14 Stellar Evolution Flashcards
What are Nebulae?
Nebulae are large interstellar clouds of dust and gas
What are open clusters?
Open clusters are a group of young stars that formed from the same giant molecular cloud. They all are roughly the same age
What are Globular Clusters?
Globular clusters a group of older stars
Where are open clusters found?
Open clusters are found on the spiral arms of the Galaxy
Where are globular clusters found?
Globular clusters are found in a ‘halo’ around the centre of the galaxy
What is the Messier Index?
The Messier Index is a catalogue of 110 astronomical objects that can be observed
How are all stars first originally formed?
All stars originate from the gravitational collapse of of a cool, dense molecular cloud of gas and dust that are found in the spiral arms of galaxies. As the cloud collapses, it becomes unstable and fragments into smaller clumps (protostars) that will form the cores of individual stars
What happens when a protostar collapses?
Gravitational potential energy is converted into kinetic energy and its temperature increases. It eventually becomes hot enough for the fusion of hydrogen into helium.
What is radiation pressure?
Radiation Pressure is the pressure that is exerted on a surface due to the exchange of momentum between an object and the electromagnetic field. The Radiation Pressure of stars is caused by the nuclear fusion of elements
What happens during the main sequence stage?
During the main sequence stage, radiation pressure and gravity balance. This stops any further gravitational collapse
How long is a star in the main sequence stage?
A star is in the main sequence stage for ~90% of its lifetime
What is the Chandrasekhar Limit?
The Chandrasekhar Limit is the maximum mass of a stable white dwarf
What is the accepted figure for the Chandrasekhar limit?
The maximum limit is a Sun with a core 1.4 times the mass of the Sun
How is a Red Giant formed?
When the generation of energy stops, the radiation pressure becomes zero and the star gravitationally collapses. This raises the temperature of the star and causes the fusion of hydrogen again but this time in a shell around the core. The helium core further contracts which increases the rate of energy generated. This makes the star expand and form a Red Giant
What happens if a Red Giant’s core becomes extremely hot?
If the core become’s hot enough, helium will fuse into carbon
What are Planetary Nebula?
A planetary nebula is a nebula that is formed by an expanding shell of gas from an ageing star
Why does the core of a star eventually stop collapsing?
Electron Degeneracy Pressure
What is Electron Degeneracy Pressure?
Electron Degeneracy Pressure is because the electrons cannot be squeezed together any closer and so resist any further compression
What is formed after the Red Giant?
A White Dwarf
What occurs after a White Dwarf?
A Black Dwarf
Why do Black dwarfs form?
Black Dwarfs form after a white dwarf cools down and loses its energy
What happens if a star has a core mass greater than the Chandrasekhar limit?
If a star has a core mass greater than the Chandrasekhar limit, the star will continue to collapse and will be able to fuse carbon into Neon. Fusion continues until iron is formed in the core
What will happen if the core’s mass is greater than the Chandrasekhar limit but has a core mass less than 3x the mass of the Sun?
The collapse is stopped by the neutron degeneracy pressure
What is the neutron degeneracy pressure?
The electrons are forced into protons to form a solid core of neutrons, and these neutrons prevent being compressed further
