D. Astrophysics (AHL) Flashcards
Jeans criterion
For a gas cloud to collapse into a star the gravitational potential energy of the particles must be greater than the kinetic energy.
Jeans mass
This mass a cloud must be to form a star under certain conditions.
Proton proton chain
How H is fused to He
Triple alpha process
Fusion of He to beryllium and the to carbon
Neutron capture
The process where a nucleus absorbs a neutron which, if there is sufficient time, can decay by beta minus into a proton, making a heavier element.
S-process
Neutering capture with a low neutron flux (eg in star) so beta decay can happen and heavier elements can be made.
R-process
Neutron capture with a high neutron flux so there is insufficient time for beta decay so heavier isotopes are made.
Type IA supernova
When a dense dwarf star in a binary system gains enough mass from the other star to cross the Chandrasekhar limit, meaning it collapses.
Type II supernova
When a massive star has fused all its silicon into iron so has no radiation pressure and collapses.
Difference between IA and II supernovae
Brightness of IA falls sharply whilst it plateaus for a few days for type II.
Cosmological principle
The universe is isotopic and homogenous
Isotropic
Same in all directions
Homogenous
Same in all locations
Dark matter
Matter that does not interact with light thought to make up around 25% of the energy density of the observable universe.
Dark energy
Energy causing the expansion of the universe to accelerate.
