Unit 3 Evolution of Stars Flashcards
How are stars formed?
Stars are formed from huge gravitational collapses of clouds of dust up to 15 kpc across. These clouds may contain enough raw materials for several thousand stars.
What is an emission nebula?
An emission nebula is a glowing cloud of gas that has been excited by newly-formed stars. Eg: Orion’s Nebula.
What is a protostar?
Once the gas of the nebula starts to collapse it breaks up into smaller collapsing knots called protostars.
What is a main sequence star?
Once a protostar reaches a central temperature of 15 million K (the temperature required for nuclear fusion of hydrogen to helium) and becomes stable the star is now a main sequence star.
How long can a main sequence star be stable for?
Anything from 100 million years to 1 million million years.
How does a red giant or supergiant form?
When the hydrogen core runs out of fuel in a main sequence star fusion takes place in the new outer layers of helium. The star expands and cools becoming a red giant or supergiant.
What is a planetary nebula?
When a red giant loses its outer layers in an expanding shell of gas. A hot white dwarf is found at the centre with a mass similar to that of the Sun, but a size similar to that of the Earth.
What is a supernova?
When a large mass supergiant has fussed elements up until iron there is a violent explosion called a supernova where layers are blown away at speeds up to 5000 km/s.
What are the remains of a supernova?
The remains are called a supernova remnant which can either be a neutron star or a black hole.
What is a neutron star?
A neutron star is a star with slightly more mass than the Sun but a diameter of 20 km. The high density means it has a very strong gravitational effect and rotates very rapidly on it’s axes.
What is a pulsar?
The strong pulses of radio waves emitted form a neutron star at it’s poles where it spins.
What are black holes?
Black holes are formed when a star three times as massive as the Sun goes supernova. They have very high densities and gravitational pulls that mean electromagnetic radiation cannot even escape. It is not possible to detect a black hole directly, however we can detect accelerating X-rays which are emitted by accelerating matter from a nearby binary system.
What are absorption lines?
Lines/gaps in the spectrum where light has been absorbed by certain chemicals.
What is the Harvard System?
The scheme of letters that classify a star’s spectral type. The letters O, B, A, F, G, K and M, which can be remembered by the mnemonic “Oh Be A Fine Girl Kiss Me!”.
What is the Hertzsprung-Russell diagram?
The diagram that shows that stars fall into 4 distinct groups: Main sequence stars Red giants Supergiants White dwarfs
