Astrophysics Flashcards
what can we say about a planet orbiting furthest away from the sun
- it travels slower the further away from the sun it is therefore it takes the longest time to orbit
how do the colours of planets relate to their temperatures
a red star is the coolest
a blue star is the hottest
how do astronomical objects heat up or cool down
they cool as they expand
and heat up as they contract
what are the 5 steps in the life cycle of a star with a similar mass to our sun
- nebula
- protostar
- main sequence star
- red giant
- white dwarf
what is a nebula
the first in the life sequence of a star
a giant cloud of hydrogen and dust
how is a protostar formed
- the force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas known as a protostar
as the particles are pulled closer together the density of the protostar will increase, this will result in more frequent collisions which cause temperature to rise
how do main sequence stars start to be produced
- once the protostar becomes hot enough, nuclear fusion reactions occur in its core —-> the hydrogen nuclei will fuse to form helium nuclei and every reaction releases heat energy which keeps the core hot
why are main sequence stars stable
- thermal expansion (due to fusion reactions) occurs within its core while the force of gravity keeps the star in EQUILIBRIUM
(the inward force of gravity is equal to the outward pressure from thermal expansion)
why do stars transition from main sequence to red giant
because the hydrogen causing the fusion reactions starts to run out, so the reactions will start to die down
this causes the core to shrink (because the force if gravity is greater than the thermal expansion now) and heat up —> as he core shrinks, more reactions will cause the outer part of the star to expand —-> the new reaction: eg helium will undergo fusion to for beryllium
therefore it will become a red giant because it is expanding and it is red because the outer surface starts to cool
how are white dwarfs formed
the star will eventually become unstable and eject the outer layer of dust and gas
the core which is left will collapse completely due to the pull of gravity and become a white dwarf
the white dwarf will start cooling down and so slowly the amount of energy it emits will decrease
what is the life sequence for a star with a much larger mass than our sun
- nebula
- protostar
- main sequence
(^^all same as mass smaller than sun^^) - red supergiant
(^^described in the exact same way as a red giant^^) - supernova
- neutron star or black hole
how are supernovas formed (for stars with a mass more than out sun)
- once the fusion reactions in the red supergiant finally finish, the core will collapse suddenly causing a gigantic explosion called a SUPERNOVA
at the centre of the explosion a dense body called a neutron star is formed
the outer remnants of the star will be ejected into space
how is a neutron star or a black hole formed
in the centre of the supernova explosion a neutron star is formed
in the case of the largest stars the neutron star will collapse under the force of gravity until it becomes a black hole
what is a black hole
an extremely dense point in space that not even light can escape from
what is the absolute magnitude of a star
the brightness of a star at a standard distance
what is the scale for absolute magnitude
the brighter the star, the smaller the magnitude
the dimmer the star, the larger the magnitude
on a hertzsprung-russel diagram describe the location of the main sequence, red giants and white dwarfs
main sequence \
red supergiants above red giants in top right
white dwarfs bottom left
what is a hertzsprung-russel diagram
a way of classifying stars
luminosity or absolute magnitude (dim at the bottom [highest number] and bright at the top [lowest number]) against temperature (hot on the left, cool on the right)
what is the big bang theory
that the universe began from a very small region that was extremely hot and dense, then there was a giant explosion called the big bang which caused the universe to expand from a single point
evidence of the big bang
- galactic red shift
- cosmic microwave background radiation
why is galactic redshift evidence for the big bang theory
by observing the LIGHT SPECTRUMS from supernovae in other galaxies, there is evidence that they are moving away faster than nearby galaxies (because during an explosion some matter will be lighter and travel at a greater speed, further from the source of the explosion and some will travel at a slower speed, heavier, closer)
-> redshift because the lightwaves are becoming elongated by the movement away
if you went back in time and traced the galaxies backwards hey would all eventually meet at a single point
