Astrophysics SL

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order of solar system
(asteroid belt)
stellar cluster
grouping of large stars that have gravitational interaction/attraction with each other and are relatively close to one another
binary star
two stars orbiting a common centre
black dwarf
the remnant of white dwarf after it has cooled down
very low luminosity
black hole
a singularity in space time
the end result of the revolution of a very massive star
cepheid variable
a star of variable luminosity with well-defined period
the period is related to the absolute luminosity of the star and so can be used to estimate the distance to the star
a group of stars in a recognizable pattern that appear to be near each other in space when observed from the earth
dark matter
matter that is too cold to radiate
its existence is inferred from techniques other than direct visual observation
collection of very large number of stars mutually attracting one another through the gravitational force and staying together
main-sequence star
a normal star that is undergoing nuclear fusion of hydrogen to helium
neutron star
the end result of the explosion of a red supergiant
a very small star with high density
star consist almost entirely of neutrons, hence its name
planetary nebula
the ejected envelope of a red giant star
red giant
a main-sequence star evolves into a red giant
there are nuclear reactions involving the fusion of helium into heavier elements
white dwarf
the end result of the explosion of a red giant
small, dense star in which no nuclear reactions take place
although hot, small size gives very low luminosity
power radiated by a star
apparent brightness
received power per unit area
change in position of a star in the sky at times six months apart
Wien displacement law
higher the temperature, the lower the wavelengths at which most of the energy is radiated
standard candles
a star of known luminosity

*period can be used to find luminosity, which can then find apparent brightness, which finds distance. hence, relative distance can be measured using standard candles.

Chandrasekhar limit
mass at which electron degeneracy pressure prevents the further collapse of the core, star will become a stable white dwarf
Oppenheimer-Volkoff limit
mass at which star can maintain stability and become a neutron star
Hubble’s law
velocity of recession is directly proportional to distance
more distant the galaxy, the faster it moves away from us
apparent magnitude
relative brightness as seen from the earth
absolute magnitude
relative brightness as seen 10 pc from the star
critical density
amount of matter per unit volume space that could create enough gravitational pull so that the universe will continue to expand, yet slow down to a certain point
how do we know that main sequence stars are made predominantly of hydrogen?
emission spectrum of the star contains being absorbed by
cosmic microwave background radiation
1. it does not come from any particular spot in the sky but rather fills all space
2. radiation detected was remnant of the hot explosion at the beginning of time
* When the universe is expanding, it gave off EM waves and these waves have become thin wavelength as the space-time expands to the present time
rocky substance that orbits around the sun
red shift
red-shift is a result of Doppler effect and proves that universe is expanding and galaxies are moving away. therefore universe is not static.
Newton’s model of the universe
infinite, uniform, static
stellar parallax method
if angular position of a star is measured before and after 6 months, the two position will be different relative to a background of a very distant star.
Olber’s paradox
if universe is infinite, there will be infinite amount of energy. but if the universe is uniform, then each point will receive infinite energy uniformly therefore the sky will be bright.
a small body made of mainly ice and dust, orbiting the sun in an elliptical orbit
displays atmosphere when close to sun but atmosphere no longer present when far from sun
Categories: Astrophysics