Week 3 The Sun and Stars

Week 3Week 3The Sun and StarsThe Sun and Stars

Part I

Light, Telescopes, Atoms and Stars

The Light of AstronomyThe Light of Astronomy Electromagnetic Radiation For the most part - all astronomical

observations are at distance• E-M radiation is our link

Let there be lightLet 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 AstronomyLight 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 LeapQuantum Leap

Quantum TunnelingQuantum Tunneling

Picture a wall with a slit…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 SlitOne Simple Slit

One Slit version 2One Slit version 2

One bright spot.

But Light acts as a wave too…

Now what about two slits in Now what about two slits in the wall?the wall?

The diffraction Pattern for The diffraction Pattern for 2 slits in the wall…2 slits in the wall…

What is happening…What is happening…

The truth behind 1 slit:The truth behind 1 slit:

http://www.phys.hawaii.edu/~teb/optics/java/slitdiffr/

What if you allow one electron What if you allow one electron a week to hit the ‘wall’ a week to hit the ‘wall’

between two slits?between two slits?

Electrons over Electrons over timetime

Week 1

Week 2

Week 3

Week 4

Week 5

How Light Works:

LightLight

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 ItShedding 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 UsLight and Us

The Human Eye

Light and AstronomyLight 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 TelescopeThe Eye and the Telescope

The Upside(down) of itThe Upside(down) of it

This needs to be corrected in binoculars or terrestrial binoculars or telescopes.

Is NOT worried about in telescopes.

A cameraA camera

Like the eye

Upside down!Upside down!

Digital ImagesDigital Images

This is how amost ALL astronomy is done today.

Computers can help!

TelescopesTelescopes

Two kinds of telescopes All based on the glass or mirror that FIRST

gathers the lightCalled the objective

• Lens - refractors• Mirror - reflectors

TelescopesTelescopesRefractors

• 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


• Expensive and heavy• Hard to keep aligned• Chromatic Aberration

TelescopesTelescopes 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


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’+ a minor variation, Coude’

TelescopesTelescopes 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 usedHow they are used

Visual Observations (not scientifically often)

Imaging – pictures for study and beautySpectroscopy – looking at the makeup of

the spectrumTiming – occultations, variable starsVisible and non-visible frequencies

Telescope MountsTelescope MountsAlt-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 MountsTelescope 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 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 goodLooking 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 ImprovementsTelescope 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 spectrum- element lines become visible (more on this later)

• Stored on film or CCD

TheThe Biggest Biggest


Top ScopesTop 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 TelescopesOther 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 TelescopesRadio Telescopes

Additional Telescopes – near Additional Telescopes – near visible lightvisible 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 TelescopesHigh 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 The Chandra X-Ray observatory (satellite)observatory (satellite)

TELESCOPESTELESCOPES

OF THE FUTURE!FUTURE!

The TMT- Thirty meter telescopeThe TMT- Thirty meter telescope

E-ELT : European Extremely E-ELT : European Extremely Large TelescopeLarge Telescope

(42m = 4x larger than (42m = 4x larger than present day largest)present day largest)

Future Telescopes – The OWLFuture Telescopes – The OWL

The 100 m OWL (overwhelmingly large telescope)

James Webb Space telescopeJames Webb Space telescope

Launch June 2013 – 6.5 m ½ the mass of Hubble’s mirror, 6X more area.

More On LightMore On LightAtoms

– 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 AtomInside the Atom– The atom

a positively charged nucleus– Protons (heavy)– Neutrons (heavy)

A cloud of negative charge around it– Electrons (light)

Light topicsLight 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 AtomsOdd Atoms

PhasesPhases of Matter of Matter

It just depends on

the temperature!

HOT

COOL

Lighter topicsLighter 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 reallyaccurate… they are inclouds that have indistinct shells theyexist in.

Atoms Atoms Absorption LinesAbsorption 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 – Atoms – emissions linesemissions 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 Every atom has it’s own Fingerprint!Fingerprint!

Real objects… the Orion NebulaReal objects… the Orion Nebula

Radiation/TemperaturesRadiation/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 TemperatureRadiation 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!! You glow too!!

