Week 6 Energy Generation and Stellar Remenants Flashcards
what is the PP cycle
The nuclear fusion in a star takes place when 4 H atoms collide to produce a He atom. The mass deficit of the collision is released as energy
why is nuclear fusion in the star bizarre
normally fusion is very unstable but it is able to remain stable in a star for a long time because the star the PP cycle is very slow and the star produces just enough to remain in hydrostatic equilibrium
how does the nuclear reaction rate relate to temperature
the rate is extremely sensitive to temperature
a higher reaction rate causes a higher temp which in turn causes a higher reaction rate.
why is hydrostatic equilibrium important in stars
it helps to control the nuclear reaction so that it doesn’t spiral out of control
what is the Stellar thermostat
the idea that as you add energy the star heats up and then cools itself down to remain at a relatively constant temperature
what are the 2 reasons more massive stars produce more energy
Virial theorem requires higher temp
Fusion occurs much faster
what is the stellar life time equation
t = fM / L
f is the efficiency factor
L is the luminosity
what happens when a star runs out of Hydrogen fuel
hydrogen fusion stops and the star’s core begins to contract whilst the temperature increases until the conditions for fusion of Helium are met and the star uses Helium as a new fuel
what happens when a star runs out of Helium fuel
Helium fusion produces less energy than hydrogen runs out quickly and the stars core again contracts and heats up burning through other elemental fuels until it reaches Iron
what happens when a star’s core has to use iron as a fuel
fusion can no longer take place so the iron core implodes. this implosion leads to a supernova
what are the two possible outcomes of a supernova
the star either becomes a neutron star or if it is large enough a black hole
why do some stars become white dwarfs
they aren’t massive enough to reach iron so stop fusion at carbon imploding earlier
what is the Schwarzschild radius and its equation
it is the radius a star of mass M has to have to become a black hole
R = 2GM / c^2
