Astrophysics and Cosmology Flashcards
Nuclear fusion
The process of two nuclei joining together and releasing energy from a change in binding energy
Galaxy
A cluster of millions or billions of stars
Stars
Are formed when huge amounts of matter, gas or interstellar dust are pulled together under the force of gravity
Planet
Bodies that move in elliptical orbits around stars to form a solar system
Planetary satellites
Smaller bodies than planets can orbit them, these bodies are called planetary satellites. An example is the moon
Gravitational collapse
The inward movement of material in a star due to the gravitational force caused by its own mass
Radiation pressure
Due to the momentum or photons released in fusion reactions
Gas pressure p
Is related to temperature and volume using pV =nRT
A main sequence star
A star in the main part of its life cycle, where it is fusing hydrogen to form helium in its core
A red giant
A star in the later stages of its life that has nearly exhausted the hydrogen in its core and is fusing helium nuclei.
A white dwarf
The end product of a low mass star. Very dense with a high surface temperature and low luminosity
Planetary nebula
An expanding, glowing shell of ionised hydrogen and helium ejected from a red giant star at the end of its life
Electron degeneracy pressure
The pressure that stops the collapse of a low mass star, this prevents a white dwarf from collapsing
Chandrasekhar limit
The maximum possible mass for a stable white dwarf star. It is equal to 1.4 times the mass of our sun. White dwarfs above this mass will collapse further to become neutron stars or black holes
Luminosity
The total energy emitted per second
Hertzsprung-Russell diagram
A luminosity-temperature graph
Supernova
The huge release of energy
Wien’s displacement law
λmax *T = constant. It is used to estimate the peak surface temperature of a star from the wavelength at which the stars brightness is maximum
Stefans law
Relates the luminosity of a star with its absolute temperature
T = 4πr^2σT^4
Astronomical unit (AU)
The mean distance from the centre of the Earth to the centre of the Sun
The parsec
A unit of distance that gives a parallax angle of 1 second of arc (1/3600 of a degree)
Stellar parallax
The apparent shifting of a star viewed against a background of distant stars when viewed from different positions of Earths orbit
Doppler effect
The change in wavelength caused by the relative motion between the wave source and an observer
Δλ/λ=Δf/f = v/c
Red shift
The apparent increase in wavelength of electromagnetic radiation caused when the source is moving away from the observer
Blue shift
The apparent decrease in λ of electromagnetic radiation caused when the source is moving towards the observer
Hubbles law
The recessional velocity of a galaxy is directly proportional to its distance from Earth
Hubble constant
The constant of proportionality in v =H.d
Cosmic background radiation
Microwave radiation received from all over the smh originating from after the Big Bang, when the universe cooled to 3000K. As the universe expanded, this is now just a faint microwave
The Big Bang theory
The universe started as an infinitely small, dense and hot point then expanded to what it is now. Time and space were both created at the instant of the Big Bang
The cosmological principle
The universe is:
•isotropic (The same in all directions)
•homogenous (of uniform density)
•subject to the same physical laws everywhere
Dark matter
Matter that cannot be seen and that does not emit or absorb electromagnetic radiation.
We know of its existence because of the expected mass of galaxies being so small compared to the actual
Dark energy
A type of energy that permeates the whole universe and opposes the attractive force of gravitation between galaxies via the exertion of negative pressure.
We predicted its existence because of the accelerating expansion of the universe opposing gravity
