Astrophysics Terminology SL Flashcards
solar system
collection of planets, moons, asteroids, comets, and other rocky objects in elliptical orbit around the sun
asteroids
rocky objects orbiting the sun
comets
irregular objects of ice, rock, and dust orbiting the sun
nebula
enormous cloud of dust and gas where stars often form
binary stars
two stars that rotate about a common center of mass
stellar cluster
group of stars close enough to be held together by gravity
open cluster
several hundred stars younger than ten billion years that still contain gas and dust
global cluster
stars older than 11 billion years containing little gas and dust
constellation
pattern formed from stars, not held together by gravity
galaxy
stars, gas, and dust held together by gravity containing billions of stars
spiral galaxies
disc shape with spiral arms spreading out from a central galactic bulge that contains the greatest density of stars
spiral arms
many young blue stars, gas, and dust
irregular galaxies
shapeless and can be stretched in the presence of other bigger galaxies
light year
distance traveled by light in one year ( 1ly = 9.46 x 10^15 m )
astronomical unit
average distance between the sun and earth (au) 1au =1.50 x 10^11m – approximately 8mins
parsec
(pc) most commonly used distance in astrophysics 1pc = 3.26 ly = 3.09 x 10^16m
stellar parallax
the star’s apparent shift of position of any nearby star against the background of distant stars – which can be used to measure the distance of stars from us
luminosity
the energy emitted by the star per second in watts – amount of light emitted from the stars surface
brightness
watts per square meter (Wm^-2) – how bright the star appears to be from earth
black bodies
theoretical objects that absorb all radiation incident upon them. perfect emitters for radiation, emitting the maximum radiation possible at their temperature
black body radiation
all objects with temperatures above absolute zero emits this
cepheid variables
highly luminous stars with regular and predictable changes in luminosity due to its cycle
What is the cycle of a cepheid star?
- Layer loses hydrostatic equilibrium and compresses inwards
- The star becomes less transparent
- The star heats up and internal pressure increases
- The layer of the star is pushed outwards, therefore, the star expands
- The layer cools and becomes less dense
- The radiation escapes and the pressure inside the star decreases. – The cycle then repeats
Hertzsprung-Russell diagram
depicts the relationship between the luminosities and temperatures of the stars (memorize the groups of stars on that diagram)
red giant stars
Cooler stars that emit less energy. They have higher luminosities and a larger surface area/diameter compared to the sun
Supergiant stars
Gigantic, bright stars that emit more energy with a larger surface area/diameter compared to the sun
White dwarfs
Remnants of old stars that are hot and dense. They have low luminosity and a small surface area
Main sequence star
Any star that fuses hydrogen in its core and has a stable balance of outward pressure due to nuclear fusion. Gravitational forces push inwards. – hotter and bigger stars w/ a finite life time
hydrostatic equilibrium
pressure due to gravitational attraction of inner shells is equal to the thermal and radiation pressure acting outwards
electron degeneracy pressure
resistance a densely patched gas of electrons exerts against further compression – this prevents the collapse of celestial objects
supernova
when a star collapses and the neutrons come close to each other. the outer layers of the star rush toward the core but then explode. the remnants are the neutron stars
neutron degeneracy pressure
pressure of a neutron star that resists further gravitational collapse into a black hole
Oppenheimer-volkoff limit
the upper value of a neutron star where neutron degeneracy resists further collapse of a black hole
black hole
a region of space having a gravitational field so intense that no matter or radiation can escape
local redshift
occurs within galaxies or clusters, when movement causes the wavelengths emitted to be longer
blue shift
when movement causes the wavelengths emitted to be shorter
cosmological redshift
the larger scale of local redshift that is associated with the expansion of the universe. Light travels through the expanding space thus its wavelength is stretched
solar mass
standard unit of mass in astronomy – the approximate mass of the sun ( 2 x 10^30 kg )
What is the period-luminosity law for the Cepheid stars?
It’s the relationship between the pulsation period of a cepheid star and its luminosity. The brighter the star, the slower it pulses.
Chandrasekhar mass limit
Approximately 1.4 times the mass of the sun – determines whether a star will form a white dwarf or a neutron star
If the mass of the remnant core after the red giant phase is < mass limit, it will become a white dwarf
If the mass of the remnant core > mass limit, it will become a neutron star or black hole
hubble’s law
the velocity that galaxies are moving away from us is directly proportional to their distance from us – the further away the galaxy is, the faster it is moving away
