JimH This is Your Life

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This Is Your Life
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But first, a little background
Kirchhoff's Laws
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Kirchhoff's laws ,there are three types of
spectra continuum, emission line, and absorption
line.
High pressure, high temperature gas
Low pressure, high temperature gas
Cool gas in front of continuous spectra source
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Continuum
Absorption Lines
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Doppler effect

• similar in light and sound

• Waves compressed with source moving toward you
  Sound pitch is higher, light wavelength is
  compressed (bluer)

• Waves stretched with source moving away from you
• Sound pitch is lower, light wavelength is longer
  (redder)

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Red Shift
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Inverse square of light
If two stars are similar and one star is 3 times
as far away, as the other, its intensity will
be 1/9.
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Spectra of Stars
OBAFGKM
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Stars are different colors, because they are
different temperatures
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Spectral Classification

• Annie Cannon classified stars according to the
  strength of the hydrogen absorption lines in the
  sequence A, B, C.P

• These spectral classes were changed to a
  temperature-ordered sequence and some were
  discarded, finally leaving

Subclasses
O B A F G
K M
35,000 K
3,000 K

• Oh, Be A Fine Girl (Guy) Kiss Me

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The Spectral Sequence
Spectral Sequence is a Temperature Sequence
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O Stars
Hottest Stars Tgt30,000 K Strong He lines no H
lines
T 11,000 - 30,000 K Strong He lines very weak
H lines
B Stars
T 7500 - 11,000 K Strongest H lines, Weak Ca
lines.
A Stars
T 5900 - 7500 K H grows weaker Ca grows
stronger, weak metals begin to emerge.
F Stars
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T 5200 - 5900 K Strong Ca, Fe and other
metals dominate,
G Stars
T 3900 - 5200 K Strong metal lines, molecular
bands begin to appear
K Stars
T 2500 - 3900 K strong molecular absorption
bands particularly of TiO
M Stars
Solar Spectrum
4000 A

7000 A
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Spectra Part II
Quantum Mechanics
Electrons can only orbit the nucleus in certain
orbits.

• n 1 First orbital Ground State)
• Lowest energy orbit .

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Down emission
Hydrogen Spectrum
Up absorption

• Hydrogen (1H) consists of
• A single proton in the nucleus.
• A single electron orbiting the nucleus.

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Emission Lines Balmer Lines When an electron
jumps from a higher to a lower energy orbital, a
single photon is emitted with exactly the energy
difference between orbitals. No more, no less.
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Absorption Lines Balmer Lines An electron
absorbs a photon with exactly the energy needed
to jump from a lower to a higher orbital. No
more, no less.
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Hydrogen lines absent in the hottest stars
because, photons ionize electrons.
They are also absent in the coolest stars
because, photons dont have enough energy to move
the electrons from n2 to higher energy levels.
No electrons, no lines.
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HR Diagram
In 1905, Danish astronomer Hertzsprung, and
American astronomer Russell, noticed that the
luminosity of stars decreased from spectral type
O to M.
To bring some order to the study of stars, they
organize them in the HR diagram.
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HR Diagram
Supergiants
Giants
Main Sequence
White Dwarfs
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As you move up the H-R diagram on the Main
Sequence from M to O, the stars get hotter and
larger
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Back to this is your life
Star
Formation
All we are is dust in the wind - Kansas
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(GMC) in Orion
Protostars form in cold, Giant Molecular Clouds

• About 1000 GMCs are known in our galaxy
• These clouds lie in the spiral arms of the galaxy

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The Cone Nebula
Examining a Star Forming Region
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Giant Molecular Clouds (GMC)
are mostly composed of molecular hydrogen.

• Properties
• Radius 50 pc (160 ly)
• Mass 105 Msun
• Temperature 10-30 K

• Also, small amounts of He,and others

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Size of cloud large, Compression area - small
GMCs resist forming stars because of internal
pressure (kinetic energy) so, a cooler gas is
needed.

• A shockwave is needed to trigger formation, and
  to compress the material .

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Sources of Shockwaves 1.Supernova explosions
Massive stars die young .
2. Previous star formation can trigger more
formations

3. Spiral arms in galaxies like our Milky Way
Spirals arms are probably rotating shock waves.
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An expanding supernova explosion , occurring
about 15,000 years ago.
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Gravity Contraction
As the cloud is compressed, cool blobs contract
into individual stars.
The blobs glow faintly in radio or microwave
light.
As they heat up, blobs glow in the infrared,
but they remain hidden .
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As protostar compresses Density increases
Temperature rises. Photospheres
(3000K) Rotation increases as it shrinks in size.
What types of stars form ? OB - Few AFG - More KM
- Many, Many
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Many of the cooler stars, spectral classes G,K,M,
become heavy gas-ejecting stars called T-Tauri
stars. Stars blows away their cocoon
Leave behind a T Tauri star with an accretion
disk and a jet of hot gas.
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A T-Tauri star can lose up to 50 of its mass
before settling down as a main sequence star.

