astrophysics Flashcards
the universe:
-a large collection of billions of galaxies
a galaxy:
-a large collection of billions of stars
solar system:
-a collection of planets orbiting a common star
-our solar system is in the Milky Way galaxy
gravitational field strength: (now that this makes everything orbit)
-> the force per unit mass on a body in a gravitational field
-measured in Newtons per kilogram (N/kg)
-it varies with the mass and size of the body and is different on other planets and the moon compared to earth (on earth: 10 N/kg)
-weight = mass x gravitational field strength W=mg
Moons and orbits:
-Moons orbit planets
-The orbits are slightly elliptical with near constant orbital speed
Planets and comets:
-Planets and comets orbit the Sun
-the orbits of planets are slightly elliptical with near constant orbital speed
-the orbits of comets are highly elliptical
-made of ice (usually)
-closest to the sun = fastest
-farthest to the sun = slowest
artifical satellites:
-artificial satellites (human made) orbit the earth
-the greater the orbital radius the smaller the time period, the greater orbital speed
-orbital speed = 2 x π x orbital/time period, v = 2πr/T
how to classify stars:
(hottest) blue, blue-white, white, white-yellow, orange, red (coldest)
life cycle of Solar Mass Stars
stellar nebula -> average star -> (main sequence star) -> red giant -> planetary nebula -> white dwarf
life cycle of Larger Stars
stellar nebula -> massive star -> (main sequence star) -> red supergiant -> supernova -> neutron star or black hole
gravity:
-isaac newton published his theory of gravity
-depends on: masses of 2 objects + distance between the 2 objects
-distance gets greater = gravity decreases
-mass increase = gravitational force is stronger
planets:
8 - planets
-Mecury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
-planets that are the furthest from the sun feel the weakest pull and follow the least curved path
-planets that are closest to the Sun feel the greatest attraction and so follow the most curved paths
nebula:
-all stars form from a giant cloud of hydrogen gas + dust
protostar:
-the force of gravity pulls the dust + gas together to form a protostar
-the temp- rises as the star gets denser and more particles collide with each other
-when the temp. gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei
-this gives out a huge amount of energy, which keeps the core of the star hot = star is born
main sequence star:
-the star enters a long stable period. during this period, the outward pressure cuased by thermal expansion balances the force of gravity pulling everything inwards
-in this stable preiod it’s called a main seuqence star and it typically lasts several billion years
-the heavier the star, the shorter the time in the main sequence (the sun is in the middle of this stable period)
red giant:
-eventually the hydrogen in the core begins to run out and the force due to gravity is larger than the pressure of thermal expansion
-the star is compressed, until it is dense and hot enough that the energy (and so pressure) created makes the outer layers of the star expand
-the star becomes a red giant (if it is a small star) or a red supergiant (if it is a larger star)
-it becomes red because the surface cools
white dwarf:
- a small to medium sized star like the Sun becomes unstable and ejects its outer layer of dust and gas. This leaves behind a hot, dense solid core - a white dwarf
supernova:
-big stars, however, start to glow brightly again as they undergo more fusion to make heavier elements
-the expand and contract several times, as the balance shifts between gravity and thermal expansion
-eventually, the explode in a supernova
neutron star:
-the exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a nuetron star
-if the star is massive enough, it will collapse and become a black hole - a super dnese point in space that not even light can escape from
