Download Part I Light, Telescopes, Atoms and Stars

Week 3
The Sun and Stars
Part I
Light, Telescopes, Atoms and
Stars
The Light of Astronomy

Electromagnetic Radiation
For the most part - all astronomical
observations are at distance

•
E-M radiation is our link
Let there be light





Electrical wave perpendicular to Magnetic Wave
Travels 300,000 km/sec (186,000 miles/sec) always
(in a vacuum)
The velocity of light is usually called ‘c’
Wavelength – longer = ‘redder’
shorter = ‘bluer’
The spectrum
Light in Astronomy

Wave Particle Duality
– Depending on how you measure/observe light
– it seems to act like a wave sometimes and a
particle (photon) sometimes
Our intuition says this can’t happen!
 Everything in the subatomic world acts
like this.
 Another way E=mc2 works!
 Particles vs. Waves????

Quantum Leap
Quantum Tunneling
Picture a wall with a slit…

Put a light bulb on one side and look at the
image made on the wall on the other side of
the wall.
 What do you expect to see?
One Simple Slit
One Slit version 2
One bright
spot.
But Light acts as a wave too…
Now what about two slits in
the wall?
The diffraction Pattern for
2 slits in the wall…
What is happening…
The truth behind 1 slit:
http://www.phys.hawaii.edu/~teb/optics/java/slitdiffr/
What if you allow one electron
a week to hit the ‘wall’
between two slits?
Week 1
Week 2
Electrons over
time
Week 3
Week 4
Week 5
How Light Works:
Light

E=hc/lamda --- Energy in Light
– h=Plank’s Constant 6.6262X10-34 joule sec
– lambda = wavelength, c = speed of light
– Frequency (Hz) = c/lamda (m)
 e.g. 89.5 MHz (FM) = 335 cm
 Short wave Radio 41m = 7.1 Mhz











Shedding More Light on It
See figure on next frame
To the right = longer wavelengths
Below AM = Power Cycles (wall current
frequency 60Hz Hz = cycles or waves per sec.)
AM-FM, VHF, UHF
Microwave
Infrared
Visible
Ultra-Violet
X- Rays
Gamma Rays
Cosmic Rays (particles)
HIGH ENERGY
Low Energy
Light and Us

The Human Eye
Light and Astronomy
Optical Telescopes optics
Made to operate in 400-700nm range only
 Elements of a telescope
•
Focal Length
•
Primary / objective
Eyepiece (camera/CCD/human eye)
•
The Eye and the Telescope
The Upside(down) of it

This needs to be corrected in binoculars or
terrestrial binoculars or telescopes.
 Is NOT worried about in telescopes.
A camera

Like the
eye
Upside down!
Digital Images

This is how amost ALL astronomy is done
today.
 Computers can help!
Telescopes

Two kinds of telescopes
 All based on the glass or mirror that FIRST
gathers the light
 Called the objective
• Lens - refractors
• Mirror - reflectors
Telescopes

Refractors
• First design of telescope
• Glass in end catches the light
• Focuses it down to eyepiece (lenses) at the back
of the tube.
• One piece and sealed
Telescopes
• Expensive and heavy
• Hard to keep aligned
• Chromatic Aberration
Telescopes

The “Power” of a telescope
• NOT the most important feature of the telescope
• Most important = Light Gathering Area = size of the objective
•
•
•
•
•
•
(mirror or lens that first gets a hold of the light)
Larger objective = more rain by r2 relation (area of a circle)
A=pi*r2
Comparison of light gathering power = ratio of areas
8” vs. 4” = 82/42 = 64/16 = 4X more light gathering power
Objective size also yields resolving power
Magnification comes from

Focal length telescope/ focal length of the eyepiece
(printed on the side of eyepiece)
• Smaller chip of glass in eyepiece = more magnification
Telescopes
 Reflectors

see next frame
Newtonian,Prime Focus, Cassegrain, Schmidt-Cassegrain




Newtonian = light out of side near front by diagonal mirror
Prime Focus = Big telescopes or cameras only, observer
INSIDE light path
Cassegrain = light out back with parabolic mirror
Schmidt-Cassegrain = light out back with spherical mirror and
corrector plate that starts the light focusing (sealed)
+ a minor variation, Coude’
Telescopes