False Color Green scattered starlight and red
emission from hot gas.
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Motion of Herbig-Haro 34 in Orion

• You can actually see the knots, called
  Herbig-Haro objects, in the jet move with time

• They can have wind velocities of 200-300 km/s.
  This phase lasts about 10 million years.

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Low-Mass Protostars

• Collapse is slower for lower masses
• 1 Msun (solar Mass) 30 Myr
• 0.2 Msun 1 Billion years

• When core temperature 10 Million K
• Core ignites, P-P chain fusion begins
• Settles slowly onto the Main Sequence
• Has a rotating disk, from which planets
• might form .

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• Actual Protoplanetary Disks

• The disks are 99 gas and 1 dust.
• The dust shows as a dark silhouette against the
  glowing gas of the nebula.

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High-Mass Protostars Collapse is very rapid 30
solar mass protostar collapses in 30,000 years
When core Temperature gt10 Million K Ignite
first P-P Chain then CNO fusion in the core.
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Clouds are blown away from the new stars
near the stars
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Protostars!
The Cocoons of proto-stars are exposed when the
surrounding gas is blown away by winds and
radiation from nearby massive stars.
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• The Main Sequence
• Core temperature pressure rise
• Collapse begins to slow down

• Finally
• PressureGravity collapse stops.
• Becomes a Zero-Age Main Sequence
• Star, (ZAMS).

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• Pre-main sequence evolutionary tracks

Most everything about a star's life depends on
its MASS.
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Meanwhile, back in the GMC, things are still
happening
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The original stars are growing, especially O B
stars.
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Stars Form in Clusters

Our own Sun is part of an open cluster that
includes Alpha Centauri and Barnard's star.
Gravitational interactions will cause some stars
to eventually leave over time
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Extreme Minimum Mass 0.08 Msun Below this
mass, the core never gets hot enough to ignite H
fusion. Star becomes a Brown Dwarf

• Resemble "Super Jupiters"
• Only about 100 are known
• Shine mostly in the infrared

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Extreme Maximum Mass 60-100 Msun

• The core of a very massive star gets so hot
• Radiation pressure overcomes gravity,
• star becomes unstable disrupts.
• Upper mass limit is not well known.
• Such stars are very rare.

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Star spends 90 of their life on the MS
Main
Sequence
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Stars on the Main Sequence, are in Hydrostatic
Equilibrium . Gravity pulling inward wants to
contract the star Pressure pushing outward wants
to make the star expand
The star neither expands nor contracts.
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Core-Envelope Structure Outer layers press down
on the inner layers. The deeper you go, the
greater the pressure.

• The star develops a
• hot, dense, compact central CORE
• surrounded by a cooler, less dense, ENVELOPE

                                                  
Core

• CORE

Envelope
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• Energy is transferred inside stars by
• Radiation (core)
• Energy is carried by photons from core.
• Photons hit atoms and get scattered.
• Slowly stagger to the surface
• Takes 1 Million years to reach the surface.
•                                     

Convection (Envelope) Energy carried from hotter
regions to cooler regions above by the motions
of the gas. Everyday examples of convection are
boiling water.
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Energy in a Main-Sequence star is generated by
fusion of H into He

• This process is performed in two ways
• 1. Proton-Proton (P-P) Chain (Low mass stars)
• 4 1H into 1 4He. energy.
• Efficient at low core Temperatures (TClt18M K)

• 2. CNO Cycle (High mass stars)
• Carbon acts as a catalyst
• Efficient at high core Temperatures(TCgt18MK)

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More massive stars have the shorter life time

• O B stars burn fuel like an airplane!

• M stars burn fuel like a compact car!

