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Slide 2 February 18, 2003Lynn Cominsky - Cosmology A3501 Part I: Stars and Stellar Characteristics Part II: Stars that Go Boom July 22, 2004 Slide 3 February 18, 2003Lynn Cominsky - Cosmology A3502 Stars and Stellar Characteristics Seeing Stars Physical characteristics (distance, luminosity, mass, temperature, etc.) Life Cycles Creation of Elements Supernovae and Gamma-Ray Bursts Topics for the Day Slide 4 February 18, 2003Lynn Cominsky - Cosmology A3503 What do we know about stars? Slide 5 February 18, 2003Lynn Cominsky - Cosmology A3504 Case Study: Seeing Stars In this interactive exercise, we will examine a case study of how astronomers study stars We will use the scientific method to observe, ask questions, then re-observe, modifying our questions and knowledge as our investigation expands Slide 6 February 18, 2003Lynn Cominsky - Cosmology A3505 Case Study 1: The Stars, Like Sparks of Fire The Mighty Hunter Slide 7 February 18, 2003Lynn Cominsky - Cosmology A3506 Case Study 1: The Stars, Like Sparks of Fire Stars are points of light Different brightnesses Different colors Different distribution (many along Milky Way, not many at 90 degrees from it) Need distances to get physics, more understanding of their nature Some possible observations: Slide 8 February 18, 2003Lynn Cominsky - Cosmology A3507 How far away are the stars? How can you figure this out, given the tools of the time? Think of what you know from the first case study, and see if you can apply it. Case Study 2: The Stars, My Destination Slide 9 February 18, 2003Lynn Cominsky - Cosmology A3508 Case Study 2: The Stars, My Destination 0.12 0.5 1.6 2.1 4.7 6.0 10.1 Mag Lights Slide 10 February 18, 2003Lynn Cominsky - Cosmology A3509 Case Study 2: The Stars, My Destination Parallax Brightness (relative) [yes! Make blink] Colors (redder are farther) Size (oh really?) Need distances to get physics, more understanding of their nature Some possible methods: Slide 11 February 18, 2003Lynn Cominsky - Cosmology A35010 Case Study 3: The Lights in the Sky Are Stars Ogden claims to know the distance to Rigel! What assumptions has he made? Which are good, which are not? Is his distance estimate accurate? If not, do you think its too big or too small? Slide 12 February 18, 2003Lynn Cominsky - Cosmology A35011 Case Study 3: The Lights in the Sky Are Stars He remembers Rigels brightness accurately Being inside is same as outside Rigel is just like the Sun Some assumptions: Rigel is hotter, bluer, and bigger than the Sun. How does this affect his distance? Slide 13 February 18, 2003Lynn Cominsky - Cosmology A35012 Aside: Parallax Overview Parallax is an apparent shift Given baseline, can determine distance Gimme a thumbs-up! My thumb is 2 cm across and 68 cm away from my eye. From small angle formula: Apparent size (radians) = diameter/Distance 2 / 68 * (180 / pi) = 1.5 So anything the size of my thumb (1.5) is 34 times its own diameter away. Slide 14 February 18, 2003Lynn Cominsky - Cosmology A35013 Distances to Stars Parallax : determined by the change of position of a nearby star with respect to the distant stars, as seen from the Earth at two different times separated by 6 months. Slide 15 February 18, 2003Lynn Cominsky - Cosmology A35014 Parallax, parsecs and light years 1 parsec is defined as the distance at which a star would have a parallax angle of 1 arc-second 1 arc-second = (1 degree/3600) = (1 degree/3600) ( radians/ 180 degrees ) = 4.85 x 10 -6 radians 1 parsec = (1.5 x 10 8 km)/(4.85 x 10 -6 ) = 3.086 x 10 13 km = 3.26 light years 1 light-year is the distance light will travel in one year 1 light-year = (2.998 x 10 8 m/s)(86400 s/d)(365 d/y) = 9.46 x 10 12 km = 9.46 x 10 15 m A LIGHTYEAR IS A DISTANCE, NOT A TIME! Slide 16 February 18, 2003Lynn Cominsky - Cosmology A35015 Parallax movie Slide 17 February 18, 2003Lynn Cominsky - Cosmology A35016 The Nearest Stars Distance to Alpha Centauri system is ~4 x 10 11 km or ~4.2 light years or ~1.3 parsecs Parallax is a bit less than 1 arcsecond Slide 18 February 18, 2003Lynn Cominsky - Cosmology A35017 The Solar Neighborhood Some stars within about 2 x 10 14 km (~ 20 light years) Slide 19 February 18, 2003Lynn Cominsky - Cosmology A35018 430 772 242 721 817 1342 915 343 89 Case Study 4: The Absolute Lightness of Being Stars are far, har har har Slide 20 February 18, 2003Lynn Cominsky - Cosmology A35019 Absolute vs. Apparent magnitude Apparent magnitude - How bright does the star appear (from the Earth)? Uses symbol m Absolute magnitude - the apparent magnitude of a star if it were located at 10 pc. Uses symbol M Absolute and apparent magnitude are related to the true distance D to the star by: m M = 5 log (D/10 pc) = 5 log (D/pc) 5 OR D = 10 pc * 10 ((m-M)/5) Magnitudes seem backwards the bigger the number, the fainter the star. Case Study 4: The Absolute Lightness of Being Slide 21 February 18, 2003Lynn Cominsky - Cosmology A35020 Ogden now has distances, and can measure temperatures. With distance, can get absolute magnitude. Plots one versus the other. Case Study 4: The Absolute Lightness of Being Slide 22 February 18, 2003Lynn Cominsky - Cosmology A35021 Orion Heat B8I M2I B2III B0I K5III A5V Slide 23 February 18, 2003Lynn Cominsky - Cosmology A35022 Classifying Stars Hertzsprung-Russell diagram Slide 24 February 18, 2003Lynn Cominsky - Cosmology A35023 Main Sequence Stars spend most of their lives on the Main Sequence How do they get there? What happens when they leave? Slide 25 February 18, 2003Lynn Cominsky - Cosmology A35024 Stellar Spectral types OBAFGKMLT (Oh, Be A Fine Guy/Girl, Kiss My Lips Thoroughly) Describe spectral features of stars Linked to temperature (not necessarily mass!) Once understood, leads to stellar life cycles Slide 26 February 18, 2003Lynn Cominsky - Cosmology A35025 Properties of Stars Temperature (degrees K) - color of star light. All stars with the same blackbody temperature are the same color. Specific spectral lines appear for each temperature range classification. Astronomers name temperature ranges in decreasing order as: Surface gravity - measured from the shapes of the stellar absorption lines. Distinguishes classes of stars: supergiants, giants, main sequence stars and white dwarfs. O B A F G K M Slide 27 February 18, 2003Lynn Cominsky - Cosmology A35026 Classes of Stars Bigger stars are brighter than smaller stars because they have more surface area Hotter stars make more light per square meter. So, for a given size, hotter stars are brighter than cooler stars. White dwarfs - small and can be very hot (Class VII) Main sequence stars - range from hotter and larger to smaller and cooler (Class V) Giants - rather large and cool (Class III) Supergiants - cool and very large (Class I) Slide 28 February 18, 2003Lynn Cominsky - Cosmology A35027 Life Cycles of Stars Slide 29 February 18, 2003Lynn Cominsky - Cosmology A35028 Molecular clouds and protostars Giant molecular clouds are very cold, thin and wispy they stretch out over tens of light years at temperatures from 10-100K, with a warmer core They are 1000s of time more dense than the local interstellar medium, and collapse further under their own gravity to form protostars at their cores Orion in mm radio (BIMA) Simulation with narration by Jack Welch (UCB) Slide 30 February 18, 2003Lynn Cominsky - Cosmology A35029 Logans Run Introduce Logans Protostar game Slide 31 February 18, 2003Lynn Cominsky - Cosmology A35030 Protostars Orion nebula/Trapezium stars (in the sword) About 1500 light years away HST / 2.5 light years Chandra/10 light years Slide 32 February 18, 2003Lynn Cominsky - Cosmology A35031 Disks around stars There is much evidence of disks with gaps (presumably caused by planets) around bright, nearby stars, such as Beta Pictoris, or HD141569 (shown here) Slide 33 February 18, 2003Lynn Cominsky - Cosmology A35032 Stellar nurseries Pillars of dense gas Newly born stars may emerge at the ends of the pillars About 7000 light years away HST/Eagle Nebula in M16 Slide 34 February 18, 2003Lynn Cominsky - Cosmology A35033 Pleiades Star Cluster A star cluster has a group of stars which are all located at approximately the same distance The stars in the Pleiades were all formed at about the same time, from a single cloud of dust and gas Roughly 10 8 years old D = 116 pc Slide 35 February 18, 2003Lynn Cominsky - Cosmology A35034 HR Diagram again as a reminder Hertzsprung-Russell diagram Slide 36 February 18, 2003Lynn Cominsky - Cosmology A35035 Main Sequence Stars Stars spend most of their lives on the main sequence where they burn hydrogen in nuclear reactions in their cores Burning rate is higher for more massive stars - hence their lifetimes on the main sequence are much shorter and they are rather rare Red dwarf stars are the most common as they burn hydrogen slowly and live the longest Often called dwarfs (but not the same as White Dwarfs) because they are smaller than giants or supergiants Our sun is considered a G2V star. It has been on the main sequence for about 4.5 billion years, with another ~5 billion to go Slide 37 February 18, 2003Lynn Cominsky - Cosmology A35036 Nuclear Fusion ! At 15 million degrees Celsius in the center of the star, fusion ignites ! 4 ( 1 H) --> 4 He + 2 e + + 2 neutrinos + energy Where does the energy come from ? Mass of four 1 H > Mass of one 4 He E = mc 2 Slide 38 February 18, 2003Lynn Cominsky - Cosmology A35037 How much Energy 4 ( 1 H) --> 4 He + 2 e + + 2 neutrinos + energy Energy released = 25 MeV = 4 x 10 -12 Joules = 1 x 10 -15 Calories But the sun does this 10 38 times a second ! Sun has 10 56 H atoms to burn ! Slide 39 February 18, 2003Lynn Cominsky - Cosmology A35038 A Balancing Act Energy released from nuclear fusion counter-acts inward force of gravity. Throughout its life, these two forces determine the stages of a stars life. Slide 40 February 18, 2003Lynn Cominsky - Cosmology A35039 A Red Giant You Know Slide 41 February 18, 2003Lynn Cominsky - Cosmology A35040 The Beginning of the End: Red Giants After Hydrogen is exhausted in core... Energy released from nuclear fusion counter-acts inward force of gravity. Core collapses, Kinetic energy of collapse converted into heat. This heat expands the outer layers. Meanwhile, as core collapses, Increasing Temperature and Pressure... Slide 42 February 18, 2003Lynn Cominsky - Cosmology A35041 More Fusion ! At 100 million degrees Celsius, Helium fuses: 3 ( 4 He) --> 12 C + energy (Be produced at an intermediate step) (Only 7.3 MeV produced) Energy sustains the expanded outer layers of the Red Giant Slide 43 February 18, 2003Lynn Cominsky - Cosmology A35042 Stellar evolution made simple Stars like the Sun go gentle into that good night More massive stars rage, rage against the dying of the light Puff! Bang! BANG! Slide 44 February 18, 2003Lynn Cominsky - Cosmology A35043 How stars die Stars that are below about 8 M o form red giants at the end of their lives on the main sequence Red giants evolve into white dwarfs, often accompanied by planetary nebulae More massive stars form red supergiants Red supergiants undergo supernova explosions, often leaving behind a stellar core which is a neutron star, or perhaps a black hole (more in later lectures about these topics) Slide 45 February 18, 2003Lynn Cominsky - Cosmology A35044 Red Giants and Supergiants Hydrogen burns in outer shell around the core Heavier elements burn in inner shells Slide 46 February 18, 