Getting through the atmosphere
– Resolving power messed up by atmospheric turbulence


= Atmospheric Seeing = twinkling of stars
alpha = 11.6/D (D = mirror diameter in cm’s).
– Transparency (haze and clouds and sky glow)
– Light Pollution (from cities/outdoor lighting)
– Wind
– Local Temperature Effects
– Expansion/Contraction
– Dew
How they are used

Visual Observations (not scientifically
often)
 Imaging – pictures for study and beauty
 Spectroscopy – looking at the makeup of
the spectrum
 Timing – occultations, variable stars
 Visible and non-visible frequencies
Telescope Mounts

Alt-Az Mounts
– = Altitude and Azimuth motions only
 Altitude = straight up and down
 Azimuth = back and forth horizontally
– Lighter and cheaper
– Easier to set up in the field
– Easier to maintain
– Harder to track the motion of the sky
 Computers help with this now
Telescope Mounts

Equatorial Mount (German Equatorial Mounts)
– One axis points to the north celestial pole =
– Mount is tilted equal to your latitude
 You have to adjust it when you move more than 50 miles north or
south of your favorite spot
– Sometime more wobbly than alt-az
– Tracks the sky simply around one axis
– A sidereal clock can drive the gear (no computer necessary)
– Coordinates on mount can be set to match coordinates on start
maps and charts
– Alignment is necessary for it to work (North Pole axis right on).
– Good for photography and star parties
Getting a better Look


Mountain Top Locations are best (less seeing and better transparency year
round)
Adaptive Optics (New-Generation Telescopes)
•
Old telescopes = large thick blanks of glass = tons! (200 inch Hale Telescope
on Mount Palomar = 14.5tons)


•
Temperature problems – uneven expansion
Sagging at low altitude tilt
New telescopes have a computer and laser sensor system that constantly
checks the shape of the mirror and adjusts it

Segmented Mirror is one type
Looking good

Another type is a thin deformable mirror
• Mirror shape can also be rapidly updated to reduce the
effect of seeing (unblurring the star images).
Telescope Improvements


Photographic Plates were the standard… but now;
CCD cameras
• =Charge-Coupled Device (where we get modern video cameras
from)
• Digitizes data which is stored rapidly on computers. The images
can be manipulated later

Spectrographs are
also in common use
• Break the star or nebula
light up into a spectrumelement lines become
visible (more on this later)
• Stored on film or CCD
The
Biggest
Telescopes
Top Scopes

The Hubble Space Telescope
(and why)
• 96 inch mirror
• Largest orbiting telescope ever
built
• Not a very large telescope
but it has NO seeing or
transparency problems induced
by the atmosphere. Also no
day (except part of every
~ 90 minute orbit)
or weather problems!
•
•
•
Places:
Mountain Tops
Airplanes
Other types of Telescopes

Other (research) telescopes
• Radio






A big dish (larger than light due to larger wavelength)
Pointing picks up a point value of radio energy
A computer puts it together into a picture later below
Can operate in the day and under clouds
Can pick up clouds of hydrogen gas and other non-stellar emissions
Radio interferometry
Radio Telescopes
Additional Telescopes – near
visible light
• UV and IR
 The atmosphere absorbs UV (ozone) and IR
radiation (water vapor)
 Space based telescopes and high mountain (Maouna
Kea and Chile and airplane and balloon borne
telescopes are the only useful tools
 IR = IRAS (Infrared Astronomy Satellite – early
1980’s)
 UV = International Ultraviolet Explorer (IUE) 1978
High Energy Telescopes
• X-Ray & Gamma Ray Telescopes
 Also space, balloon and aircraft based
 X-Ray = Einstein Observatory
 Metal Lenses
 More details later
The Chandra X-Ray
observatory (satellite)
TELESCOPES
OF THE FUTURE!
The TMT- Thirty meter telescope
E-ELT : European Extremely
Large Telescope
(42m = 4x larger than
present day largest)
Future Telescopes – The OWL
The 100 m OWL
(overwhelmingly
large telescope)
James Webb Space telescope
Launch June 2013 – 6.5 m
½ the mass of Hubble’s mirror, 6X
More On Light

