Topic 8 - Stellar Evolution

Question 1

What do stars initially form from?

Answer 1

A cloud of dust and gas called a nebula

Question 2

How is a protostar formed?

Answer 2

The force of gravity pulls the dust and gas together

Question 3

what happens as the protostar gets denser

Answer 3

temperature rises, more particles collide

Question 4

what happens when the temperature gets high enough in a protostar

Answer 4

hydrogen nuclei undergo nuclear fusion to form helium nuclei

Question 5

what does the nuclear fusion do?

Answer 5

Releases a large amount of energy keeping the core hot.

Question 6

what is the evolution of a star much bigger than the sun?

Answer 6

nebula, protostar, main sequence, red supergiant, supernova, neutron star/black hole

Question 7

what is the evolution of a star that’s about the same size as the sun?

Answer 7

nebula, protostar, main sequence, red giant, white dwarf

Question 8

what happens after the protostar phase

Answer 8

the star enters a long stable period

Question 9

what is the star called in this stable period? (after protostar)

Answer 9

a main sequence star

Question 10

Why is the star stable in the main sequence phase?

Answer 10

the outward pressure caused by thermal expansion balances the force of gravity pulling everything inwards

Question 11

how long does the main sequence period typically last

Answer 11

several billion years

Question 12

what affects how long the main sequence phase lasts and how

Answer 12

the weight of the star, the heavier the star the shorter the star is a main sequence

Question 13

what ends the main sequence period?

Answer 13

the hydrogen in the core runs out

Question 14

what does the hydrogen running out in a star’s core cause?

Answer 14

the force due to gravity becomes larger than the pressure of thermal expansion

Question 15

what does the force imbalance (larger gravitational force compared to thermal expansion) in stars cause?

Answer 15

the star is compressed until it is so dense and hot that the energy created makes the outer layers of the star expand.

Question 16

what does a main sequence star become

Answer 16

a red giant (small star) or a red supergiant (large star)

Question 17

why are red super giants and giants red?

Answer 17

the surface cools

Question 18

what happens to a red giant when it becomes a white dwarf

Answer 18

it becomes unstable and ejects its outer layer of dust and gas, leaving behind a hot, dense solid core

Question 19

what happens to a red supergiant when it becomes a supernova?

Answer 19

they undergo more fusion to make heavier elements. they expand and contract several times, and eventually explode into a supernova

Question 20

what happens as a supernova explodes?

Answer 20

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.