Every M dwarf ever created is still on the main
sequence!!
Main Sequence Lifetimes Main Sequence Lifetimes Main Sequence Lifetimes
Spectral Type Mass (Solar masses) Main sequence lifetime (million years)
O5 40 1
B0 16 10
A0 3.3 500
F0 1.7 2700 2.7 BY
G0 1.1 9000 9 BY
K0 0.8 14 000 14 BY
M0 0.4 200 000 200BY
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Death of Low Mass Star
Its the end of the world as we know it . REM
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The End-States for Low and High Mass Stars
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Evolution of Low-Mass Stars Main Sequence Phase
Energy Source H core fusion (P-P cycle) Slowly
builds up an inert He core

• Lifetime
• 10 Byr for a 1 Msun star( Sun)
• 10 Tyr for a 0.1 Msun star (red dwarf)

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When all H in core converted to He
He core collapses and heats up

• High temperatures ignites H burning in a shell

Outer layer expands and cools Star becomes a Red
Giant
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• Outside
•                                                   
                                        

• Envelope size of orbit of Venus

• The star gets brighter and redder, climbs up the
  Giant Branch. (Takes 1 Byr)

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• At the top of the Red Giant Branch
• Tcore reaches 100 Million K

He fusion begins in core Fusion of three 4He
nuclei into one 12C nucleus.
A secondary reaction forms Oxygen from Carbon
Helium
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Helium Flash in the core.
Short period of fast burning, then.
star contracts, gets a little dimmer, but hotter .
Moves onto the horizontal branch.

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Horizontal Branch Phase

• Structure
• He-burning core
• H-burning shell

Build up of a C-O core, still too cool to ignite
Carbon
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• After 100 Myr, core runs out of He.
• Inside
• C-O core collapses and heats up
• He burning shell outside the C-O core
• H burning shell outside the He shell
•                                      

Outside Star swells cools
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Climbs the Giant Branch again, slightly to the
left of the original Giant Branch .
                                                  
                                      
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Helium shell flash produces a new powerful
explosion, that pushes the outer envelope
outward. Core and Envelope separate.
With weight of envelope gone, core never reaches
600 million K, no Carbon fusion
Core contraction is stopped by electron
degeneracy.
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A Planetary Nebula forms                   
                                                  
               
Hot C-O core is exposed, moves to the left
Becomes a White Dwarf
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Expanding envelope forms a ring nebula around the
White Dwarf core.
Ring is Ionized and heated by the hot central
core of WD.
Called planetary nebula because look like a tiny
planet in a small telescope.

• The nebula expands at the 35,000 to 70,000
  miles/hour.

Expands away in 10,000 yrs
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Planetary Nebulae
Often asymmetric, possibly due to
Stellar rotation
Magnetic fields
The Butterfly Nebula
The Hour Glass Nebula
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White Dwarf Properties Radii 1000-5000 km (
size of Earth!)Temp. from 100,000 to 2500
K.So small, that they can only be seen if
close-by, or in a binary systems.
White Dwarfs mass lt than the Chandrasekhar mass
(1.4 Solar Masses).
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• White Dwarf Properties
• The core is tightly packed
• One teaspoon weighs about 5 tons.

Shine by leftover heat, no fusion. Fade slowly,
becoming a "Black Dwarf.

• Takes 10 Tyr to cool off , so none exists yet.

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The most famous W.D. is Sirius companion .
Sirius B Temp. 25,000 K Size 92 Earth's
diameter Mass 1.2 solar masses
The mass of a star, in the size of a planet.
Sirius B
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About half the stars in the sky are binaries.
What about Binary Stars with one being a W.D. !
But wait thats not all!
Mass could transfer from the star to the W.D.
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White Dwarf in a binary system..
White Dwarf
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Evolving (dying) star
Roche Lobes
II
Evolving (dying) star
White Dwarf
Accretion Disk
III
Evolving (dying) star
Roche Lobe filled
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A w.d. can take on material but , if the w.d.
exceeds 1.4 solar masses, powerful explosions
take place, and they can repeat.
Type 1a super NOVA!!
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Since the Type 1a supernova is always a white
dwarf they can be used to judge very great
distances (using the inverse square law).
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Stellar Graveyard High Mass Stars
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The End-States for Low and High Mass Stars
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Evolution of High Mass Stars Massive stars go
through about the same internal changes as low
mass stars, except

• massive stars evolve more rapidly due to greater
  gravity.
• massive stars can produce heavier elements

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• Evolution of High-Mass Stars
• O B Stars (M gt 8 Msun) (The James Dean of
  stars )
• Burn Hot
• Live Fast
• Die Young

• Main Sequence Phase
• Burn H to He in core using the CNO cycle
• Build up a He core, like low-mass stars
• But this lasts for only 10 Myr

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• After H core exhausted
• Inert He core contracts heats up
• H burning in a shell
• The Envelope expands and cools
• Envelope size of orbit of Jupiter
•                                            

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Moves horizontally across the H-R diagram,
becoming a Red Super giant star
                                                  
                                 
Takes about 1 Myr to cross the H-R diagram.
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Core Temperature reaches 170 Million K
Helium Flash Helium Ignites producing C O
Star becomes a Blue Supergiant.
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• He runs out in the core
• Inert C-O core collapses heats up
• H He burning shells expand
• Star becomes a Red Supergiant again
•                                                 
                                     

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• C-O Core collapses until
• Tcore gt 600 Million K
• Ignites Carbon Burning in the Core.

