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)