Astrophysics SL Flashcards
apparent brightness (b)
amount of energy received per second per unit area by an observer (unit: Wm^-2)
astronomical unit (AU)
the mean distance from the centre of the Earth to the centre of the Sun (1.50 x 10^11m)
binary stars
two stars orbiting their common centre of mass
cepheid variable
a star that undergoes a periodic expansion of its outer layers that gives a periodic variation in its luminosity
Chandrasekhar limit
maximum star remnant mass (1.4M⊙) where electron degeneracy pressure prevents further gravitational collapse
constellation
a group of stars that appear to make a pattern in the sky but they may not necessarily be close to each other in space
cosmic microwave
background (CMB) radiation
radiation emitted by the universe consistent with a temperature of 2.7K
cosmic scale factor (R) (expansion)
gives a measure of the expansion that has taken place in the universe
dark energy
invisible energy source that may be accelerating the expansion of the universe
electron degeneracy
pressure
where electron repulsion prevents further gravitational collapse of a star
galactic cluster
a group of galaxies gravitationally bound together, orbiting around a common centre of gravity
galaxy
a large scale collection of stars, gas and dust held together by gravity
globular stellar cluster
symmetrically arranged stellar cluster of 10^4 - 10^5 old stars
Hertzsprung-Russell
diagram
graph plotting the luminosity of stars against their temperature
Hubble’s Law
the speed at which galaxies are moving away from Earth (recession speed) is directly proportional to their distance from Earth
L⊙ and M⊙
symbols for luminosity and mass of the Sun
light year (ly)
the distance light travels in one year
luminosity (L)
total amount of energy emitted per second by a star (unit: W)
main sequence star
a “normal” star that is fusing hydrogen into helium
nebula
intergalactic cloud of dust and gas
neutron degeneracy
pressure
where neutron repulsion prevents further gravitational collapse of a star
Newton’s model of the
universe
the universe is infinite in space and time, uniform and static
open stellar cluster
irregular shaped stellar cluster of several hundred young stars
Oppenheimer-Volkoff limit
maximum star remnant mass (3M⊙) where neutron degeneracy pressure prevents further gravitational collapse
parsec
distance at which the angle subtended by the radius of the Earth’s orbit is one arc-second
planetary nebula
the ejection of the outer layers of a small star (< 8M⊙) once fusion has stopped
planetary system
a group of planets orbiting a star
pulsar
a rotating neutron star
recession speed
the speed at which an object is moving away from an observer
red giant (and supergiant)
large (mass & surface area), relatively cool star, red in colour
redshift
apparent increase in the wavelength of light from distant galaxies due to their motion away from us
redshift ratio (z)
ratio of change in wavelength due to cosmological redshift to original wavelength emitted by a galaxy moving relative to Earth
singularity
point containing the entire universe at the start of the Big Bang
stellar cluster
a close group of gravitationally bound stars, gas and dust (within a galaxy)
stellar parallax
method used to measure distances to stars based on their apparent movement in position relative to distant background stars over a 6 month period
supercluster
a large grouping of galactic clusters
supernova
the ejection of the outer layers of a large star (> 8M⊙) once fusion has stopped
type Ia supernova
type of supernova with a known luminosity that occurs in binary star systems where one of the stars is a white dwarf
white dwarf
small (mass & surface area), relatively hot star, white in colour
cosmic scale factor (relative)
a measure of the relative size of the Universe
accelerating universe outcome
expansion continues at an increasing rate due to dark energy
type Ia supernovae (formation)
formed when a white dwarf in a binary system gains mass from its companion star and explodes due to fusion restarting
closed universe outcome
gravity causes the Universe to collapse back in on itself - the Big Crunch
open universe outcome
gravity slows expansion but is not strong enough to stop it
flat universe outcome
gravity slows expansion but takes an infinite time to do so
MACHOS
Massive Compact Halo Objects - high density compact stars at the ends of their lives
Jeans mass (Mj)
minimum mass required for a gas cloud to collapse and star formation to occur
r-process
neutron capture where there is not time for beta decay to occur before further neutron capture
s-process
neutron capture where there is time for newly formed nuclides to undergo beta decay and form a new element
CNO cycle
process by which hydrogen undergoes fusion to create helium in stars with a mass greater than four solar masses
proton-proton chain
process by which hydrogen undergoes fusion to create helium in the Sun
nucleosynthesis
process of forming different nuclides by nuclear fusion
type II supernovae
result from the rapid collapse and violent explosion of a massive star (> 8 solar masses)
density parameter (Ωo)
the ratio of the actual density of the Universe (ρ) to the critical density (ρc)
isotropic
the same in all directions
WIMPS
Weakly Interacting Massive Particles - subatomic particles
the Cosmological Principle
when viewed on a large scale, the Universe is homogenous and isotropic
