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physic > astrophisc > Flashcards

astrophisc Flashcards

1
Q

Hubble’s law

A

recession speed of galaxies is proportional to their distance from earth

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2
Q

constellation

A
  • a group of stars that form a pattern in the sky
  • but they are not necessarily close to each other
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3
Q

stellar cluster

A

a group of stars (gas and dust) that are held together by gravity

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4
Q

apparent brightness

A

the power per square metre received by an observer on earth

is the amount of ENERGY received per second per unit area by an observer”

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5
Q

two different ways in which atomic spectra can be used to deduce physical data for stars

A
  • absorption spectra give information on the element that make up the star
  • the peak of wavelength gives information on the temperature of the star
    doppler shift gives information on the stars motion relative to earth
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6
Q

parallax angle measured

A
  • relative position of the star to distant background stars is received at two times 6 months apart
  • half of the angular shift = parallax angle
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7
Q

parallax angle less than 100 pc

A

beyond this distance the parallax angle is too small to be measured accurately/is less than the uncertainty of the measurement

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8
Q

property determine wether a star ends its life as a white dwarf or as a neutron star

A

mass of the star’s remnant core

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9
Q

Chandrasekhar limit - difference between a white dwarf and neutron star

A
  • defines the maximum mass of a white dwarf
  • up to this limit electron degeneracy pressure prevents further gravitational collapse
  • above this, gravity overcomes this forming a neutron star
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10
Q

pulsar

A

rotating neutron star

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11
Q

red super giant star

A

red in colour
large luminosity
low temperature
large mass
large surface area

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12
Q

many regions of the universe that do not contain any stars why this contradicts newton’s model of the universe

A
  • newton’s model states that universe is infinite and uniform
  • so there must be a star along every line of light from earth making the sky bright at night
  • but as there are regions without stars newton’s model is incorrect
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13
Q

big bang model is consistent

A
  • space and time originated with the big bang
  • universe is expanding
  • due to expansion light from distant stars has not yet reached / or has been redshifted to infrared and is not visible
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14
Q

observed redshift of light from many distant galaxies is explained

A

the universe is expanding

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15
Q

lendamaxT and big bang model

relationship between those two
or how does lenda max supports big bang theory

A
  • the neutral temperature of the universe was very high after the big bang
  • due to expansion and time, the temperature has now fallen to 2.7k
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16
Q

experimental evidence that support big bang

A
  • Hubble showed that galaxies are moving away from each other
  • showing that the universe is expanding from an originated single point
17
Q

distinguish between solar system and galaxy

A
  • a galaxy is much larger in size then a solar system
  • a galaxy is more luminous
  • a galaxy contains many solar systems
18
Q

distinguish between planet and comet

A
  • a comet is a small icy body whereas a planet is made of rock and gas
  • comets have larger orbits then planets
  • comets often have tails, planets do not
19
Q

main sequence star

A
  • absorption lines in the spectrum correspond to the h emission spectrum
  • main sequence stars are rich in hydrogen
20
Q

radius of a white dwarf reaches a stable value

A
  • the star collapses until gravitational force inwards is balance by electron degeneracy pressure outwards
21
Q

international collaboration has helped to refine this value

A
  • data collection is expensive so cost can be shared
  • data from around the world can be collected
22
Q

main sequence star are in equilibrium under the action of forces - equilibrium is achieved

A
  • gravitational force inwards balanced by radiation pressure outwards
23
Q

star from main sequence to final stable phase

A
  • main sequence to red giant
  • the planetary nebula carries a core of mass <1.4mo
  • so becomes a white dwarf
24
Q

hubble’s law assumption

A

rate of expansion of universe has been constant
- universe expand at a constant rate

25
Q

constellation / cluster

A
  • stars in a cluster are close together, these in a constellation are not
  • stars in a cluster are held together by gravity, those in a constellation are not
  • stars in a cluster are the same age these in a constellation are not
26
Q

composition of star can be determined

A
  • absorption spectrum of the star is observed
  • absorption line give an indication of the elements that make up the star
27
Q

main sequence to final stage

A

red giant -> planetary -> white dwarf

28
Q

Hubble measured the recessional velocity of galaxies

A

measured the redshift of the galaxies
used z = v/c to find v

29
Q

prevents star from collapsing further

A

electron degeneracy pressure

30
Q

origin of EM radiation

A

thermal energy

31
Q

red shift

A

observed wavelength is greater than that emitted

32
Q

CMB evidence for big bang model

A
  • the CMB comes from all regions of space it is uniform
  • the wavelength of the CMB matches that predicted by coding of the universe after the big bang / or by expansion of the universe
  • coding the wavelength of CMB matches the prediction that universe is expanding
33
Q

observation of spectra from distant galaxies provide evidence that the universe is expanding

A

distant galaxies have their spectra red shifted

34
Q

sun become a red giant

A
  • fusion of hydrogen in the core stops and the core contract helium fusion now begins in the core causing the sun to expand and become more luminous.
35
Q

sun maintain a constant radius after it becomes a white dwarf

A

electron degeneracy pressure prevents further contraction

36
Q

light spectra of distant galaxies confirm hypotheses about the expansion of the universe

A
  • spectra are redshifted
  • galaxies are moving away from us
37
Q

Hubble unlikely to predict the age of the universe

A

assumes the universe has a constant rate of expansion
there is uncertainty in the value of Ho

38
Q

asteroids

A

lump rock
between mars and Jupiter in the asteroid belt

physic (5 decks)

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