topic 8 - Astrophysics Flashcards
what is a universe
a large collection of billions of galaxies
what is a galaxy
a large collection of billions of stars
what is our solar system
the Milky Way
why does gravitational field strength vary
- An object’s gravitational field strength depends on its MASS.
- The Moon has less mass than the Earth, so its gravitational field is much weaker.
how does gravitational force cause things to orbit
- there is an attractive gravitational force between any two objects– pulling them together. E.g. the planets and comets experience an attractive force towards the Sun.
- This gravitational force keeps them moving in curved paths called orbits. The Moon does not crash into the Earth, and the planets do not crash into the Sun because they are moving.
how do comets orbit
Comets have highly elliptical orbits, with the Sun at one focus. When they come in close to the Sun they speed up, due to the larger gravitational force on them.
how do moons orbit
Moons have circular orbits
how do planets orbit
in slightly squashed circles, called ellipses.
how to calculate orbital speed
(2 x π x orbital radius)/time period
v = 2πr/T
classification of stars
- classified by their colour
- colour emitted determines how hot they are
- red star is coolest (3000K)
- blue star is hottest (30000K)
what is a nebula
a giant interstellar cloud of gas and dust called a nebula bound together by gravitational forces
what is a protostar
- the force of gravity within a nebula pulls the particles closer together until a hot ball of gas forms, known as a protostar
- As the particles are pulled closer together the density of the protostar will increase
- This results in more frequent collisions between the particles which causes the temperature to increase
what is a main sequence star
- Once the protostar becomes hot enough, nuclear fusion reactions occur within its core
- Once a star initiates fusion, it is known as a main-sequence star
- During the main sequence, the star is in equilibrium and said to be stable
what is a red giant
- when the hydrogen causing the fusion reactions in the star begins to run out, the fusion reactions in the core will start to die down
- The star will begin to fuse helium which causes the outer part of the star to expand
- As the star expands, its surface cools and it becomes a red giant
what is a white dwarf
- Once the helium fusion reactions have finished, the star collapses and becomes a white dwarf
- the white dwarf cools down over time and as a result, the amount of energy it emits decreases
what is a black hole
when the core of the star is so massive, it collapses in on itself forming a void that nothing can escape
life stages of a smaller star
- nebula
- protostar
- main sequence star
- red giant
- white dwarf
life stages of a larger star
- nebula
- protostar
- main sequence star
- red giant
- supernova
- neutron star
- black hole
what is a supernova
- Once the fusion reactions inside the red supergiant cannot continue, the core of the star will collapse suddenly and cause a gigantic explosion called a supernova
- At the centre of this explosion, a dense body called a neutron star will form
- The outer remnants of the star are ejected into space forming new clouds of dust and gas (nebula)
what is a neutron star/black hole
- In the case of the most massive stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole
- A black hole is an extremely dense point in space that not even light can escape from
