astro physics and cosmology Flashcards
planet
objects with mass sufficient for their own gravity to force them to take a spherical shape, no nuclear fusion occurs, cleared orbit of other objects
dwarf planets
planet where the orbit has not been cleared of other objects
planetary satellite
Bodie that orbits a planet
asteroid
objects which are too small and uneven to be planets, near circular orbit around the sun
comets
small, irregularly sized balls of rock, dust and ice. they orbit the sun in an elliptical orbit
solar system
systems containing stars and orbiting objects like planets
galaxy
collection of stars, dust and gas
nebulae
gigantic clouds of dust and gas
protostar formation
- nebulae with dense regions of dust and gas
- gas pulls dust and gas together causing it to collapse
- as cloud collapses, its starts to spin and forms a rotating disk (angular momentum causes the spin)
- centre of disk, a dense core forms
- gpe is converted to thermal which heats up centre
- sphere of very hot, dense, dust and gas which os called a protostar
how are main sequence stars formed from protostars
- when protostar formed from a cloud of gas and dust, gravity pulls the material inward
- as material gets closer togther it becomes denser and hotter
- the increase in denisty and temperature leads to an increase in pressure
- pressure comes from gas particles colliding and pushing outwards
- the temp and pressure must then be high enough for hydrogen to overcome elcatrostatic forces of repulsion and undergo nuclear fusion where hydrogen is fused to helium
- fusion will occur when the pressure outward pressure balances the inward force of gravity
how does a low mass main sequence star become a red giant
- core mass of 0.5 solar masses
- smaller cooler core they remain in main sequence longer
- hydrogen supplies low g forces inwards overcome radiation and gas pressures
- core collapses and outer layers expand and cool
- core of red giant becomes hotter as gpe becomes thermal energy and it fuses helium into heavier elements up to carbon as hydrogen continues to be fused in the layers around the core
red giant to white dwarf
- star runs out of fuel it expels its outer layers resting planetary nebulae
- core contracts further becoming dense white dwarf
- no fusion occurs
- photon which were produced earlier leak out dissipating heat
- star core collapses electron degeneracy pressure prevents the. core form collapsing, as long as core mass is below 1.44 then the white dwarf is stable this is the Chandrasekhar limit
high mass main sequence into red supergiant
- mass exceeds 10 solar masses
- hydrogen supplies deplete
- core contracts
- as mass is greater when gpe is converted to thermal energy the core gets hotter than red giant allowing helium fusion into heavier elements than carbon up to iron
- outer layers expand and cool forming red supergiant
death of high mass star
- fuel in red supergiant used up fusion stops
- gravity becomes greater than outward pressure due to fusion
- core collapses in on itself and becomes rigid
- outer layers fall inwards and rebound off the core launching them into space as a shockwave
- remaining core of a supernova is either a neutron star or black hole depending on mass
red supergiant into neutron star or black hole
- core greater than 1.44 gravity forces protons and electrons to combine and form neutrons this produces small dense neutron star
- core greater than 3 the gravitational forces are so strong that the escape velocity of the core becomes greater than the speed of light this is a black hole
hertzprung - russel diagram
- top supergiants
- middle right giants
- negative linear line main sequence
- bottom left white dwarf
Chandrasekhar limit
the maximum mass that a white dwarf can have whilst remaining stable
x and y axis of hertzprung russel diagram
y axis is luminosity
x axis is temperature (increases to the left)
rules for energy levels
- electron cannot have an energy level between states
- negative as external energy os requires for an electron to escape
- lowest most negative energy level is the ground state
emission line spectra
- series of colour lines on a black background
- light passes through outer layers of a star, electrons in atom absorb photons and become excited
- they then de excite releasing photons of specific wavelengths
- these are detected on earth and have wavelengths characteristic of the elements in the outer layers, shown as emission line spectra
continues line spectra
all visible wavelengths of light are present, they are produced by atoms of solid heated metals
absorption line spectra
- dark spectral lines on coloured background
- each line corresponds to wavelength of light absorbed by atoms in outer layers of a star
- dark lines are at wavelengths that are characteristic of the elements in the outer layers
what happens when an electron is de-excited
releases energy as a photon with specific wavelength
- energy released is the difference between the initial and final energy level of photon
diffraction gratings
components with regularly spaced slits that can diffract light. different colours of light have different wavelengths and so will be diffracted at different angles
weins displacement law
wavelength of emitted radiation at peak intensity is inversely proportional to the temperature of the black body
stefans law
power output of a star is directly proportional to its surface area and to its (absolute temperature)^4
light year
distance travelled by light in vacuum in one year
doppler effect
change in wavelength and frequency of a wave as the source moves away from or towards the observer
stellar parallax
apparent shift imposition of object against backdrop of distant objects due to the orbit of the earth
parsec
the distance from which 1 AU subtends an angle of 1 arc second (1/3600 of a degree)
cosmological principle
universe is isotropic and homogenous and the laws of physics are universal
isotropic
universe is the same in all directions to envy observer and it has no centre or edge
homogenous
matter is uniformly distributed for a large volume of the universe the density is the same
red shift
shut in wavelength and frequency of waves from a retreating source towards/beyond the red end of the spectrum it is evidence of the Big Bang
Hubbles law
velocity of receding objects is directly proportional to their distance from earth
big bang theory
universe exploded from a extremely hot dense point and is still expanding
cosmic background microwave radiation is the heat signature left behind from the Big Bang
em radiation released in the explosion shifted from extremely high energy waves into the microwave region as the universe expanded stretching out the waves
dark energy
- energy that has an overall repulsive effect through out the universe
big bang times
- time and space created
- universe expand and cools in period of inflation
- fundamental particles gain mass, quarks and leptons
- quarks bind to form hadrons (protons and neutrons)
- expanding and cooling
- cools enough for atoms to form
cosmic background microwave radiation
- main observation of big bang
- radiation was released as gamma rays but now stretched to microwaves
- accounts fro temp of 2.7K
