Astronomy Exam (#3 Stellar Life Cycle)

When is a star on the main sequence?

when it is fusing hydrogen into helium in its core

the energy released by fusion produces pressure that helps support the star against the inward pull of gravity

main sequence stage characterized by

hydrogen fusion in its core

a balance between the inward force of gravity and the outward pressure within the star

a relatively stable period of a star’s life

Low mass stars hydrogen fusion

primarily done through the proton-proton chain

C-N-O cycle

a pathway for hydrogen fusion in high mass stars

What happens when a star evolves away from the main sequence?

it can expand greatly and become a giant or a supergiant

1. its radius increases substantially

2. its luminosity depends on both radius and surface temperature

3. if its temperature remains unchanged while its radius increases, its luminosity increases as the square of the radius

If the radius increases by a factor of 3 while the temperature stays the same, what happens to the luminosity?

it increases by a factor of 3²=9

Gas recycling in galaxies

stars return gas to the interstellar medium, allowing material to be recycled into later generations of stars and planetary systems

how Low-mass stars return material to interstellar medium

Expel their outer layers, producing a planetary nebula. This gas returns to the interstellar medium

how High-mass stars return material to interstellar medium

End their lives in supernova explosions. The expelled material forms a supernova remnant and returns gas to the interstellar medium