Carbon Burning 2- 12C fuse to form Mg, Ne and
O Carbon burning 1000 years
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Fusion now takes place rapidly Neon burning 10
years Oxygen burning 1 year Silicon burning
1 day
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Finally builds up an inert Iron core.
End of the road !
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Core of a massive star at the end of Silicon
Burning                                       
                                                  
           
Onion Skin
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Collapse is final Protons electrons form
neutrons neutrinos. .

• At the start of Iron Core collapse
• Radius 6000 km (radius of earth)
• Density 108 g/cc

• A second later!! , the properties are
• Radius 50 km
• Density 1014 g/cc
• Collapse Speed 0.25 c !

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Material falling inwards is stopped by neutron
degeneracy pressure .
This material rebounds, causing the outer
atmosphere, and shells, to be blown off in a
violent explosion called a supernova.
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Elements heavier than Lead are produced in the
explosion.
The supernova star will outshine all the other
stars in the galaxy combined.
The Famous Supernova SN 1987A
type II Supernova
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• The Crab Nebula.
• This nebula is the result of a supernova that,
  exploded in 1054.
• The supernova was brighter than Venus for weeks
  before fading from view.

• The nebula is expanding at more than 3 million
  miles per hour.

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• Structure of a Neutron Star
• Diameter- 10 km in diameter
• 3gt Mass gt 1.4 times that of our Sun.
• One teaspoonful would weigh a billion tons!
• Rotation Rate
• 1 to 100 rotations/sec

Inside a Neutron Star
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Pulsar Magnetic axis
is not aligned with the rotation axis.

• Lighthouse Model

Spinning magnetic

field generates a
a strong electric field.
We will see regular, sharp pulses of light
(optical, radio, X-ray) , if its pointed toward
the earth.
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The discovery of a pulsar in the crab nebula was
the key connecting pulsars and neutron stars.
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Black Holes
We know of no mechanism to halt the collapse of a
compact object with mass gt 3 Msun.
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The effect of gravity on light
Relativity implies nothing can go faster than
light. As you travel faster, time slows down, you
get more massive and your length appears to get
shorter.
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Singularities

• If the core of a star collapses with more than 3
  solar masses, electron degeneracy and neutron
  degeneracy cant stop the gravitational collapse.
• The star collapses to a radius of zero , with
  infinite density and gravitycalled a Singularity.

Position
Particle paths in a collapsing star
singularity
Event horizon
Time
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The Schwarzschild Black Hole The simplest of all
black holes. A static, non-rotating mass. The
Schwarzschild Radius defines the Event Horizon.
We have no way of finding out whats happening
inside the Event horizon
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The Kerr Rotating Black HoleThe singularity of a
Kerr Black Hole is in infinitely thin ring around
the center of the hole.
The event horizon is surrounded by the
ergosphere, where nothing can remain at rest.
Here spacetime is being pulled around the
rotating black hole.
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An object is moving fast enough, can enter the
ergosphere and fly out again. If the object
stops in the ergosphere, it must fall into the
Black Hole.
General Relativity predicts Wormholes for Kerr
Black Holes, but Astrophysicists are skeptical.
It may be possible to avoid the singularity.
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• Various Black Holes
• Primordial can be any size (created with Big
  Bang).
• Stellar mass black holes must be at least 3
  Mo many examples are known

• Intermediate black holes range from 100 to 1000
  Mo - located in normal galaxies many seen
• Massive black holes about 106 Mo such as in
  the center of the Milky Way many seen
• Supermassive black holes about 109-10
  Mo-located in Active Galactic Nuclei, have jets
  many seen

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•  Candidate For Black Hole
• Cygnus X-1 Binary Star w/ two objects
• M30 Msun primary ,
• M7 Msun companion
• Bright in X-rays.

• Far too massive to be a white dwarf or neutron
  star.
• The simplest interpretation is
• A 30 M? star and a 7 M? black hole

Measured orbital motion of HDE 226868.
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Evidence for BH
A disk of dust fueling a massive black hole in
the centre of a galaxy.
The speed of the gas around the center indicates
that the object at the centre is 1.2 billion
times the mass of our Sun.
800 light years
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Signature of a Black Hole
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Thanks to the following for allowing me to use
information from their web site Nick
Stobel Bill Keel Richard Pogge NASA
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