Equilibrium in Stars Flashcards
All 6 cards in this deck
What is a nebula?
A cloud of dust and gas (mostly hydrogen) in space, from which stars form.
What are the steps by which a nebula produces the conditions needed for nuclear fusion?
e.g. the cloud of gas and dust that formed the Sun
- The nebula collapses under gravity
- Gravitational potential energy is transferred to kinetic energy of the particles, so temperature and pressure rise
- Very high temperature and pressure start hydrogen fusion in the protostar
What is a protostar?
A collapsing cloud of gas and dust that is heating up but has not yet begun nuclear fusion.
Which two effects are balanced in a stable (main sequence) star?
Inward gravity and outward thermal expansion (radiation pressure) from fusion in the core.
True or false? A main sequence star stays the same size because gravity is the only force acting on it.
False. It stays the same size because inward gravity is balanced by the outward thermal expansion caused by fusion.
What happens to the balance in a star when the hydrogen in its core begins to run out?
Fusion in the core slows, so outward thermal expansion no longer balances gravity; the core contracts and the outer layers expand.