Chapter 19 - Stars Flashcards
Define Nebulae
A gigantic cloud of dust and gas (mainly hydrogen)
Define Planets
An object that has a mass large enough for its own gravity to give it a circular shape. It has no fusion reactions and has cleared its orbit of most other objects.
Define Dwarf planets
They have not cleared their orbit of other objects.
Define Asteroids
Small, irregularly shaped bodies, composed of dust and metals. There have near circular orbit around stars and don’t contain any ice.
Define Planetary satellites
A body in orbit around a planet.
Define Comet
Small irregular bodies made up of ice, dust and small pieces of rock. They all orbit the Sun, in highly eccentric elliptical orbits.
Why do comets have ice?
They are so far away from the Sun that the ice doesn’t melt due to the lack of heat.
Define Solar system
The gravitational bound system of the Sun, and all the planets that orbit it.
Define Galaxies
A collection of stars, planets and interstellar dust and gas.
Define Protostar
A very hot, very dense sphere of dust and gas.
Star Birth
Nebulae form when tiny particles of dust and gas come together due to the force of gravitational attraction.
The denser regions of a nebula pull in more matter, becoming hotter as the gravitational potential energy is transferred to heat energy.
A protostar forms in the nebula.
Star from a protostar
Extremely high pressures and temperatures in the core will overcome the electrostatic forces of repulsion between hydrogen nuclei to fuse them together to form Helium nuclei.
Nuclear fusion of hydrogen nuclei begins and the protostar will become a main sequence star.
What does a fusion reaction produce
Energy in the form of kinetic energy
Star life
Once a star is born, it’ll stay the same size.
This is because the gravitational forces are equal to the radiation pressure and the gas pressure, meaning they’ll remain in equilibrium.
What is a star’s stable phase called
Main sequence.
What does a star with a low mass have as a consequence
A cooler core
What is a star with a low mass
0.5 Mo. to 10 Mo. They will turn into red giants.
Red giants
Energy is released by fusion will decrease, meaning the G.F increases. So the core will collapse, and the pressure increases. So, the fusion happens in a shell around the core. This means the periphery will expand, as the layers move away from the core.
What is a Mo.
The mass of the sun.
1.99 X 10^30 kg.
Why do red giants have an inert core?
So fusion doesn’t happen.
Because the temperature is too low.
What happens when the layers cool
It gives the red colours
White dwarf
It’s very dense.
There are no fusion reactions and it leaks photons created at an earlier evolution.
The Pauli Exclusion
2 electrons cannot exist in the same energy state.
Electron Degeneracy Pressure
When the core of a star collapses under the force of its own gravity, all the matter is forced together into a smaller volume. However, electrons aren’t allowed to occupy the same energy levels in an atom, so the atoms can’t move too close to each other. Therefore, a pressure s exerted by the electrons as the star collapses, which is called the electron degeneracy pressure.
The pressure outwards counters the gravitational attraction inwards, so that the core can’t continue collapsing.
Chandrasekhar Limit
The EDP will exist if the core has a mass less than 1.44 Mo. This limit is the max mass of a stable white dwarf star.
More massive stars
They have a mass greater than 10 Mo.