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Stellar EvolutionStellar Evolution
What happens to the big What happens to the big stars?stars?
ContentsContents
White DwarfsWhite Dwarfs
Red Giants and SupergiantsRed Giants and Supergiants
SupernovaSupernova
Neutron starsNeutron stars
PulsarsPulsars
Black HolesBlack Holes
Life after DeathLife after Death
What makes a white dwarf?What makes a white dwarf?
Formation of Red GiantFormation of Red Giant
When a star stops burning HWhen a star stops burning H22 and He, the core and He, the core
will contract further by gravitywill contract further by gravity
Temp reaches 100 million K in the coreTemp reaches 100 million K in the core
He starts burning to CHe starts burning to C
During process, the star expands, then contracts During process, the star expands, then contracts a littlea little
He -> C fusionHe -> C fusion
A Red A Red GiantGiant
Formation of supergiantFormation of supergiant
After C, star expands again, while core contracts After C, star expands again, while core contracts further!further!
Stars not big enough -> supernovaStars not big enough -> supernova
Stars of enough mass -> core contracts to 600 Stars of enough mass -> core contracts to 600 million K!million K!
C starts burning to still heavier elements: OC starts burning to still heavier elements: O22, Ne, , Ne,
Mg, Si, Fe!!!Mg, Si, Fe!!!
Cross-section of a supergiantCross-section of a supergiant
Supernova: When?Supernova: When?When stars finish burning and do not have the mass to When stars finish burning and do not have the mass to continue another stage, it reaches supernovacontinue another stage, it reaches supernova
If the star finishes burning to Fe, it cannot burn Fe If the star finishes burning to Fe, it cannot burn Fe anymore!anymore!– Burning Fe does not produce heat but instead take in heat!Burning Fe does not produce heat but instead take in heat!
Burning Fe will cause heat to be absorbed from the Burning Fe will cause heat to be absorbed from the surrounding of the coresurrounding of the core
Implosion occurs..Implosion occurs..
Neutrinos form, blasts out -> supernovaNeutrinos form, blasts out -> supernova
SupernovaSupernova
During a supernova, the light seen from it is comparable to billions of stars at once!
H-RH-RDiagramDiagram
Evolution Evolution of of
high-mass high-mass starsstars
H-R Diagram of stellar evolutionH-R Diagram of stellar evolution
http://www.astro.ubc.ca/~scharein/a311/Sihttp://www.astro.ubc.ca/~scharein/a311/Sim/hr/HRdiagram.htmlm/hr/HRdiagram.html
Neutron StarsNeutron Stars
Neutron StarsNeutron Stars
Q: Why neutron? Why not proton or electron?Q: Why neutron? Why not proton or electron?
• In an atom:
• 99.9% of mass is in nucleus
• 0.1% electrons in orbit
• However:
• electron cloud takes 99% of the space in atom!
Neutron StarsNeutron StarsIn an implosion resulting in neutron star, gravity compresses the atom so much that the electron now binds with the proton in the nucleus.
The formula given is:p + e- -> n + neutrino
A neutrino is a very small particle and is ejected out of the core. It is what causes the supernova. What are left are neutrons. Thus they are named ‘neutron stars’
Neutron Stars ~Cool Facts~Neutron Stars ~Cool Facts~
They rotate up to 1000 rotations/secondThey rotate up to 1000 rotations/second
1,000,000 Kelvin at the surface1,000,000 Kelvin at the surface– compared to 5800 Kelvin for the Suncompared to 5800 Kelvin for the Sun
The gravitational acceleration is 100 billion g's! The gravitational acceleration is 100 billion g's! The escape speed at the surface of a neutron The escape speed at the surface of a neutron star is half the speed of light (150,000 km/sec vs star is half the speed of light (150,000 km/sec vs 11 km/sec for the Earth!)11 km/sec for the Earth!)
