Topic 8 - Stellar Evolution Flashcards
What do stars initially form from?
A cloud of dust and gas called a nebula
How is a protostar formed?
The force of gravity pulls the dust and gas together
what happens as the protostar gets denser
temperature rises, more particles collide
what happens when the temperature gets high enough in a protostar
hydrogen nuclei undergo nuclear fusion to form helium nuclei
what does the nuclear fusion do?
Releases a large amount of energy keeping the core hot.
what is the evolution of a star much bigger than the sun?
nebula, protostar, main sequence, red supergiant, supernova, neutron star/black hole
what is the evolution of a star that’s about the same size as the sun?
nebula, protostar, main sequence, red giant, white dwarf
what happens after the protostar phase
the star enters a long stable period
what is the star called in this stable period? (after protostar)
a main sequence star
Why is the star stable in the main sequence phase?
the outward pressure caused by thermal expansion balances the force of gravity pulling everything inwards
how long does the main sequence period typically last
several billion years
what affects how long the main sequence phase lasts and how
the weight of the star, the heavier the star the shorter the star is a main sequence
what ends the main sequence period?
the hydrogen in the core runs out
what does the hydrogen running out in a star’s core cause?
the force due to gravity becomes larger than the pressure of thermal expansion
what does the force imbalance (larger gravitational force compared to thermal expansion) in stars cause?
the star is compressed until it is so dense and hot that the energy created makes the outer layers of the star expand.
what does a main sequence star become
a red giant (small star) or a red supergiant (large star)
why are red super giants and giants red?
the surface cools
what happens to a red giant when it becomes a white dwarf
it becomes unstable and ejects its outer layer of dust and gas, leaving behind a hot, dense solid core
what happens to a red supergiant when it becomes a supernova?
they undergo more fusion to make heavier elements. they expand and contract several times, and eventually explode into a supernova
what happens as a supernova explodes?
the outer layers of dust and gas are thrown into space, leaving a very dense core (a neutron star). if the star is big enough it will collapse and become a black hole.