Atoms
– Joseph von Fraunhofer early 1900’s.
 Found 600 dark lines in the solar spectrum
 The lines are different for each element (like a
fingerprint)
 This opened up the study of the universe AND the
generalization of physics
Inside the Atom
– The atom
 a positively charged nucleus
– Protons (heavy)
– Neutrons (heavy)

A cloud of negative charge around it
– Electrons (light)
Light topics

Atoms
– Usually have the same number of neutrons, protons and
electrons (electrically neutral)
– An Isotope = missing neutrons
– An Ion = missing electrons
– Scale
Size 2.5 million
on pin head
Odd Atoms
Phases
of Matter
HOT
It just depends on
the temperature!
COOL
Lighter topics
– Colliding Atoms stick via sharing electrons (when some
are missing) makes molecules
– Within a single atom- the Coulomb force (positive
charge attracts negative charge) holds the electrons to
the atom = binding energy
– The electrons ‘orbit’ at certain distances from the
nucleus (a model!) – these orbitals have only certain
steps see right

Remember the ‘orbit’
picture is not really
accurate… they are in
clouds that have
indistinct shells they
exist in.
Atoms

Absorption Lines
Emission/Absorption Lines
– The orbit number and jump energies are
referred to as energy levels
– If energy (light/photon) hits the atom and gives
it energy, then the electron(s) jump to a higher
orbit/energy level = an excited level
– If certain energy photon is taken out of light
(equal only to a perfect single or multiple orbit
jump/ energy level) then there is a dark line
left in the continuum
– Absorption Line
Atoms – emissions lines
– Once an atom is excited- it wants to return to ground state
–
–
–
–
(lowest possible energy, lower orbitals filled)
Atoms can get energy from collision as well (heating a bar on
one end)
The emitted light is only in the energies (wavelengths) that the
electrons can hop down (depends on the atom)
This gives us Emission Lines
Whenever an electron drops to a
lower level, it emits E-M radiation
at the frequency of the energy drop
Every atom has it’s own
Fingerprint!
Real objects… the Orion Nebula
Radiation/Temperatures

When we heat an object, the atoms begin to move
around faster and faster and collide.
 Electrons get knocked to higher and higher levels
the more heat we add (increasing the temperature).
Eventually it begins to glow (this is emitted
radiation from excited electrons dropping down
and emitting radiation.
Radiation and Temperature

This gives a continuum of radiation
called Black Body Radiation
 The amount of radiation emitted
from a Black Body Emitter = a
tilted curve [right] with a peak
wavelength that is ONLY
temperature dependent
 Maximum wavelength=
3,000,000/Temperature (K)
– The hotter something is the
‘bluer’ it looks (white hot)
JUST LIKE THIS:
You glow too!!
Recapping Radiation

Wien’s Law (Peak Radiation)
– wavelength = 3,000,000/Temp(K)
– Total amount of energy = Stefan-Boltzmann Law see
back 3 frames : Energy is proportional to (temperature)4
– So the hotter something is the more overall energy you
get out of it

Recap Figure

There are three main groupings of spectral lines in
hydrogen (pg 99 Fig top left) based on their starting level.
The Balmer series is the only one that produces visible
light lines
Spectral Classification

We can use these energy laws to classify
stars. Hotter stars have higher peak
emissions and more overall energy
 The surface energy is what we are usually
interested in (we see that part)
Grouping Stars

Stars range typically from 2,000K to 40,000K
 2000K = red , 40000K = white/blue
 The Balmer series is a better thermometer
 Cool stars = weak Balmer series lines (less
ionizations) Hot stars = weak lines (everything
ionized), Medium stars = strong lines (correct
amount of energy for these lines in the collisions
caused by the temperature)
Spectral Classification Cont.
During the 1890’s labeled stars from A to Q with
incomplete knowledge of the cause of spectral
lines (the elements and temperatures)
 When it got straightened out, groups merged and
were deleted and reorganized from cool low mass
stars to hot high mass stars

