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fusion
each small nucleus has a positive charge so they will repel, to make the nuclei come close enough together that the strong force attracts them, they must be thrown together at high velocities.
thus the matter must be heated up to extremely hot temperatures, almost core of sun or thrown in a particle accelerator
fusion reaction produces a lot of energy per unit mass of fuel
stellar stability
nuclear fusion causes radiation pressure to maintain equilibrium which counteracts the gravitational force from collapsing
Hertzsprung- Russell diagram
scatterplot of stars showing the relationship between star’s absolute magnitudes or luminosities and their stellar classifications or effective temperatures
what is the life cycle of a star
stellar nebula - massive star - red supergiant- supernova - neutron star or black hole
stellar nebula - average star - red giant - planetary nebula - white dwarf
how do stars start their life
in giant molecular clouds called nebulae, if gas is compressed by the shock wave from an exploding star or collision between clouds, gravity overcomes the thermal pressure, and clouds begin to collapse from different-sized stars
as they collapse they emit IR radiation.
gravity keeps collapsing the protostar until the center becomes dense and hot and hydrogen nuclei start to fuse to make helium. This releases energy, as mass of products is less, which mass is converted to energy
the outwards radiation pressure counteracts inwards gravitational pressure. Now main sequence star
nebulae
contain clouds of gas and dust left over after the formation of a galaxy, made up of mainly hydrogen.
temp about 10K, the reason why molecules present
clouds are held together by gravity but kept from collapsing from pressure of molecules moving in random motion.
protostar
a new star
fusion in core of star
hydrogen to helium
sun sized star to main sequence star
the star also shrinks but its outside stays cool until the inside gets so hot that it heats the outer layer
luminiousty of big stars to main sequence stars
stays constant as they are getting smaller but hotter
small stars to main sequence stars
the core of a small star never gets that hot, so it gets less and less bright as it contracts
main sequence
all main sequence stars have a core that is undergoing fusion from hydrogen to helium. this radiates energy, that causes a pressure that prevents the star from collapsing under the force of gravity
red giant
goes to red giant
as hydrogen fuses helium, the heavier helium sinks to the core, which is the densest and hottest part of star. Hydrogen fusion continous until pressure and temperature are no longer great enough and fusion slows. this causes the core to stop collapsing as hydrostatic equilibrium is broken. This collapse increases core temperatures, heating the outer layer of the star causing expansion
white dwarf
as the core continues to be compressed, it comes to the point where electrons cannot get closer. thus core cannot get smaller but continues to get hotter. This leads helium to fuse into berillium and then forms carbon than oxygen.
the outer layer is far from the center of core, so the force of gravity to hold them together is weka, leading for it to slowly be blown away.
the core is no longer producing energy so contract until electrons prevent it from getting smaller the
short characteristic of red giant
a cool star that gives out a lot of energy must be very big. the luminosity 100 times greater than sun. if they are same temp as sun, they must have an area 100 times greater, thus radius 10 times bigger
short characteristic of white dwarf
small hot star, hotter than the sun, but only the size of the earth. they have low luminosity
large stars
with stars of a mass over 4m, the pressure generated in core is enough to enable carbon and oxygen to fuse into larger elements such as neon and magnesium the
for stars of 8m process continuous until iron is formed
type II supernova
from an 8M star iron is fused, and fusing iron with other elements to produce larger nuclei will not liberate energy as it is on top of the binding energy curve
as the core runs out of nuclear energy, the core collapses, increasing the temperature. this allows iron to fuse, absorbing energy
this causes electrons to combine with protons to form neutrons
this continues until core-only neutrons , and there is a collapse between the core and outer layer causing explosion leaving everything but the core
neutron star or black hole
the core remained from type II supernova
black hole double size of a neutrino star (5 - 2.5)
variable star
changing luminosity , so position on HR diagram not constant. This is due to the change in size of star. As it gets bigger luminosity increases, the variation is called Cepheid variable
arcsecnond
how a star’s distance is calculated, the angle from the sun to the earth on one side,
1 arc second = 1/ parsec
