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Apparent Brightness
What two things does the apparent (or perceived) brightness of an object depend on?
How can this relationship be used to determine distances?
Apparent Brightness α Luminosity/Distance^2
Creating the Heavy Elements
How are the lives and deaths of stars related to the creation (and distribution) of the heavy elements?
What is the heaviest element that can be created in the core of a star?
Stellar Deaths and the Creation of Heavier Elements
A star will fuse heavier and heavier elements until:
1) It can no longer achieve the core temperature needed to fuse heavier elements (low mass stars)
or
2) Iron is created in the core (highest mass stars)
What is left behind when a low mass star dies?
Red Supergiant
Stellar Lifetimes
Is the lifetime of a high mass star shorter or longer than that of a lower mass star?
Evolution of Stars > 8 MSun
Higher mass stars evolve more rapidly (=> shorter lifetimes).
Heaviest element made is iron.
Products of outer layers become fuel for inner layers
Eventual state of > 8 MSun
star
Stellar Explosions
Novae
Accreting white dwarf in a binary system
How is this process related to a carbon-detonation supernova?
What is the Chandrasekhar limit?
A Carbon-Detonation Supernova
Despite novae, mass continues to build up on white dwarf (WD).
If mass grows to 1.4 MSun
(the "Chandrasekhar limit"), gravity overwhelms the Pauli exclusion pressure supporting the WD.
This starts carbon fusion everywhere at once.
Tremendous energy makes star explode. No core remnant.
Death of a Very High-Mass Star
M > 8 MSun
Iron core at T ~ 1010 K radiation photodisintegrates iron nuclei into protons and neutrons.
Absorbs enormous amount of energy => core collapses in < 1 sec.
Result is a Core-collapse Supernova
What is left behind?
Testing our Theories
Why are star clusters useful for stellar evolution studies?
1) All stars in a cluster formed at about same time (so all have the same age)
2) All stars are at about the same distance3) All stars have same chemical composition
The only variable property among stars in a cluster is mass!
1. White Dwarf If initial star mass < 8 M
Sun or so. (Low Mass)
2. Neutron Star If initial mass > 8 M
Sun and < 25 M
Sun . (Intermediate Mass)
3. Black Hole If initial mass > 25 M
Sun . (High Mass)
Final States of a Star
Neutron Stars
Conservation of Angular Momentum => Fast Rotation rate: few to many times per second.
Huge Magnetic field: 1012 x Earth's!
What type of object can these conditions produce?
A neutron star over the Sandias?
Black Hole Geometry
What is the “surface” of a black hole called?
What physical property determines it's size?
Event horizon: imaginary sphere around object with radius equal to Schwarzschild radius (determined by mass). “Surface” of black hole.
Event horizon
Schwarzschild Radius
According to Einstein's General Relativity, all masses curve space.
How does this change our understanding of the gravitational force?
Effects around Black Holes
Near event horizon:
1) Enormous tidal forces.
2) Bending of light.
2) Gravitational redshift.
3) Time dilation.
The Equivalence Principle
What two phenomenon did Einstein show produce effects that are indistinguishable from one another?