Life Cycle of Stars Flashcards
what determines the life cycle path a star goes towards
the mass of the star
where do massive stars and low mass stars end up
- massive stars end up as neutron stars or black holes
- low mass stars end up as white dwarfs
what is the simple version for the life cycle of a low mass star
- protostar
- main sequence star
- red giant
- planetary nebula
- white dwarf
what is the simple version for the life cycle of a massive star
- protostar (bigger)
- blue supergiant
- red supergiant
- type 2 supernova
- neutron star or black hole
how does a protostar become a main sequence star
- nuclear fusion of hydrogen in the core of the protostar causes it to expand and garner more mass from its surroundings
- the increase of mass increases the strength of its gravity trying to compress the star
- this happens until a delicate balance between the outward thermal expansion of fusion and inward compression of gravity is reached
how does a main sequence star become a red giant
- the star starts running low on hydrogen, but the amount of energy its produced causes it to expand
- the expansion of the outer layers causes them to cool, making them red and increasing the stars size
how does a red giant become a planetary nebula
- when most of the hydrogen is used helium will start to fuse
- this process can cause an explosion that throws the outer layers of the star into space
- this forms a planetary nebula around the star
how does a planetary nebula become a white dwarf
- the star runs out of fuel so thermal expansion decreases
- therefore gravity to take over which contracts it to a much smaller size
- this heats up the core significantly, making it a white dwarf
practically, what will happen to the white dwarf after it has reached this stage
it will gradually run out of the energy it has and eventually become cool
what is it called during this after-stage
- a red dwarf
- then eventually a black dwarf
why are black dwarfs still considered to be theoretical however
- it takes a white dwarf longer than the current age of the universe to cool this much
- so there hasnt been time for any to actually develop yet
what condition needs to be met for a protostar in order for it to go down the neutron star / black hole route
it needs to have more than 4 times the mass of our sun at that stage
what is formed from protostars this large
blue supergiants
because the core temperature of blue supergiants is significantly higher than main sequence stars, how does their fusion of hydrogen differ
- the hydrogen nuclei fuse at a much quicker rate
- so the fuel burns out very quickly in bigger stars
what further occurs due to these high temperatures however and what stage would the star be at this point
- the fusion of larger nuclei
- they could fuse up to iron
- during this process of fusing heavier elements it would be at the red supergiant stage
what happens to the balance between thermal expansion and gravity when the star has fused up to iron and why
- at iron nuclear fusion can no longer occur
- so the star stops producing energy and therefore a thermal expansion pressure
- this causes the balance between thermal expansion and gravity to dramatically shift in gravitys favor
what two factors contribute to the sudden dramatic shift in balance
- the fact that nuclear fusion stops altogether at iron
- and the large gravity formed from the very large mass
what happens due to this shift
- the star undergoes a massive collapse
- the sudden increase in density produces a huge burst of energy that almost bounces the collapse back out
- forming an explosion called a type 2 supernova
what is so incredible about supernovae
- they are the most immense bursts of energy we have ever witnessed in the universe
- giving them a brightness at about 10 billion times the luminosity of our sun
why have scientists concluded that supernovae had to have occurred in the past in order for us to have elements heavier than iron in the universe
- supernovae explosions are the only entities we know of that have so much energy
- that they can cause nuclear reactions to occur that produce elements above iron
- the natural occurrence of heavier elements means supernovae had to have been doing it from the start
what is the product that these supernovae leave behind
- a neutron star
- or a black hole
- both are the core of the star
if these two arent formed, what else could happen
the entire star may be completely shattered
what is a neutron star, other than one of the possible conclusions of the life of a large mass star
- it is a small and very dense core
- composed of densely packed neutrons
- acting as the nucleons within the nucleus of the atom
what is a black hole, other than one of the possible conclusions of the life of a large mass star
- a region of space-time
- in which the gravity is so strong that it prevents anything from escaping
- including EM radiation
do neutron stars and black holes show up in the hertzsprung-russell diagram and why
- no
- because we cant measure their temperatures of luminosity with any redeemable amount of accuracy
- a black hole literally doesnt emit EM radiation