History Stays With Us





O,B,A,F,G,K,M (O=big hot star, M=small cool star)
Oh Be A Fine Girl (Guy), Kiss Me
Later the cooler classifications (with metal lines) R,
N, S were added to the right.
Oh Be A Fine Girl, Kiss Me Right Now Sweetheart
Oh Brutal And Ferocious Gorilla, Kill My Roommate
Next Saturday
Spectral Sequence

Astronomers further subdivided the sequence
OBAFGKM(RNS) into subclasses 0 (hottest) to
10(coolest)
 So an A3 is hotter than an A7
 Shows the
spectra for the
major half and
whole spectral
classification steps
Spectral Sequence

Our sun is a G2 star with a temperature of
5800K
 R,N,S are variations of M, but now (1998) a
cooler type of star called an L dwarf has
been observed that extends the
classifications one more full notch cooler
More information from spectra

Doppler Shifting
– Similar to sound,
light experiences a
Doppler shift when
the source is
approaching or
departing from
the observer
Doppler Shift
– Approaching object blue shifts the
emission/absorption lines out of place toward
shorter wavelengths (higher energies),
retreating object red shifts the lines out of place
toward longer wavelengths (lower energies)
– The same as Doppler Radar but with visible
light rather than microwave energy (remember
it’s all the same E-M spectrum!)
– This allows us to measure the radial velocity of
stars, gas clouds, and galaxies as well as the
ROTATION of stars and galaxies!
Spectral Lines and the
Doppler Shift = Velocity!
Week 3 From Our Sun to
Black Holes
Part II
The Sun
The SUN – an average star
Like a star- it’s a ball of mainly Hydrogen and Helium
gas in a balance between downward gravity and
outward pressure
It is in the middle of the field in size, temperature,
mass and life (compared to other stars – more later!)
Spectral Class: G2
Structure
Sol
It’s all hot gasses, but does have a distinct structure
Near the center (the core) of the sun nuclear fusion is
proceeding generating tremendous energy (4.7 million tons
per second from E=mc2 and 3.9x1026 J/s luminosity)
 This is surrounded by the radiation zone – photons must take
the energy out – random walk – 500,000 years!
Then the convective zone (like thunderstorms all crammed
together)
Then the photosphere
The Sun continued

The Photosphere
– The visible surface of the sun
– Is less than 500 km deep and has a temperature of about
6000K
– Is really very low density gas (3400x less than atmospheric
pressure) 10% of the way to the Sun’s center would bring us
to 1 atmosphere
– Has granulation (top of the convective cells) each cell is the
size of Texas and lasts 10-20 minutes see below
Sun Stuff

The Chromosphere
– Next layer of ‘atmosphere’ up
– Only visible at total lunar eclipse or from space
– 10,000K to 1,000,000K or more!
– Spicules= bright flame like structures 100-
1000km in diameter (hair like)
The Chromosphere

More Sun Stuff
The Corona
– Beyond the Chromosphere – extends out into the Solar System



Up to 3,000,000 K !
Bends to the Sun’s Magnetic Field – large hair like appearance at total solar
eclipse below
Escaping ionized atoms become the Solar Wind that blows past the Earth at
300 to 800 km/s with gusts to 1000 km/s

Other Features
More Sun Stuff
– Helioseismology see below
– Using Doppler shift data- they see the sun rings like a
bell (oscillates with definite 3-D harmonics)
Sunspots

Sunspots
– Cooler areas (about 4240K) appear dark ONLY in
comparison to the whole disk
Sunspots from the side
The Sun continued
Sunspots
Located on the photosphere
Darker because of the Black Body Spectrum /Stephan
Boltzman Law
If the whole sun became a sunspot it would shine with
the brightness much more than that of a full moon and
have an orange-red color
The Quiet sun
May 2008 near
solar minimum
The spotty Sun
Butterflies
 Sunspot numbers change over time- with
an 11 year cycle (22 year with polarity
switch)
 Zero to 100 (minimum to maximum)
 At the start of each cycle the sunspots
start at high latitudes (near the poles)
and migrate toward the equator at the
peak
 The chart of time and latitude
= Maunder Butterfly Diagram
400 years of sunspots
11,000 years of reconstructed
sunspot data
Sunspots