2003Lynn Cominsky - Cosmology A35045 White dwarf stars Red giants (but not supergiants) turn into white dwarf stars as they run out of fuel White dwarf mass must be less than 1.4 M o White dwarfs do not collapse because of quantum mechanical pressure from degenerate electrons White dwarf radius is about the same as the Earth A teaspoon of a white dwarf would weigh 10 tons Some white dwarfs have magnetic fields as high as 10 9 Gauss White dwarfs eventually radiate away all their heat and end up as black dwarfs in billions of years Slide 47 February 18, 2003Lynn Cominsky - Cosmology A35046 Planetary nebulae Planetary nebulae are not the origin of planets Outer ejected shells of red giant illuminated by a white dwarf formed from the giants burnt-out core Not always formed HST/WFPC2 Eskimo nebula 5000 light years Slide 48 February 18, 2003Lynn Cominsky - Cosmology A35047 Fate of high mass stars After Helium exhausted, core collapses again until it becomes hot enough to fuse Carbon into Magnesium or Oxygen. 12 C + 12 C --> 24 Mg OR 12 C + 4 H --> 16 O Through a combination of processes, successively heavier elements are formed and burned. Slide 49 February 18, 2003Lynn Cominsky - Cosmology A35048 Heavy Elements from Large Stars Large stars also fuse Hydrogen into Helium, and Helium into Carbon. But their larger masses lead to higher temperatures, which allow fusion of Carbon into Magnesium, etc. Slide 50 February 18, 2003Lynn Cominsky - Cosmology A35049 Periodic Table 16 O + 16 O 32 S + energy 4 He + 16 O 20 Ne + energy Light Elements Heavy Elements 4 ( 1 H) 4 He + energy 3( 4 He) 12 C + energy 12 C + 12 C 24 Mg + energy 4 He + 12 C 16 O + energy 28 Si + 7( 4 He) 56 Ni + energy 56 FeC-N-O Cycle Slide 51 February 18, 2003Lynn Cominsky - Cosmology A35050 The End of the Line for Massive Stars Massive stars burn a succession of elements. Iron is the most stable element and cannot be fused further. Instead of releasing energy, it uses energy. Slide 52 February 18, 2003Lynn Cominsky - Cosmology A35051 Supernova ! Slide 53 February 18, 2003Lynn Cominsky - Cosmology A35052 Supernova Remnants: SN1987A ab cd a) Optical - Feb 2000 Illuminating material ejected from the star thousands of years before the SN b) Radio - Sep 1999 c) X-ray - Oct 1999 d) X-ray - Jan 2000 The shock wave from the SN heating the gas Slide 54 February 18, 2003Lynn Cominsky - Cosmology A35053 Supernova Remnants: Cas A OpticalX-ray Slide 55 February 18, 2003Lynn Cominsky - Cosmology A35054 Elements from Supernovae All X-ray Energies Silicon Calcium Iron Slide 56 February 18, 2003Lynn Cominsky - Cosmology A35055 Composition of the Universe Actually, this is just the solar system. Composition varies from place to place in universe, and between different objects. Slide 57 February 18, 2003Lynn Cominsky - Cosmology A35056 Whats Out There? A classroom activity that demonstrates the different elemental compositions of different objects in the universe. Demonstrates how we estimate the abundances. (Developed by Stacie Kreitman, Falls Church, VA) Slide 58 February 18, 2003Lynn Cominsky - Cosmology A35057 Top 10 Elements in the Human Body Element by # atoms 10.Magnesium (Mg)0.03% 9.Chlorine (Cl)0.04% 8.Sodium (Na)0.06% 7.Sulfur (S)0.06% 6.Phosphorous (P)0.20% 5.Calcium (Ca)0.24% 4. Nitrogen (N) 1.48% 3.Carbon (C) 9.99% 2.Oxygen (O) 26.33% 1.Hydrogen (H) 61.56% Slide 59 February 18, 2003Lynn Cominsky - Cosmology A35058 Spectral Analysis We cant always get a sample of a piece of the Universe. So we depend on light ! Slide 60 February 18, 2003Lynn Cominsky - Cosmology A35059 Spectral Analysis Each element has a unique spectral signature: Determined by arrangement of electrons. Lines of emission or absorption arise from re-arrangement of electrons into different energy levels. Hydrogen Slide 61 February 18, 2003Lynn Cominsky - Cosmology A35060 Nickel-odeon Classroom Activity Spread a rainbow of color across a piano keyboard (Developed by Shirley Burris, Nova Scotia) Then, play an element Hydrogen Slide 62 February 18, 2003Lynn Cominsky - Cosmology A35061 More Musical Elements Now play another element Helium Carbon And Another Slide 63 February 18, 2003Lynn Cominsky - Cosmology A35062 Getting a Handle on Water Oxygen All together now... Hydrogen Water Slide 64 February 18, 2003Lynn Cominsky - Cosmology A35063 Supernovae Supergiant stars become (Type II) supernovae at the end of nuclear shell burning Iron core often remains as outer layers are expelled Neutrinos and heavy elements released Core continues to collapse Chandra X-ray image of Eta Carinae, a potential supernova Slide 65 February 18, 2003Lynn Cominsky - Cosmology A35064 Making a Neutron Star Slide 66 February 18, 2003Lynn Cominsky - Cosmology A35065 Neutron Stars Neutron stars are formed from collapsed iron cores All neutron stars that have been measured have around 1.4 M o (Chandrasekhar mass) Neutron stars are supported by pressure from degenerate neutrons, formed from collapsed electrons and protons A teaspoonful of neutron star would weigh 1 billion tons Neutron stars with very strong magnetic fields - around 10 12-13 Gauss - are usually pulsars due to offset magnetic poles Slide 67 February 18, 2003Lynn Cominsky - Cosmology A35066 Neutron Stars: Dense cinders Mass: ~1.4 solar masses Radius: ~10 kilometers Density: 10 14-15 g/cm 3 Magnetic field: 10 8-14 gauss Spin rate: from 1000Hz to 0.08 Hz Slide 68 February 18, 2003Lynn Cominsky - Cosmology A35067 Crab nebula Observed by Chinese astronomers in 1054 AD Age determined by tracing back exploding filaments Crab pulsar emits 30 pulses per second at all wavelengths from radio to TeV movie Slide 69 February 18, 2003Lynn Cominsky - Cosmology A35068 Crab nebula Radio/VLA Infrared/Keck Slide 70 February 18, 2003Lynn Cominsky - Cosmology A35069 Crab nebula Optical/HST WFPC2 Optical/Palomar Slide 71 February 18, 2003Lynn Cominsky - Cosmology A35070 Crab nebula and pulsar X-ray/Chandra Slide 72 February 18, 2003Lynn Cominsky - Cosmology A35071 Cas A ~320 years old 10 light years across 50 million degree shell Radio/VLA X-ray/Chandra neutron star Slide 73 February 18, 2003Lynn Cominsky - Cosmology A35072 Not all explosions are created equal Slide 74 February 18, 2003Lynn Cominsky - Cosmology A35073 Classifying Bursts In this activity, you will be given twenty cards showing different types of bursts Pay attention to the lightcurves, optical counterparts and other properties of the bursts given on the reverse of the cards How many different types of bursts are there? Sort the bursts into different classes Fill out the accompanying worksheet to explain the reasoning behind your classification scheme Slide 75 February 18, 2003Lynn Cominsky - Cosmology A35074 What makes Gamma-ray Bursts? X-ray Bursts Properties Thermonuclear Flash Model Soft Gamma Repeaters Properties Magnetar model Gamma-ray Bursts Properties Models Afterglows Future Mission Studies Slide 76 February 18, 2003Lynn Cominsky - Cosmology A35075 X-ray Bursts Thermonuclear flashes on Neutron Star surface hydrogen or helium fusion Accreting material burns in shells, unstable burning leads to thermonuclear runaway Bursts repeat every few hours to days Bursts are never seen from black hole binaries (no surface for unstable nuclear burning) or from (almost all) pulsars (magnetic field quenches thermonuclear runaway) Slide 77 February 18, 2003Lynn Cominsky - Cosmology A35076 X-ray Burst Sources Locations in Galactic Coordinates burstersnon-burstersGlobular Clusters Most bursters are located in globular clusters or near the Galactic center They are therefore relatively older systems Slide 78 February 18, 2003Lynn Cominsky - Cosmology A35077 X-ray Burst Source Properties Weaker magnetic dipole: B~10 8 G NS spin period seen in bursts ~0.003 sec. Orbital periods : 0.19 - 398 h from X-ray dips & eclipses and/or optical modulation > 15 well known bursting systems Low mass companions L x = 10 36 - 10 38 erg/s Neutron Stars in binary systems Slide 79 February 18, 2003Lynn Cominsky - Cosmology A35078 X-ray Emission X-ray emission from accretion can be modulated by magnetic fields, unstable burning and spin Modulation due to spin of neutron star can sometimes be seen within the burst Slide 80 February 18, 2003Lynn Cominsky - Cosmology A35079 Soft Gamma Repeaters There are four of these objects known to date One is in the LMC, the other 3 are in the Milky Way LMC SGR 1627-41 Slide 81 February 18, 2003Lynn Cominsky - Cosmology A35080 Soft Gamma Repeater Properties Superstrong magnetic dipole: B~10 14-15 G NS spin period seen in bursts ~5-10 sec, shows evidence of rapid spin down No orbital periods not in binaries! 4 well studied systems + several other candidate systems Several SGRs are located in or near SNRs Soft gamma ray bursts are from magnetic reconnection/flaring like giant solar flares L x = 10 42 - 10 43 erg/s at peak of bursts Young Neutron Stars near SNRs Slide 82 February 18, 2003Lynn Cominsky - Cosmology A35081 SGR 1900+14 Strong burst showing ~5 sec pulses Change in 5 s spin rate leads to measure of magnetic field Source is a magnetar! Slide 83 February 18, 2003Lynn Cominsky - Cosmology A35082 SGR burst affects Earth On the night of August 27, 1998 Earth's upper atmosphere was bathed briefly by an invisible burst of gamma- and X-ray radiation. This pulse - the most powerful to strike Earth from beyond the solar system ever detected - had a significant effect on Earth's upper atmosphere, report Stanford researchers. It is the first time that a significant change in Earth's environment has been traced to energy from a distant star. (from the NASA press release) Slide 84 February 18, 2003Lynn Cominsky - Cosmology A35083 Gamma Ray Burst Properties Unknown magnetic field No repeatable periods seen in bursts No orbital periods seen not in binaries Thousands of bursts seen to date no repetitions from same location Isotropic distribution Afterglows have detectable redshifts which indicate GRBs are at cosmological distances (i.e., far outside our galaxy) L = 10 52 - 10 53 erg/s at peak of bursts A cataclysmic event of unknown origin Slide 85 February 18, 2003Lynn Cominsky - Cosmology A35084 The first Gamma-ray Burst Discovered in 1967 while looking for nuclear test explosions - a 30+ year old mystery! Vela satellite Slide 86 February 18, 2003Lynn Cominsky - Cosmology A35085 Compton Gamma Ray Observatory Eight instruments on corners of spacecraft NaI scintillators BATSE Slide 87 February 18, 2003Lynn Cominsky - Cosmology A35086 The GRB Gallery When youve seen one gamma-ray burst, youve seen. one gamma-ray burst!! Slide 88 February 18, 2003Lynn Cominsky - Cosmology A35087 GRBs the Second: Angling for GRBs Using data from several satellites in the solar system, you will use a light ruler to figure out the direction to a gamma- ray burst This is similar to the way that the Interplanetary Network (IPN) really works See http://ssl.berkeley.edu/ipn3/ Slide 89 February 18, 2003Lynn Cominsky - Cosmology A35088 GRB the Third: The Plots Thicken Introduce it Slide 90 February 18, 2003Lynn Cominsky - Cosmology A35089 CGRO/BATSE Gamma-ray Burst Sky Once a day, somewhere in the Universe Slide 91 February 18, 2003Lynn Cominsky - Cosmology A35090 Near or Far? Isotropic distribution implications: Silly or not, the only way to be sure was to find the afterglow. Very close: within a few parsecs of the Sun Very far: huge, cosmological distances Sort of close: out in the halo of the Milky Way Why no faint bursts? What could produce such a vast amount of energy? A comet hitting a neutron star fits the bill Slide 92 February 18, 2003Lynn Cominsky - Cosmology A35091 Breakthrough! In 1997, BeppoSAX detects X-rays from a GRB afterglow for the first time, 8 hours after burst Slide 93 February 18, 2003Lynn Cominsky - Cosmology A35092 The View From Hubble/STIS 7 months later Slide 94 February 18, 2003Lynn Cominsky - Cosmology A35093 On a clear night, you really can see forever! 