astrophisc Flashcards
Hubble’s law
recession speed of galaxies is proportional to their distance from earth
constellation
- a group of stars that form a pattern in the sky
- but they are not necessarily close to each other
stellar cluster
a group of stars (gas and dust) that are held together by gravity
apparent brightness
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”
two different ways in which atomic spectra can be used to deduce physical data for stars
- 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
parallax angle measured
- relative position of the star to distant background stars is received at two times 6 months apart
- half of the angular shift = parallax angle
parallax angle less than 100 pc
beyond this distance the parallax angle is too small to be measured accurately/is less than the uncertainty of the measurement
property determine wether a star ends its life as a white dwarf or as a neutron star
mass of the star’s remnant core
Chandrasekhar limit - difference between a white dwarf and neutron star
- 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
pulsar
rotating neutron star
red super giant star
red in colour
large luminosity
low temperature
large mass
large surface area
many regions of the universe that do not contain any stars why this contradicts newton’s model of the universe
- 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
big bang model is consistent
- 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
observed redshift of light from many distant galaxies is explained
the universe is expanding
lendamaxT and big bang model
relationship between those two
or how does lenda max supports big bang theory
- 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
experimental evidence that support big bang
- Hubble showed that galaxies are moving away from each other
- showing that the universe is expanding from an originated single point
distinguish between solar system and galaxy
- a galaxy is much larger in size then a solar system
- a galaxy is more luminous
- a galaxy contains many solar systems
distinguish between planet and comet
- 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
main sequence star
- absorption lines in the spectrum correspond to the h emission spectrum
- main sequence stars are rich in hydrogen
radius of a white dwarf reaches a stable value
- the star collapses until gravitational force inwards is balance by electron degeneracy pressure outwards
international collaboration has helped to refine this value
- data collection is expensive so cost can be shared
- data from around the world can be collected
main sequence star are in equilibrium under the action of forces - equilibrium is achieved
- gravitational force inwards balanced by radiation pressure outwards
star from main sequence to final stable phase
- main sequence to red giant
- the planetary nebula carries a core of mass <1.4mo
- so becomes a white dwarf
hubble’s law assumption
rate of expansion of universe has been constant
- universe expand at a constant rate
constellation / cluster
- 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
composition of star can be determined
- absorption spectrum of the star is observed
- absorption line give an indication of the elements that make up the star
main sequence to final stage
red giant -> planetary -> white dwarf
Hubble measured the recessional velocity of galaxies
measured the redshift of the galaxies
used z = v/c to find v
prevents star from collapsing further
electron degeneracy pressure
origin of EM radiation
thermal energy
red shift
observed wavelength is greater than that emitted
CMB evidence for big bang model
- 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
observation of spectra from distant galaxies provide evidence that the universe is expanding
distant galaxies have their spectra red shifted
sun become a red giant
- 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.
sun maintain a constant radius after it becomes a white dwarf
electron degeneracy pressure prevents further contraction
light spectra of distant galaxies confirm hypotheses about the expansion of the universe
- spectra are redshifted
- galaxies are moving away from us
Hubble unlikely to predict the age of the universe
assumes the universe has a constant rate of expansion
there is uncertainty in the value of Ho
asteroids
lump rock
between mars and Jupiter in the asteroid belt