A sunspot is often larger than the Earth
Outer part = penumbra
Darker inner part = umbra
Very few sunspots from 1645 to 1715
= Little Ice Age 1430 – 1850
 CAUSE?
 Differential Rotation
 Dynamo Effect = wrapping up
of magnetic field lines
Sun Features Continued
 Prominences and Flares
 Huge hoops (famous Solar Storms) right
 (Incredible Picture lower right)
 Causes Aurora
 Aurora Borealis & Australis
 Coronal holes –where parts of the loops keep going
 These affect the Earth= communication problems, Aurora
 Climatic Effects ,
The sun creates Ozone = UV blocking
– Sunspots and Weather
– Milankovitch hypothesis



Orbital variations 100,000 year shape change
Precession causes Earth’s axis to sweep a circle every
26,000 years
Axis tilt changes over 41,000 years
Our Sun is a Star
So on to other Stars…
Properties of Stars

Our sun is 8.4 light minutes distant
 The nearest star to us is over
4 light years away
 1 light year is about 5.9 trillion miles

Distances from us (measurements)
– Surveyors = a baseline and two angles
(example)
– Astronomers do the same trick using more distant stars to
measure the angle as the earth moves around the sun stellar
parallax
Distances to Stars
– Approximations allow us to get distances from a
–
–
–
–
simple equation distance (AU) = 206265/p (angle)
If 1 parsec is defined as distance that 1 AU shift =
1 arc second, then equation becomes
1 (pc) = 1/p (angle) (EASY!)
1 parsec = 3.26 light years
Smallest parallax measurable = 0.02 seconds of arc =
50pc (due to atmospheric blurring/seeing)
Hipparcos satellite = .001 sec of arc = one million
measured stars
Star Brightness

Apparent Brightness = how bright a star appears
from earth usually given the letter ‘m’ (small m)

Actual (Intrinsic) Brightness


When we look at a star, we see brightness based on the
flux of energy (J/sec*m2) or (W/m2)
Every two times the distance out, you have 1/4th the
flux / brightness
Star Brightness
– We want to compare all stars with each other, by
–
–
–
–
–
‘bringing’ them to a standard distance (mathematically)
and stating how bright they would be there
That distance is defined as 10 pc = Mv
Mv M is for absolute magnitude, the v is for visual
Found by measuring the apparent magnitude (m) and
the distance (using parallax)
m-Mv=-5+5log10(d) with d in (pc) don’t sweat this
detail!
From this we can calculate the actual Luminosity

Stars –Luminosity
Diameters of Stars
– Now we know luminosity, and we know the temperature
(from the peak radiation = Wein’s Law);

We can find the radius of a star (amazing no?)
–
L/L(sun)=(R/Rsun)2*(T/Tsun)2
again- details you DON’T need to know
– Allows us to make the Hertzsprung-Russell (H-R) diagram = one of the most
important findings/tools/visualizations in all of observational astronomy
A detail you DO
need to know!!
The H-R diagram in color
The H-R Diagram

The main sequence (sun just below the center)
– S shaped curve
– Dwarf stars
(strange terminology)

Other H-R Details
Other branches
– Giants, supergiants, white dwarfs – moral of the story: there is order to the
types of stars that can exist
– The order extends to
branches called
luminosity classes
– (The upper right corner in details)
– So now we have a new tool- we can tell the distance to a star if we know its
spectral classification (from the absorption lines) and its luminosity
(its apparent brightness and its luminosity (calculated)) -- this is called a
spectroscopic parallax
Masses of Stars
 For this we need to find binary stars




(very common- 2 of 3 stars in the sky are multiple star
systems!)
The two stars revolve around a common center of mass
The ratio of the masses = the inverse ratio of their
separation MA/MB=rB/rA
We can’t figure out the separate masses, but we can figure
out the total mass of the system
MA+MB= a3/p2 (a = separation in AU, p=period in years)
Binary Stars

Types of Binaries
– Visual binary system
– Spectroscopic binaries – pairs of Doppler
shifting
spectral
lines
– Eclipsing binaries – (can also be
spectroscopic)



