Astro Mid Term Sem. 2 (Book 4/7) Flashcards
What is the life of a HIGH mass star? (Diagram in book 4 bottom of page 1)
- Interstellar cloud
- Protostar
- Massive Star
- Pulsating Yellow Giant
- Red Giant
- Supernova explosion
- Black Hole or Neutron Star
How do HIGH MASS STARS make the elements necessary for life?
- Big Bang made 75% Hydrogen and 25% Helium, stars made everything else
- Helium Fusion can make Carbon in low-mass stars
- Carbon can fuse into Nitrogen and Oxygen
- Carbon also into Oxygen, Neon and Magnesium
What is Helium Capture?
High core temps. allow Helium to fuse with heavier elements
What is Advanced Nuclear Burning?
When core temps. in stars with > 8 M(sun) allow fusion of heavy elements ending with Iron
- Advanced reactions make heavier elements
- Iron is a dead end for fusion because nuclear reactions involving iron do not release energy
What is the structure of an Evolved, Massive Star? (chemically)
- H -> He -> C -> O -> Si (silicon) -> Fe (Iron)
- When Helium is depleted, fusion of heavier elements begins. This process is called Neucleosynthesis
- Iron does not burn - collapse of the star’s iron core and the explosion of the stars outer envelope
What is the structure of an Evolved, Massive Star? (chemically)
- H -> He -> C -> O -> Si (silicon) -> Fe (Iron)
- When Helium is depleted, fusion of heavier elements begins. This process is called Neucleosynthesis
- Iron does not burn - collapse of the star’s iron core and the explosion of the stars outer envelope
Advanced Nuclear Burning occurs in multiple shells. Name the elements burnt in each shell starting at the core.
1) Inert Iron core
2) Silicon fusion
3) Magnesium Fusion
4) Neon fusion
5) Oxygen fusion
6) Carbon fusion
7) Helium fusion
8) Hydrogen fusion
9) Nonburing hydrogen
High Mass Stars become what after core hydrogen runs out?
They become Supergiants
- Luminosity doesn’t change much but radius gets far larger
Check diagram in book 4 middle of page 4
- Iron builds up in core until degeneracy pressure can no longer resist gravity
- The core suddenly collapses, creating Supernova explosion
When does fusion stop in a Supergiant?
- Fusion stops with iron and a star with an iron core is out of fuel. Iron atoms cannot fuse and release energy
- The core collapses due to reduced pressure converting the iron core into mostly neutrons. The electrons get pushed into the nuclei, with protons they form neutrons
- The core pressure then surges and lifts the outer layers from the star in a titanic explosion - a Supernova
Energy and neutrons released in Supernova explosion enable WHAT elements to form?
It enables elements heavier than iron to form, including Au (gold) and U (uranium)
99% of Supernova energy is emitted as what? What happens to the other 1%?
- It is emitted as neutrinos
- 1% is converted into the kinetic and heat energy of the ejecta (i.e., outer gas layers)
99% of Supernova energy is emitted as what? What happens to the other 1%?
- It is emitted as neutrinos
- 1% is converted into the kinetic and heat energy of the ejecta (i.e., outer gas layers)
What is a Neutron Star? What are its characteristics?
- Neutron Stars are similar to giant atomic nuclei the size of a city
- Neutron Stars typically have masses up to 3 solar masses and diameter of approximately 10 Km
How to Neutron Stars form?
- Gravity overwhelms pressure in the star’s iron core when the core’s mass grows to about 1.4 solar masses
- Result: collapse of the core + release of an enormous amount of energy
- Electrons and protons in the remnant are squeezed together to form neutrons and neutrinos
