Astronomy Flashcards
1
Q
What happens within the main sequence phase of a star’s life?
A
- radiation pressure due to fusion is same as inward gravitational force of star
- star is in equilibrium
2
Q
What happens when hydrogen runs out in low mass stars?
A
- rate of fusion drops
- results in inward collapse of star
- GPE —> KE, results in temperature rise
- fusion in shells around core occurs
- shells expand, cool, emit low wavelength EM waves (red)
3
Q
What happens as hydrogen in shells runs out in a low mass star?
A
- rate of fusion drops off, star cools
- mass of shells is lost to space
- star collapses, only hot core left
- white dwarf
4
Q
What are the characteristics of the white dwarf?
A
- very dense
- mass similar to sun
- volume similar to earth
- no fusion occurs within white dwarf
- leaks photons created earlier on in life
- very hot
5
Q
What opposes the gravitational force in white dwarfs?
A
- electron degeneracy pressure
6
Q
What is the electron degeneracy pressure?
A
- Pauli exclusion principle dictates that 2 electrons cannot occupy the same energy state
- means that electrons resist being pushed close to each other (electron degeneracy pressure)
7
Q
What is the value of the Chandrasekhar limit?
A
- 1.44 solar masses
8
Q
What is the significance of the Chandrasekhar limit?
A
- cores that are are heavier than this value will continue to collapse past the white dwarf stage
- as electron degeneracy pressure is not enough to counter gravitational force
- become black holes or neutron stars
9
Q
What is the mass of a low mass star?
A
- 0.5 - 10 solar masses
10
Q
What is the mass of a high mass star?
A
- > 10 solar masses
11
Q
Why do high mass stars have a shorter life?
A
- more mass means more GPE converted to KE
- results in a hotter core
- results in a higher rate of fusion
- shorter lifetime
12
Q
What happens as hydrogen runs out in the core of a high mass star?
A
- rate of fusion drops, radiation pressure drops
- gravitational collapse of star
- GPE —> KE, star heats up again
- fusion of helium starts in core
- fusion of hydrogen in outer shells starts
- outer shells expand and cool, emit red EM waves
- Red Super Giant
13
Q
What happens when the high mass star has an iron core?
A
- iron nuclei cannot be fused together
- star becomes unstable and implodes; supernova
- outer shells are shed
- dense core remains
- becomes black hole or neutron star
14
Q
When is a neutron star formed?
A
- mass of remaining core is less than 3 solar masses
- above Chandrasekhar limit
15
Q
What is a neutron star?
A
- composed entirely of neutrons
- high density
- low volume
- has a strong gravitational field
