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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!