What are stars formed out of
The interstellar medium
-new stars formed in dense dust and gas clouds
-gravity collapses dust and gas with an angular momentum which becomes a protostar
When protostar becomes hot enough it fused hydrogen atoms
-after millions of years a bipolar flow erupts from protostar and blasts away dust
How is energy produced in stars
Through nuclear fusion
E= mc^2
Proton-proton chain (p-p chain)
Energy fusion reactions
- difference of mass that disappears from 4H to 1H is called mass defect
- the binding energy is the same energy needed to break the nucleus apart
Solar Neutrino problem
- could only detect 1/3 of neutrinos we should
- SNOW lab looked for all three neutrinos and found all of them
- they start as Ve but can change to any Vc or Vu
Hydrostatic equilibrium
Keeps stars in balance whilst they have efficient fusion
- pressure balances gravity
- most stars spend most of their lives in this state
Most important property of stars
Stellar mass
-governs lifetime, colour, sizes
Herzsprung-Russell (colour-magnitude)
- plots stars based on luminosity and temperature(colour)
- main sequence: where most stars on graph due to hydro equilibrium
Post main sequence evolution
- formation of red giant
- hydrogen in core runs out
- moves out of hydro equilibrium
- gravity compresses and core heats up
- core gets hotter but she’ll becomes cooler and expands
- starts burning He in the core and H in the shell
- stars higher on the main sequence burn faster
- low mass stars have better convection and low burning so they live longer
Elements in stars
- stars start with He and H from which all elements were made from
- near the core elements are placed around like an onion
- these elements are created through nucleosythesis
Brown dwarfs
- are failed stars that do not have enough mass
- need a min mass of 0.08M
- they can’t fuse H but can fuse deuterium
Death of sun like stars
1-8M
- create a planetary nebula
- surface of red giants become unstable due to weak gravity
- surface temp becomes so low the solid gas forms in atmosphere
- core reactions become unstable
- lose the outer shells of the star and all that’s left if the core (carbon/oxygen)
- geometry of nebula based on rotation of magnetic field
White dwarfs and degenerate matter
- stars get very bright and hot for a long time but then they cool down
- becomes a white dwarf which is the end point for stars
- carbon oxygen core
- they have a lot of mass but no temp source so they become degenerate
- the core is being squished with nothing to counter it
Pauli exclusion principal
In each energy level only allowed to have two particles with spin up and down
-energy levels are full and locked in place and can not regulate itself
The Chandrasekhar limit
As you increase the mass the size gets smaller l
- ends up in a run away reaction
- 1.4 Mo certain mass threshold, where the whole object would collapse
Properties of white dwarfs
- a white dwarf in isolation will not grow mass
- In a WD system it overspills the L1 legrangian point where gravities are equal
- the Roche lobe is what gravity dominates
- WDs fill their Roche lobes which causes mass from other star to funnel onto the WD
- this new mass can cause reactions on the surface and it will become unstable and explode in a supernova
Supernova
- SNI: no H in its spectrum
- SNII: does have H in spectrum (neutron star)
- Io: specific supernova for white dwarfs in binary system
-SNIa: WD crested from RG (no remnant)
Death of most massive stars
8-10Mo
- have high temps for reactions
- mass lost in conversions converted to energy
- energy is released in fission
- create energy by splitting massive elements or fusing light elements
- stars can not create iron in its core so this is the end of the line
- stars collapse due to gravity
- this sends and shock wave and rips away surface of the star
- this is a type 2 supernova
Neutron stars
- held up by the degenerate pressure of neutrons
- electrons and protons pushed together it create neutrons
- size of a city
- shrinking into a neutron star increases velocity
- have a magnetic remnant
Jocelyn Bell
- found periodic radio pulses
- pulsars are rotating neutron stars where we see pulses of the rotation
- no pressure that can hold matter after neutron degenerates
Black holes (stellar mass)
- nothing can hold up its mass
- it collapses and has infinite mass
- if the remnants mass exceeds limit for neutron degeneries, becomes a black hole
- find the stellar mass of black holes through the transfer of material from a star into a black hole
- this makes the accretion disk
Schwarzschild radius
- radius of the even horizon
- from the point of singularity to even horizon
Einstein’s theory of relativity
- Theory of special relativity: motion near the speed of light
- Theory if general relativity: gravity near large masses
Special relativity
The faster an object moves
- The heavier it becomes
- The slower time travels
- The shorter things become
General relativity
- equivalence principle: acceleration can be due to being close to a mass and acceleration due to motion. Can’t distinguish between the two
- mass tells space time how to curve and the curvature tells mass how to move and accelerate
