Stellar Physics Flashcards
What is gravitational lensing?
The process by which large objects can cause light to bend.
Geodesic path
The shortest path between two points that light will always travel
Remember when drawing diagram for gravitational lensing
Draw apparent position above and below object curving spacetime
Hotter objects will emit _____ radiation per unit surface area at all wavelengths than cooler objects
More
Ideal black body
Absorbs and emits all frequencies perfectly
Luminosity equation
L=4pir^2õT^4
Where L is luminosity (Js^-1), r is the radius of the radiating object in m
õ is Stefan-boltzan constant (data sheet)
T is temperature (Kelvin)
What is luminosity equal to?
P, power in watts(w)
Apparent brightness equation
b = L/4pid^2
Where, b is apparent brightness in Js^-1m^-2
L is luminosity in Js^-1
and d is distance between observer and star (m)
Hertzsprung-Russel diagram - main sequence
Line with - gradient, our sun is in this group.
Most still fusing H to form He.
Hertzsprung- Russel diagram - red giants
Top right of diagram, fuse heavier elements together, have high luminosity, large radius but low surface temperature
Hertzsprung Russel diagram- white dwarfs
Bottom left of diagram, most are white, some blue, at end of life - fusion has stopped, high surface temperature, low luminosity and small radius
How are stars formed?
Stars are formed in interstellar clouds when gravitational forces overcome thermal pressure and cause a molecular cloud to contract until the core becomes hot enough to sustain nuclear fusion, which then provides a thermal pressure that balances the gravitational force.
Nebula
Huge clouds of dust where stars are born.
Stellar fusion reaction
Conversion of hydrogen to helium:
Step 1: H+H—> 2/1H + (e+) + v (electron neutrino and positron)
Step 2: 2/1H+H—>3/2He+ energy (in form of gamma rays)
Step 3: 3/2He+3/2He—>4/2He + 2(H)
What determines the lifetime of a star?
It’s mass