990123 reached 9 th magnitude for a few moments! First optical GRB afterglow detected simultaneously Slide 95 February 18, 2003Lynn Cominsky - Cosmology A35094 GRB the Fourth: Beam me Up Introduce the activity Problem: with known distance, what could give off that much energy? Maybe nothing! Need beaming. Slide 96 February 18, 2003Lynn Cominsky - Cosmology A35095 The Supernova Connection GRB011121 Afterglow faded like supernova Data showed presence of gas like a stellar wind Indicates some sort of supernova and not a NS/NS merger Slide 97 February 18, 2003Lynn Cominsky - Cosmology A35096 Hypernova A billion trillion times the power from the Sun The end of the life of a star that had 100 times the mass of our Sun movie Slide 98 February 18, 2003Lynn Cominsky - Cosmology A35097 Iron lines in GRB 991216 Chandra observations show link to hypernova model when hot iron-filled gas is detected from GRB 991216 Iron is a signature of a supernova, as it is made in the cores of stars, and released in supernova explosions Slide 99 February 18, 2003Lynn Cominsky - Cosmology A35098 Catastrophic Mergers Death spiral of 2 neutron stars or black holes Slide 100 February 18, 2003Lynn Cominsky - Cosmology A35099 Which model is right? The data seem to indicate two kinds of GRBs Those with burst durations less than 2 seconds Those with burst durations more than 2 seconds Short bursts have no detectable afterglows so far as predicted by the NS/NS merger model Long bursts are sometimes associated with supernovae, and all the afterglows seen so far as predicted by the hypernova merger model Slide 101 February 18, 2003Lynn Cominsky - Cosmology A350100 Gamma-ray Bursts Either way you look at it hypernova or merger model GRBs signal the birth of a black hole! Slide 102 February 18, 2003Lynn Cominsky - Cosmology A350101 Gamma-ray Bursts Or maybe the death of life on Earth? No, gamma- ray bursts did not kill the dinosaurs! Slide 103 February 18, 2003Lynn Cominsky - Cosmology A350102 How to study Gamma rays? Absorbed by the Earths atmosphere Use rockets, balloons or satellites Cant image or focus gamma rays Special detectors: crystals, silicon-strips GLAST balloon test Slide 104 February 18, 2003Lynn Cominsky - Cosmology A350103 HETE-2 Launched on 10/9/2000 Operational and finding about 2 bursts per month Slide 105 February 18, 2003Lynn Cominsky - Cosmology A350104 Swift Mission Burst Alert Telescope (BAT) Ultraviolet/Optical Telescope (UVOT) X-ray Telescope (XRT) To be launched in 2003 Slide 106 February 18, 2003Lynn Cominsky - Cosmology A350105 Swift Mission Will study GRBs with swift response Survey of hard X-ray sky To be launched in 2003 Nominal 3-year lifetime Will see ~150 GRBs per year Slide 107 February 18, 2003Lynn Cominsky - Cosmology A350106 Gamma-ray Large Area Space Telescope GLAST Burst Monitor (GBM) Large Area Telescope (LAT) Slide 108 February 18, 2003Lynn Cominsky - Cosmology A350107 GRBs and Cosmology GRBs can be used as standard candles, similar to Type 1a supernovae However, the supernovae are only seen out to z=0.7 (and one at z=1.7), whereas GRBs are seen to z=4.5, and may someday be seen to z=10 Schaefer (2002) has constructed a Hubble diagram for GRBs, using the cosmological parameters from supernova data. When more burst redshifts become available (e.g., from Swift), the parameters can be determined independently