Light curve right
Must be edge on as viewed from the Earth
Famous star = Algol
Binary Stars
– With eclipsing binaries we can see the size of stars by
the time it takes for one star to cover the other (with the
temperature/spectral type/and masses figured out, the
size gives us the complete picture!)
– We find a direct relationship between mass and
luminosity (except white dwarfs)
– In fact the relationship is L=M3.5
– Pg 151 Fig right side top and bottom Stellar
Populations
Stellar Populations
Star Formation
 Interstellar Medium
– In the Milky Way galaxy, we see great lanes of dust
and gas between the stars = the Interstellar Medium
– It is about 75% hydrogen, 25% helium with traces of
carbon, nitrogen, oxygen, calcium, sodium and even
alcohol, water and formaldehyde
 That and dust makes up ‘nebula’
Nebulae
 If a hot star is within a cloud of gas and dust and it
ionizes the gas, it glows = an emission nebula
 If the light just reflects off dust = reflection nebula
 If light passes through gas and dust- blue light is
reflected – we see the star redder than it should be
= interstellar reddening
 We can get information on the interstellar medium
by what kind of light we do or don’t get from the
stars
Stellar Formation
 Most interstellar clouds
seem to be stable (slight
outward thermal
pressure against gravity)
 A shock wave is needed
to start collapse (from a
supernova = death of a star)
Bok Globules

10-1000 stars are often formed (due to
fragmentation and instabilities) = a star cluster ;
collapsing cloud = Bok globules
Cloud to Disk
Protostars
As a cloud collapses – we get a protostar (an
object that will become a star)
 The contraction and formation of the star can be
plotted on the H-R diagram

T-Tauri Stars
– Path to main sequence short for massive stars- very
long for low mass stars
– This process is still not
clearly understood
– Early stars (just after birth) clearing
out the dust and gas left over are called
T-Tauri Stars lower left
– The disk of expelling gas that changes its
brightness in a few years = Herbig-Haro
objects
far right
Energy Generation in a Star

To understand the largest structures in the
universe- we need to understand the smallest scale
laws
– There are 4 forces known (all are somewhat important
here!)




The strong nuclear force (holds the nucleus together)
The weak nuclear force (radioactivity)
The electromagnetic force (light)
The gravitational force (gravity)
Energy Makin’
– Einstein lead us to work with nuclear fission and
nuclear fusion



Fission = breaking apart heavy atoms – uranium etc.
Fusion = joining of smaller atoms – hydrogen
Fusion – How the Sun and Stars
Work
Energy from the Core
– Hydrogen Fusion
 4 hydrogen nuclei weigh 6.693x10-23kg
-23
 1 helium nucleus weighs 6.645x10 ke
 Difference is .048x10-23kg = photons that start a race out of
the center
 E=mc2 shows us that is 0.43x10-11 J = lift a fly .001 inch in
the air
 BUT we get 5 million tons converted to energy a second
 Gives us 10 billion years until the hydrogen runs out
Inside the Stars continued

Sideline: The Solar Neutrino Problem
• Measurements of the neutrinos
vs. solar's interior models in the
Standard model the Neutrino is
massless; fixed ratio between
the number of neutrinos and the
number of photons in the
cosmic microwave background
Observation
•We Only detected between 1/3
and 1/2 of predicted number;
•NEW! Neutrinos with mass
change type, We have now
detected multiple neutrino types

Inside the Stars continued
When the hydrogen is used up, then the star must
begin to ‘burn’ helium
– 2 Helium make Beryllium
– A Beryllium atom and a helium can make a carbon
– All releasing energy- greater pressure and
temperature are needed to overcome the repulsion of
the positive charges (Coulomb barrier) – messy – eh?!
Stellar Structure


Stellar Structure
A star is a balance between downward
weight (gravitational pull) and outward
pressure (from heat)
– The pressures and such do determine
how energy gets out
– Energy Transport



Conduction
Radiation Primary means in
much of inner portion of the star
Convection (examples)
The outer portion of the star
Main Sequence Stars

Less massive stars don’t need as much ‘burning’ in
their core to hold up their lesser mass,
– less burning = longer life

More massive stars burn a tremendous amount of
energy to fight the gravitational pull to collapse
 If the sun stopped making energy in its center- we
wouldn’t notice much on the outside for about
100,000 years, but then we would see it start to
collapse
Main Sequence Life

