Stellar Evolution Flashcards
Detail the death of sun- like stars. 6 stages.
- Star on main sequence gets slowly brighter over about a 10 billon year period.
- When hydrogen is all used up in the core it begins burning hydrogen in a shell around it. Star then swells and becomes brighter as a Red Giant
- Helium Flash = core gets hot enough to fuse helium = star contracts no longer a red giant = Carbon and oxygen fused.
- Final (Asymptotic) Giant Phase = helium + hydrogen burning in shells
- Planetary Nebula = outer layers thrown off as fusion ceases
- White Dwarf = core of the star is the size of Earth = takes billions of years to cool = degenerate carbon
How does nuclear fusion work?
The core of stars is filled with Hydrogen. Two hydrogen protons then fuse. One proton becomes a neutron by shooting of a positive and a electron neutrino (things that give protons a positive charge). The Deutrium then fuse with another proton. Two of these Deutriums then fuse to form a nuclei fuse. An alpha particle is then formed with the energetic release of 2 protons.
How do Type 1a Supernovas form?
- Two normal stars are in binary pair.
- The more massive star becomes a giant…
- Which spills gas onto the secondary star, causing it to expand and become engulfed.
- Now inside the giant, the secondary lighter star and the core of the giant spiral towards one another
- The common envelope (planetary nebula) is ejected while the separation between the core and the secondary star decreases.
- The remaining core of the giant collapses and becomes a white dwarf.
- The aging secondary star starts swelling, spilling gas onto the white dwarf.
- The white dwarf star’s mass increases until it reaches critical mass and explodes…
- Causing the secondary star to ejected away.
What elements can be found in a Type 2 Supernovas core?
Hydrogen, Helium, Carbon, Oxygen, Neon, Magnesium, Silicon, Iron
What element cause a star to explode and why?
Iron because it absorbs the energy instead of using to continue fusing other elements. When the fusion stops, gravity overcomes the pressure.
What are the 6 stages of the collapse of the iron core?
- The onion layered shells of elements begin fusing a nickel-iron core.
- It reaches the Chandrasekhar mass and starts to collapse. The inner part of the core is compressed into neutrons.
- This cause the infalling material to bounce
- Forming an outward propagating shock force. The shock starts to stall
- But is reinvigorated by the neutrino interaction. The surrounding material is blasted away.
- This leaves a degenerate material.
Draw the lighthouse model of pulsar stars.
Include: Rotation Axis Magnetic field Radiation beam of light Star Rotation path
What happens to the speed of pulsars over their life?
During their life pulsars slow down.
What creates the beam of light?
The magnetic fields.
How did Einstein define gravity?
A distortion or warping of space and time caused by mass.
What did Schwartzchild solve?
Einstein’s equations and showed that an object could exist with an escape velocity greater than the speed of light. This means that nothing including light that enters a blackhole will ever leave it.
What is the Schwarzchild radius?
The radius of an object with an escape velocity of c= speed of light.
Equation: R= 3km X Mass/Sun’s mass
What are the 2 main types of black holes?
Stellar and Supermassive
Describe Stellar Black Holes:
Formed in Supernova explosion (Core of star)
Larger than 3 solar masses.
Remaining material can be forced out in a gamma ray burst
Gives off X rays when material from companion stars are ripped off and forced into the hole.
What are the 4 stages of the birth of stars?
- Molecular cloud of about 75% hydrogen, 25% helium
- More dense regions clump together under their own gravity
- Central region becomes spherical + Begins to rotate + Speeds up
- Pressure rises + Heats up + Fusion ignites + Star Born
Describe Supermassive Blackholes.
Usually found in the centre of galaxies.
Are called Quasars when they are growing. The material being devoured is so great they give off light similar to pulsars.
Explain the journey into a blackhole.
10X the size of our sun and you are going in feet first.
The Schwartzchild radius is 30km which is known as the event horizon.
At 1500km you feel a slight pull of your feet. Only the 1/8th of the earths gravity. Similar to tidal forces.
8000km the pull is 4 times as strong as Earth’s gravity.
3000km the gravity is 15 times the Earth’s. As you get closer, spaghettification make you longer and thinner. Slowly ripper into a stream of particles.
