OP- D Astrophysics Flashcards
apparent brightness
amount of energy received per second per unit area by an observer (Wm-2)
astronomical unit
the mean distance from the centre of the Earth to the centre of the Sun
(1.50 x 10^11)
binary stars
two stars orbiting their common centre of mass
three types of binary stars
- visual: can see two distinct stars
- eclipsing: periodic variation of brightness
- spectroscopic: change in wavelength of light receive from star (Doppler effect)
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 (1.4Ms) where electron degeneracy pressure prevent further gravitational collapse
constellation
a group of star that appears 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 constituent with s temperature of 2.7K
cosmic scale factor (R)
gives a measure of the expansion that has taken place in the universe
dark energy
invisible energy source that my 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 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 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
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 outer layers of a small star (< 4M⊙) once fusion has stopped
planetary system
a group of planet 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
- late stage in a star’s life cycle
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 the Doppler effect 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
- final stage for a small star
- no longer fusion, cooling down
