difference in energy levels

Question 27

spectra

Answer 27

evidence for energy levels if you view through diffraction grating splits into colours

Question 28

emission spectra

Answer 28

cool gas heated excited gas emits photons electrons return to ground state and give out specific λ photons - represent energy levels of that gas - dark with coloured lines

Question 29

continuous spectra

Answer 29

- when you heat a solid metal atoms eg filament lamp - see all visible λs - look like white light

Question 30

absorption spectra

Answer 30

white light passed through cool gas - λ absorbed - as photons pass through a cold gas electrons absorb freqs causing electrons to be excited up an energy level - these freqs / λs are mssing from the continuous spectra - specific to an element as electrons occupt discrete energy levels (coloured spectra with specific black liens)

Question 31

black bodies

Answer 31

- emit all λ of light eg sun, hot metal - distribution of λ depends only on temp - peak shifts left as temp increases (E prop to 1/λ) E = nhf