PulsarsPulsars
Pulsars are actually very rapidly spinning Pulsars are actually very rapidly spinning neutron stars giving out radio waves as neutron stars giving out radio waves as they spinthey spin
The ‘on’ and ‘off’ states of a pulsar that The ‘on’ and ‘off’ states of a pulsar that give the radio “wave” is due to the rotation give the radio “wave” is due to the rotation of the neutron star in misalignment with its of the neutron star in misalignment with its axis of rotationaxis of rotation
Pulsar in Crab NebulaPulsar in Crab Nebula
Crab NebulaCrab Nebula
Black HolesBlack Holes
Q: Q:
What is the What is the Chandrasekhar Chandrasekhar
limit?limit?
Black HolesBlack Holes
For stars of mass beyond the For stars of mass beyond the Chandrasekhar limit, even the neutron star Chandrasekhar limit, even the neutron star cannot hold backcannot hold back
The star collapses further inThe star collapses further in
As gravity is too strong for the star, it will As gravity is too strong for the star, it will continue collapsing until it reaches a continue collapsing until it reaches a singularitysingularity
Black HolesBlack Holes
An event horizon forms around the singularityAn event horizon forms around the singularity
In the singularity:In the singularity:– Density = ∞Density = ∞– Volume = 0Volume = 0
Why? Mass remains same as starWhy? Mass remains same as star– Density = Mass / VolumeDensity = Mass / Volume– In a singularity, volume cannot be measured, In a singularity, volume cannot be measured,
therefore = 0therefore = 0– Thus density = ∞ (division by zero)Thus density = ∞ (division by zero)
Types of Black HolesTypes of Black Holes
Stellar: Normal in sizeStellar: Normal in size
Mid-massive: 100+/- solar massMid-massive: 100+/- solar mass
1000+ solar mass!1000+ solar mass!– Usually found in the middle of galaxies (with a Usually found in the middle of galaxies (with a
lot of interstellar matter)lot of interstellar matter)
Primordial?Primordial?
List of known black holesList of known black holes
Cygnus X-1 Cygnus X-1
Circinus X-1 Circinus X-1
V404 in Cygni V404 in Cygni
V861 Sco in Scorpius V861 Sco in Scorpius
LMC X-3 in the Large Magellanic CloudLMC X-3 in the Large Magellanic Cloud
Warning: List is not exhaustive!
Space-Time Fabric WarpSpace-Time Fabric Warp
How to detect black holesHow to detect black holes
Wanna see a black hole?Wanna see a black hole?
Green crosshair shows black hole in M82
Saggitarius A*Saggitarius A*
Circling a black holeCircling a black hole
Approaching a black holeApproaching a black hole
Stellar Evolution of big-mass starsStellar Evolution of big-mass stars
““The bigger you are, the smaller you finally go”The bigger you are, the smaller you finally go”
- Yours truly
Black Hole> 3
Neutron Star1.4 – 3
White Dwarf< 1.4
End ProductSize of star (n solar masses)
Wormholes?Wormholes?
Possibility of wormholes in a black holePossibility of wormholes in a black hole
Why?Why?– Space-time curved to infinity -> we do not Space-time curved to infinity -> we do not
know what is happening!know what is happening!
Life after DeathLife after Death
Can stars come back to life after dying?Can stars come back to life after dying?
Life after DeathLife after Death
Accretion: ‘sucking’ of mass from nearby starsAccretion: ‘sucking’ of mass from nearby stars
When a white dwarf gains enough mass, it When a white dwarf gains enough mass, it contracts and starts nuclear fusion all over contracts and starts nuclear fusion all over again!again!
However, the fusion quickly endsHowever, the fusion quickly ends– Nova (smaller in scale than supernova)Nova (smaller in scale than supernova)
For some binaries, novae are periodicalFor some binaries, novae are periodical
Stellar Evolution ~A summary~Stellar Evolution ~A summary~
Thanks! To:Thanks! To:
http://www.eclipse.nethttp://www.eclipse.net
http://chandra.harvard.eduhttp://chandra.harvard.edu
http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.htmlhtml
(virtual trips to black holes and neutron (virtual trips to black holes and neutron stars)stars)