The Life Cycle
– When a protostar stops contracting and begins
to fuse hydrogen, it stabilizes (enters the main
sequence curve)
– It spends 90% of its life in this stable state
– A star must have a limiting mass to have
pressure and temperature at the center high
enough for fusion = .08 solar masses
Main Sequence Stars Continued

Below this you get brown dwarfs (heat of contraction
only) – Jupiter is sub-brown dwarf
 It takes 4 hydrogen to make a helium. Each helium
exerts the same pressure as 1 hydrogen, so the core
begins to contract- so reactions happen faster –
heating the star- so it expands and gets a bit brighter
and hotter
 Years on the main sequence vary from 56x109 years
for M0 stars to 1x106 years for O5 stars


Stars use hydrogen for 90% of their lifetime
Low mass stars die quiet deaths, high mass stars die VIOLENT
deaths!
– Very important energy diagram!
See next frame for Iron!
Ages of
Stars
clusters
and the H-R
diagram
Aside: How DO
we know how old
stars are?

The Death of Stars
GIANT STARS
– When the hydrogen is nearly gone- helium fills the core like ash
– Energy generation starts to shut down, and the upper materials start
to fall on the core (the star contracts) = more heat
– Hydrogen starts to fuse in a shell around the helium core, this
expands outward
A
star
dies
– The star expands (Sun like stars expand 10-100x, larger stars
expand to 1000x the sun’s diameter
– The outer part of the star cools, but it becomes larger (= brighter)
so you see the star leave the main sequence see below
– Degenerate gas forms at the star core (gas where the electrons are
all forced to fill to the maximum number of electrons close to the
nucleus as possible).


The gas has a consistency of steel
A change in temperature
= no change in pressure
The Death of Stars II

Giant Stars
– A teaspoon of this degenerate helium gas would weigh
as much as an automobile
– The temperature rises while the pressure stays the
same= a runway explosion when the helium can fuse




Enough energy to outshine an entire galaxy for a few minutes
The star does NOT show any outward changes
Degenerate gas turned back to normal- helium fusion begins
normally
Helium burns with a shell of hydrogen around it
The Death of Stars III

Death of Low & Medium Mass Stars
– Greater than .08 Solar Masses to .4 Solar
Masses (Low Mass)




Totally convective
Slow Burn
Slow contraction
Become hot and small = white dwarfs

The Death of Stars IV
Medium- Mass Stars
– .4 Solar masses to 4 Solar masses
– Can ignite hydrogen and helium, but not carbon
– Become red giants, but don’t mix well (little core convection)
– Make Planetary Nebula See Next Frame
– End in white dwarfs (no nuclear energy production- just collapse
heat – cooling), eventually become black dwarfs pg520-524
– They are hot but small (Fig bottom rt.)
– Mass MUST shed mass
to drop below 1.4
Solar Masses
(Chandrasekhar Limit)
White Dwarfs (our Sun’s end)

We can
detect them
if they are
in a close
binary
configuration
 Make Novae
(not Supernovae)
Life on Earth when the sun
dies?
The Death of Massive Stars

Massive Stars
 Can pass Carbon and experience Carbon
Detonation
– Then Oxygen, neon, magnesium, sulfur and
then silicon
– Hydrogen 7,000,000 years, Helium 500,000
years, Carbon 600 years, Oxygen 6 months,
Silicon 1 day
– Then IRON!
The Death of Stars IV





Iron is endothermic– takes energy instead of releasing it
(remember that from earlier?)
Core cools when temperature is high enough to start iron
fusing
Core collapses in less than 1/10th of a second
A neutron star or black hole is made and the outer shells
of the star explode off into space in a tremendous
explosion due to the rebound off the core
The Supernova!!
Supernovae

The core produces more energy than the entire
visible galaxy for a few seconds + a blast of
neutrinos
 Remains expand at 1400 km/sec
 Famous Supernovae
– 1054AD (Crab Nebula in Taurus)
– 1572 AD (Tycho's supernova)
– 1604 AD (Kepler’s supernova)
– SN1987A (in the Large Magellanic Cloud)
The Crab Nebula – Stellar Remains
Here is where the ‘stuff’ is made
Stellar Remains:Neutron Stars