Possibility of a singularity at the centre where space and time are infinitely distorted.
Observer would see you fall in slower and slower and redder and dimmer. Time slows down.
How do blackholes die?
Hawking radiation. Which are quantum particles which can leave the black hole. If the blackhole gets hotter than the universe (as the universe cools down due to lost mass) then Hawking radiation occurs. Once it begins it cannot stop. The radiation speeds up until it gets hotter and then eventually blows up.
Anatomy of a Black hole
Photonsphere= light trapped in orbit around the blackhole. 1.5 times the Schwartzchild Radius.
Event horzion= Schwartzchild Radius.
Singularity = middle
How big does a protostar have to be to become a brown dwarf?
Less than 0.1 solar masses
How big does a protostar have to be to become a Main Sequence Star?
Larger than 0.1 solar masses
How big must a mainsequence be to become a Super Giant
Larger than 2 solar masses
What happens to all stars smaller than 6 solar masses after the red/super giant phases?
Planetary nebula - White Dwarf
How large must a star be to become a supernova?
Larger than 6 solar masses
How big must a supernova be to become a blackhole?
Larger than 3 solar masses
How big must a supernova be to become a neutron star?
Smaller than 3 solar masses
What can neutron stars become?
Pulsars
Describe white dwarves.
Made up of degenerate gas which exert pressure as all the energy levels are full.
The more mass, the smaller the radius. Opposite to how usual mass behaves.
Only as big a 1.4 solar masses due to the Chadrosekhar Limit
No energy released
Core of a dead star
Describe Neutron Stars
Atoms got destroyed as the star collapsed leaving only neutrons behind which exert pressure. Rapidly spinning Huge magnetic field Formed in supernova explosion Heavier than 1.4 solar masses Compact and dense Spins 600 times a second Spoonful of white dwarf =elephant Spoonful of neutron star = billion elephants
What is the balance stars have to maintain?
Gravity puling in and energy pushing out
What happens when gravity wins?
When energy is no longer produced gravity wins and the centre of the star is crushed. Outer layers push outwards though to form Red Giant.
What happens when a white dwarf steals material from its companion?
Heavier + Denser = less stable
Carbon and Oxygen fuse into which element?
Iron
Where does most of the iron in the universe come from?
Type 1a Supernovas
How are elements heavier than iron made?
Big stars exploding in a single star explosion.
What are 2 facts about massive stars?
Burns faster
Quicker reactions
Lots of elements fused before explosion
What does Iron do to energy?
Eats up all the energy. Absorbs it all
What happens to the core of the star once gravity begins to crush it?
The core collapse further crushing the atoms together. The denser it becomes the more energy it creates.
What do fast spinning neutron stars create?
Pulsars that send jets of energy out of their poles.
What do massive supernovas make?
100 solar masses
Hypernova
Blackhole
What causes gamma ray bursts?
Collapse of a stars core into a blackhole which forms accretion disks.
Black hole can’t cope with all the material being pushed into it so it shoots to beams of energy out of black hole.
Gamma rays travel at the speed of light.
What powers a black hole?
Gravity
Why are black holes black?
Light can’t even escape it.
What would a blackhole do to our solar system?
- disrupt balance of solar system
- tear planets from their orbits
- crush things
- cause collisions
- steal moons
What happens when a black hole forms?
Eats all the gas inside the star
Blasts out huge jets of energy
Destroys corpse of star
What is the problem with black holes and the laws of physics?
Time stops
Gravity becomes infinite
Explain spaghettificaction.
Stretched out as the gravity is stronger at your feet then at your head.
Smaller the black hole the greater the distance
Can the singularity grow?
Yes
How could they tell there was a super massive blackhole at the centre of the galaxy?
Densely packed stars
Stars move extremely quickly around the centre
4 million solar masses
Throwing stars around their orbits.
What could theoretically be possible due to blackholes?
Space travel
Time travel
Parallel univere
Describe the Chandeshakhar limit?
If the core of a star exceeds the Limit of 1.44 solar masses than it will explode in a Type 2 supernova. If not then the star becomes a white dwarf
If a white dwarf gains enough mass to exceed the Limit than it will explode in a Type 1a supernova.