Recapping RadiationRecapping 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 ClassificationSpectral ClassificationWe 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 StarsGrouping 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.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 UsHistory 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 SequenceSpectral 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 SequenceSpectral SequenceOur sun is a G2 star with a temperature of

5800KR,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 spectraMore information from spectraDoppler Shifting

– Similar to sound, light experiences a Doppler shift when the source is approaching or departing from the observer

Doppler ShiftDoppler 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 Spectral Lines and the Doppler Shift = Velocity!Doppler Shift = Velocity!

Week 3 From Our Sun to Week 3 From Our Sun to Black HolesBlack Holes

Part II

The SunThe 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

SolSolStructure 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 continuedThe 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 StuffSun 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 StuffMore 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

More Sun StuffMore Sun Stuff Other Features– Helioseismology see below – Using Doppler shift data- they see the sun rings like a

bell (oscillates with definite 3-D harmonics)

SunspotsSunspots

Sunspots– Cooler areas (about 4240K) appear dark ONLY in

comparison to the whole disk

Sunspots from the sideSunspots from the side

The Sun continuedThe Sun continued

Sunspots

Located on the photosphereDarker because of the Black Body Spectrum /Stephan

Boltzman LawIf 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 sunThe Quiet sun

May 2008 near solar minimum

The spotty SunThe spotty Sun

ButterfliesButterflies 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 sunspots400 years of sunspots

11,000 years of reconstructed 11,000 years of reconstructed sunspot datasunspot data

SunspotsSunspots 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 ContinuedSun 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 StarOur Sun is a StarSo on to other Stars…So on to other Stars…

Properties of StarsProperties 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 StarsDistances 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 BrightnessStar 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 BrightnessStar 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 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 The H-R diagram in ccoolloorr

The H-R DiagramThe H-R Diagram The main sequence (sun just below the center)

– S shaped curve– Dwarf stars

(strange terminology)

Other H-R DetailsOther 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 StarsMasses 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 StarsBinary 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 StarsBinary 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 PopulationsStellar Populations

Star FormationStar 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’

NebulaeNebulae

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 FormationStellar 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 GlobulesBok Globules 10-1000 stars are often formed (due to

fragmentation and instabilities) = a star cluster ; collapsing cloud = Bok globules

Cloud to DiskCloud to Disk

ProtostarsProtostars 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 StarsT-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 StarEnergy 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’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 CoreEnergy from the Core– Hydrogen Fusion

4 hydrogen nuclei weigh 6.693x10-23kg 1 helium nucleus weighs 6.645x10-23ke 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 continuedInside the Stars continuedSideline: 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 continuedInside 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 StructureStellar 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 StarsMain 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 LifeMain 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 ContinuedMain 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 starso 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 Ages of Stars Stars

clusters clusters and the H-R and the H-R

diagramdiagram

Aside: How DO we know how old stars are?

The Death of StarsThe 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 diesA 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 IIThe Death of Stars IIGiant 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 IIIThe 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 IVThe 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)White Dwarfs (our Sun’s end)

We can detect themif they are in a closebinaryconfiguration

Make Novae(not Supernovae)

Life on Earth when the sun Life on Earth when the sun dies?dies?

The Death of Massive StarsThe 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 IVThe 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!!

SupernovaeSupernovae

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 RemainsThe Crab Nebula – Stellar Remains

Here is where the ‘stuff’ is madeHere is where the ‘stuff’ is made

Stellar Remains:Neutron StarsStellar Remains:Neutron StarsMade 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 StarsNeutron 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 StarsNeutron 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 IINeutron 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 The biggest stars don’t stop at Neutron Star remains…Neutron Star remains…

Black HolesBlack 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 HolesBlack 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 TriviaBlack 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 matter- only 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 HoleInto the Black Hole Time Dilation Gravitational red-shift Tidal Forces

– Bad news

Spaghettification


Cygnus X-1 artists conceptionCygnus X-1 artists conception

Current Black Current Black Hole Hole

ResearchResearch

Current Black Hole ResearchCurrent Black Hole Research

Not always an Event HorizonNot always an Event HorizonSlow 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 ResearchCurrent Black Hole Research

Current Black Current Black Hole Hole

ResearchResearch

Gamma Ray Bursters (new)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’sMore on GRB’sCollision 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 There are still mysteries to be discovered out there!discovered out there!

Documents

Week 3 The Sun and Stars