Made of a star that started at just a few solar masses,
but the remains are crushed down to only 10km in
size
 Protons and electrons jammed together in
tremendous pressure- degenerate matter again – pure
neutron material
 Predicted in 1932 by the Russian physicist Lev
Landau
Neutron Stars

A sugar cube size of the neutron star material
would weight 100 million tons
 VERY hot at first (millions of degrees) and slow
to cool (radiation from surface)
 VERY rapid spin (conservation of angular
momentum)
 Magnetic field about 10 million times stronger
than the Sun’s = jets of energy out the magnetic
poles ‘
Neutron Stars

Lighthouse model,
 Pulsars! (LGM =
Little Green Men) .033 to
3.75 second periods
 Slight increases = quakes on
the surface
 Fastest = 642 rotations a
second = 40,000 km/sec =
flatten and almost can tear it
apart
Neutron Stars II

Binary Pulsars– If a binary system has one star become a neutron star AND the
other one begins to expand (become a giant) its outer gasses can
cross the
gravitational balance between
the stars and begin to fall onto
the neutron star making an
accretion disk
– Material builds up in a disk and
can detonate = nova or X-ray or
gamma ray bursts or jets
– Gamma ray bursts occur daily and are probably from VERY
intense magnetic field (100x stronger than normal neutron stars)
called magnetars (two known both about 10,000 ly away!– one on
Aug 28, 1998 ionized the Earth’s upper atmosphere and disrupted
radio communication world wide for a while)
Like a
Lighthouse
The biggest stars don’t stop at
Neutron Star remains…
Black Holes
Black Holes

Escape Velocity
– From earth = 11 km/second (25,000 mph)
– From earth on top of 1000 mile tower = 8.8 km/second
(20,000 mph)
– Enough matter in one location then the escape velocity
from near the object can be the speed of light or greater
= you aren’t going anywhere!
Black Holes
– Schwarzschild Black Holes
 VERY massive objects (star core >3 solar masses)
keeps collapsing = a singularity (a point in which
all the matter resides- no force exists to hold it up)
 The point around the black hole where the escape
velocity is equal to the speed of light = the event
horizon (no event inside that boundary is EVERY
visible again) right
 The Schwarzschild Radius
is simply based
on the mass of an object
–
–
–
–
Rs=2GM/c2
A 10 solar mass star = 30 km
Our Sun = 3 km
The Earth = .9 cm
Black Hole Trivia


If the sun became a black hole right now – nothing would change
here except we would get cold. It does NOT suck in all matteronly stuff that gets too close (just a few 10’s of km’s for the Sun
would be in danger)
Finding Black Holes
– Binary stars with High Mass
– X-ray source (accretion disk)
– Six candidates =
Page after next
Into the Black Hole



Time Dilation
Gravitational red-shift
Tidal Forces
– Bad news
Spaghettification
Black Holes
Cygnus X-1 artists conception
Current Black
Hole
Research
Current Black Hole Research
Not always an Event Horizon

Slow collapse might let space polarize (Neutron
Stars –Pauli exclusion principle)
 Quark stars/Strange stars (strange particles, not
weird)
 Boson star/ Glue Ball (gluons)
(another collection of atomic particles nearly a
black hole/black star)
 Q-balls or Q star – even closer to a black
hole/black star
 Black Stars
Current Black Hole Research
Current Black
Hole
Research
Gamma Ray Bursters (new)





Mysterious – brief (seconds) flashes seen visibly
by careful amateurs.
Compton Gamma Ray Observatory Verified
Afterglow identified visually using big
observatories… found in distant galaxies and outer
reaches of the universe
Light from the full spectrum blasts out
Most powerful explosions in the universe! Energy
of 10 million billion suns released in a few
seconds. Outshines the energy output of 10% of
the universe for a moment!!!
More on GRB’s

Collision of two neutron stars or black
holes?
 A star being ripped apart by a black hole?

Or more exotic causes? Matter/Anti-matter
collisions? White Holes (exit region of a
rapidly rotating black hole)?
There are still mysteries to be
discovered out there!