Astrophysics And Cosmology Flashcards
What is a planet
An object that orbits around a star:
- With a mass large enough for its own gravity to give a round shape
- Has cleared its orbit of most other objects
- Does not undergo fusion reactions
What is a planetary satellite
A body in orbit around a planet e.g. Moons or satellites
What is a comet
Irregular bodies made of ice, dust and rock with highly elliptical orbits around the sun
Galaxy
A collection of starts and interstellar dust and gas. On average there are 10 billion starts in each galaxy.
What is the universe
Everything
What is gas pressure
The outwards pressure from a nuclei in the core of a star
What is radiation pressure
An outwards pressure caused from photons emitted in fusion
How is a protostar formed
As dust and gas in a nebula gets closer together gravitational collapse accelerates forming denser regions. These denser regions pull more gas and dust gaining mass and density. Gravitational potential energy is converted into kinetic energy then into temperature. This forms a protostar
How does a protostar become a main sequence star
Gravity pulls the gas in the protostar so tightly to the centre that pressure and temperature increases enough for fusion to occur.
How does a star remain in stable equilibrium
Gravitational force acts to compress the star but radiation pressure and gas pressure in the core pushes outwards
How does a low mass star become a red giant
- When a low mass star between 0.5-10M begins to lose fuel in the core, the gravitational force is greater than the radiation and gas pressure.
- The core begins to collapse increasing pressure for hydrogen to fuse into helium in the shell around the core.
- The star begins to expand.
How does a red giant form a white dwarf
Eventually most of the layers of the red giant drift off and forms a planetary nebula and the core remains as a white dwarf.
Characteristics a white dwarf
- High temperature
- Low luminosity
- High density
- Experience electron degeneracy pressure
What is electron degeneracy pressure
An outward force provided by electrons in a white dwarf which is caused by the Pauli exclusion principle
What is the Chandrasekhar limit
The maximum mass of a core of a star where electron degeneracy pressure will prevent gravitational collapse of the core. 1.44M
How does a high mass star become a red super giant
- In stars with a mass greater than 10 solar masses, when the hydrogen in the core runs low the core begins to collapse.
- The core of the star is hot enough for the fusion of helium, this causes the core of the star to expand, forming a red super giant.
- Core of the star is made up of a series of shells that fuse elements up to iron.
Why does a supernova happen and what is left behind after
- Iron nuclei cannot fuse as such a reaction cannot produce any energy. This cause the star to become unstable and the layers of the star implode.
- A black hole or neutron star will be produced
Characteristics of a black hole
- Created if the core has a mass greater than 3 solar masses
- Strong gravitational field
- High density
Characteristics of a neutron star
- Created is a the mass of the star is greater than the Chandrasekhar limit
- Made up of almost entirely of neutrons
- Small, can be 10km in diameter
- Similar density of an atomic nuclei
Hertzsprung-Russel diagram
A graph showing the relationship between luminosity and temperature in stars (increasing right to left)
Why are energy level negative
As external energy is required to remove an electron from an atom
What happens when electrons make a transition from a higher to lower energy level
A photon is emitted and electron loses energy
How is an emission spectra line produced
Electrons make a transition for a lower energy level emitting a photon with a specific wavelength
What is a continuous line spectrum
All visible frequencies are present
