The Life History of Stars – High MassOutline

•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

MommyFetusAdultOld Man

Heart AttackCorpse

Supergiant Stages•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

Variety of fuels burned in massive stars:•Main Sequence: Hydrogen Helium•CHB/DSB: Helium Carbon/Oxygen•More stages:•Carbon Neon•Neon Silicon, Oxygen•Oxygen Silicon•Silicon Iron

•Each stage produces less energy than the last•Each stage goes faster than the last

Supergiant Stages

HydrogenHeliumCarbon/OxygenNeonSiliconIron

•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

Supergiant Stages

Stages Go Steadily Faster – 25 MSun star

•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

Stage Fuel TimeMain Sequence Hydrogen 7 MyrCHB/DSB Helium 700 kyr

Carbon 600 yrNeon 1 yrOxygen 6 monthsSilicon 1 day

(Collapse) Iron (?) 1 second

Late Stages

•Iron can’t burn – it is completely “burned”•When it hits the Chandrasekhar limit, it will collapse under its own weight

Supergiant S

tages

Core Collapse•Iron Core begins to collapse•Iron disintegrates•P n5/3/m

•Electron degeneracy pressure enormous•Will do anything to get rid of electrons

•Electron + proton neutron + neutrino

•Electrons (and protons) disappear•Pure neutrons

+ +

•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

How come the neutron’s degeneracy pressure doesn’t support the core from collapse?A) Neutrons don’t have itB) Neutron is much more massiveC) Neutrons are neutral – no electric repulsion

Core Bounce

P n5/3/m•Eventually, the neutron’sdegeneracy pressure kicks in

•Core slams to a stop in 1millisecond•Rings like a bell

•Temperature soars 1 trillion K•Over next 10 seconds, energypours out in the form of(invisible) neutrinos

•More than rest of Universe!•Shock wave expands outwards and destroys star

Iron Core

Protons, Neutrons, Electrons

Core Bounce

Shock Waves

Neutron Star

Massive Star Supernova•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

Massive Star Supernova

HydrogenHeliumCarbon/OxygenNeonSiliconIron

•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

Supergiant Stages

•Expanding shock wave slams through the rest of the star

•Takes several hours•Every other element is produced

•Most of the mass of the star – including many heavy elements – get recycled back into the Universe – a Supernova Remnant

•The Earth is made of star stuff•The ball of neutrons – a neutron star – remains at the center

After the Supernova•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

Supernovae

SN1994 D

Supernova 1987a

SN1987A

Supernova Remnant – Crab Nebula

Supernova Remnant – Crab Nebula

Near Ultraviolet Far Ultraviolet

VisibleX-Rays

Supernova Remnant – Crab Nebula

X-RaysX-Rays Plus Infrared

Tycho’s Supernova Remnant

Puppis AVeil Nebula

Supernova Remnants

W49B

N49

Kepler SNR

Supernova Remnants

Tarantula Nebula

Supernova Remnants

Supernova Remnants – Vela Nebula

Supernova Remnants – DEM L316

0

5

10

15

20

Neutron stars•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

•Structure•Pure neutrons•Held up by neutron degeneracy pressure

•Mass•Most around 1.4 MSun

•Maximum mass2 – 3 MSun

•Size•Typically 25 km •More massive smaller

Neutron stars•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

Pulsars•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

•Most stars spin•Shrinking core spins faster

•Magnetic fields, trapped, get concentrated•Whirling strong magnet

•Charged particles get whipped around by magnet - they radiate

•Lighthouse effect

PulsarsCrab Pulsar Optical and X-ray

Forming a Black Hole•Molecular Cloud•Protostar•Main Sequence•Supergiant Stages•Massive Star Supernova•Neutron Star or Black Hole

Very massive stars (>30 MSun)•Core gets too heavy and collapses toneutron star•Outer layers not completely blownaway – they fall back towards the star•Mass exceeds maximum mass•Gravity exceeds pressure•Star collapses again

•Once it reaches its event horizon, nothing can stop it•It becomes a black hole

•Infinite density

Einstein’s Theories of Relativity•Special Theory of Relativity

•Says nothing can go faster than light•General Theory of Relativity

•Describes gravity•Using Newton: Escape velocity:

•You can’t escape when ve = c•You can’t escape if you are closer than:

•The event horizon

2 2e

GMv

R

2

2e

GMR

c

2

2

e

GMR

v

3 kme

MR

M

Event Horizon

SingularityHelp!

Gamma Ray Bursters•There are intense bursts of gamma rays

•Typically last about 30 seconds•Brighter than a supernova

•Followed by “fireball” of visible light•Followed by a massive star supernova explosion•Cause is probably very massive star death and creation of black hole

•They occur in galaxies•Typically, galaxies have lots of young stars in them