5.5 Astrophysics and Cosmology Flashcards
What are nebulae
Gigantic clouds of dust and gas
What is a protostar
A very hot, very dense sphere of dust and gas
What is a main sequence star
A star in the stable phase of its life
Why is a main sequence star stable
Fusion has started causing it to be stable and in equilibrium
What conditions are required for nuclear fusion to occur
Extremely high pressures and temperatures inside the core to overcome the electrostatic repulsion between hydrogen nuclei in order to fuse them together to form a hydrogen nuclei
What is the balance of forces in a main sequence star
Gravitational forces act to compress the star but the estimation pressure from the photons emitted during fusion and the gas pressure from the nuclei in the core push outwards
What determines how long a star remains on the main sequence
The size and mass of its core
What’s a planetary satellite
A body in orbit around a planet
What are 3 characteristics of a planet
-a mass large enough for its own gravity to give it a round shape
-it has no fusion reactions
-it has cleared its orbit of most other objects
What is a solar system
What is a galaxy
A collection of stars and interstellar dust and gas
What is the universe
Our universe is everything
What’s the life cycle of a low mass star (0.5-10 solar masses)
Main sequence-> red giant -> white dwarf
Why does a star with a low mass remain on the main sequence for a longer time than a more massive star
The core of the star with a low mass is cooler than the core of a more massive star
How is a red giant formed
-reduction in the energy released by fusion in the core
-gravitational force is now greater than the reduced force from the radiation and gas pressure
-the core begins to collapse
-the core shrinks and the pressure increases enough to start fusion in a shell around the core
What are the properties of a white dwarf
-Very dense, volume of the earth
-no fusion reactions
-emits energy only because it leaks photons created in the earlier evolution
What is the Chandrasekhar limit
The maximum mass of a stable white dwarf star 1.44M
What is the electron degeneracy pressure
The pressure caused by the collapse of the star core under the force of gravity to prevent the core from further gravitational collapse
What is the life cycle of a high mass star (>10 solar masses)
Main sequence -> red supergiant -> supernova -> neutron star or black hole
What condition is required for a neutron star to be formed after supernova
If the mass of the core is greater than the Chandrasekhar limit, the gravitational collapse continues forming a neutron star
What condition is required for a black hole to be formed after supernova
If the core has a mass greater than about 3M, the gravitational collapse continues to compress the core
What is a black hole
A gravitational field so strong that in order to escape it an object would need an escape velocity greater than the speed of light
