Life cycle of stars Flashcards
(27 cards)
What path does a sun- like star take on a HR diagram?
Starts as a protostar on the far right with absolute mag around five.
Moves left to become a main sequence star.
Moves up and right into the red giant territory.
Then moves to be a white dwarf.
What is a nebula and how does this progress in stellar evolution?
Nubulae are clouds of gas and dust that gradually clump together due to gravity. They begin to spin inwards to conserve angular momentum until they form a dense centre - a protostar.
What is a protostar and how does this progress in stellar evolution?
A protostar is a dense dust cloud in which fusion has not begun (it would then become a main sequence star). In a protostar, gravity pulls mass together, increasing the temp until the conditions are correct for fusion to begin to occur. It then produces a strong stellar wind to blow other material away.
What is fusion in a star?
Fusion begins with He and H atoms fusing together, making heavier elements. These new elements then fuse together in even hotter and denser conditions to form more elements.
What is the cycle of pulsing of a star caused ny?
Rate of fusion decreases ->
core temp decreases as less energy is being emitted ->
the gas shrinks (ideal gas) ->
temp increases ->
rate of fusion increases ->
core expands ->
temp decreases ->
rate of fusion decreases…
How does fusion keep a star stable?
The outward radiation emitted opposes gravity so that it does not collapse in on itself.
What is a main sequence star and how does it progress in stellar evolution?
The inward force of gravity and the outward force due to fusion are in equilibrium – the star is stable. Hydrogen nuclei are fused into helium.
Once the hydrogen begins to run out, the gravity is higher than the outward radiation and the star begins to heat up as it shrinks. This means the remaining H in the core burns faster.
How does the mass of a star dictate its lifespan?
The greater the mass of the star, the shorter its main sequence period because it uses its fuel more quickly.
What is a red giant and how does it progress in stellar evolution?
In a star with mass <1.4 mass of sun, when the last of the hydrogen is fused, the outer layers are pushed away and the temp of the core increases to such that heavier nuclei can fuse. Once all of these heavier nuclei have been used up, fusion stops and the core contracts into a white dwarf.
What is a white dwarf and how does it progress in stellar evolution?
When the core of a white dwarf is contracting, int throws off its outer layers, forming a planetary nebula around the dwarf. This star slowly cools until it is cold enough to be considered a black dwarf.
What is a red supergiant and how does it progress in stellar evolution?
Formed when a high mass star, >3 solar mass, runs out of hydrogen nuclei. The core collapses and heavier elements begin to fuse. Elements up to iron fuse.
What is electron degeneracy?
Mass that is made up of atoms containing electrons has a force that opposes compression past energy level n=1.
What stellar objects does electron degeneracy prevent the collapse of?
Reg giants and supergiants
Why are the lifespan of red giants and supergiants different?
Red giants are much more massive so burn their fuel much quicker.
What occurs when a red supergiant collapses or a star of mass >1.4 solar mass collapses?
When all fuel runs out , fusion stops and the core collapses inwards very suddenly and becomes rigid (as the matter can no longer be forced any closer together). The outer layers of the star fall inwards and rebound off of the core, launching them out into space in a shockwave. As the shockwave passes through surrounding material, elements heavier than iron are fused and flung out into space. The remaining core depends on the mass of the star.
What is released when a supernova occurs?
A gamma ray burst with about 10^44 J of energy.
What happens to a star of mass 1.4 SM < mass < 3SM after it has gone supernova?
When the core of a large star collapses, gravity is so strong that it forces protons and electrons together to form neutrons. A neutron star is incredibly dense – about 10 17 kg m - 3 (the density of nuclear matter ).
What prevents neutron stars from collapsing further?
Neutron degeneracy pressure.
What is a pulsar?
Spinning neutron stars that emit beams of radiation from the magnetic poles as they spin (up to 600 times per second)
What happens to a star of mass >3SM after it has gone supernova?
When the core of a giant star collapses , the neutrons are unable to withstand gravity forcing them together. The gravitational pull of a black hole is so strong that not even light can escape.
What is the event horizon of a black hole?
The point at which escape velocity = speed of light
What is a type 1 supernova?
When a star accumulates matter from its companion star in a binary system and explodes after reaching a critical mass
What is a type 2 supernova?
The death of a high mass star after it runs out of fuel.
What is a type 1a supernova?
A Type I supernova with a white dwarf . When the companion star in the binary system runs out of hydrogen, it expands, allowing the white dwarf to begin accumulating some of its mass. When the white dwarf star reaches a critical mass , fusion begins and becomes unstoppable as the mass continues to increase, eventually causing the white dwarf to explode in a supernova.
