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Astronomy 350 Cosmology Professor Lynn Cominsky Department of Physics and Astronomy Offices: Darwin 329A and NASA EPO (707) 664-2655 Best way to reach me: [email protected] March 11, 2003 Lynn Cominsky - Cosmology A350 1 Group 6 Justin Beck Tiffany Henning Pamela Riek Ryan Silva March 11, 2003 Lynn Cominsky - Cosmology A350 2 Stellar evolution made simple Puff! Bang! BANG! Stars like the Sun go gentle into that good night More massive stars rage, rage against the dying of the light March 11, 2003 Lynn Cominsky - Cosmology A350 3 Exploding Stars Supernova 1987A in Large Magellanic Cloud HST/WFPC2 At the end of a star’s life, if it is large enough, it will end with a bang (and not a whimper!) March 11, 2003 Lynn Cominsky - Cosmology A350 4 Supernova Remnants Vela Region CGRO/Comptel Radioactive decay of chemical elements created by the supernova explosion March 11, 2003 Lynn Cominsky - Cosmology A350 5 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 March 11, 2003 Chandra X-ray image of Eta Carinae, a potential supernova Lynn Cominsky - Cosmology A350 6 Making a Neutron Star March 11, 2003 Lynn Cominsky - Cosmology A350 7 Three views of a Supernova Lightcurve Image March 11, 2003 Spectrum Lynn Cominsky - Cosmology A350 8 Crab nebula movie 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 March 11, 2003 Lynn Cominsky - Cosmology A350 9 Crab nebula Radio/VLA March 11, 2003 Infrared/Keck Lynn Cominsky - Cosmology A350 10 Crab nebula Optical/Palomar March 11, 2003 Optical/HST WFPC2 Lynn Cominsky - Cosmology A350 11 Crab nebula and pulsar X-ray/Chandra March 11, 2003 Lynn Cominsky - Cosmology A350 12 Cas A ~320 years old 10 light years across 50 million degree shell neutron star Radio/VLA March 11, 2003 Lynn Cominsky - Cosmology A350 X-ray/Chandra 13 Neutron Stars Neutron stars are formed from collapsed iron cores All neutron stars that have been measured have around 1.4 Mo (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 1012-13 Gauss - are usually pulsars due to offset magnetic poles March 11, 2003 Lynn Cominsky - Cosmology A350 14 Neutron Stars: Dense cinders Mass: ~1.4 solar masses Radius: ~10 kilometers Density: 1014-15 g/cm3 Magnetic field: 108-14 gauss Spin rate: from 1000Hz to 0.08 Hz March 11, 2003 Lynn Cominsky - Cosmology A350 15 Distances to Supernovae Supernova 1987A in LMC Brightest SN in modern times, occurred at t0 Measure angular diameter of ring, q Measure times when top and bottom of ring light up, t2 and t1 Ring radius is given by R = c(t1-t0 + t2-t0)/2 Distance = R / q March 11, 2003 Lynn Cominsky - Cosmology A350 D = 47 kpc 16 Distances to Supernovae Type Ia supernovae are “standard candles” Occur in a binary system in which a white dwarf star accretes beyond the 1.4 Mo Chandrasekhar limit and collapses and explodes Decay time of light curve is correlated to absolute luminosity Luminosity comes from the radioactive decay of Cobalt and Nickel into Iron Some Type Ia supernovae are in galaxies with Cepheid variables Good to 20% as a distance measure March 11, 2003 Lynn Cominsky - Cosmology A350 17 Standard Candles If you have two light sources that you know are the same brightness The apparent brightness of the distant source will allow you to calculate its distance, compared to the nearby source This is because the brightness decreases like 1/(distance)2 March 11, 2003 Lynn Cominsky - Cosmology A350 movie 18 Cosmological parameters W = density of the universe / critical density W< 1 hyperbolic geometry W = 1 flat or Euclidean W > 1 spherical geometry March 11, 2003 Lynn Cominsky - Cosmology A350 19 Cosmological parameters In order to find the density of the Universe, you must measure its total amount of matter and energy, including: All the matter we see All the dark matter that we don’t see but we feel All the energy from starlight, background radiation, etc. The part of the total density/critical density that could be due to matter and/or energy = WM Current measurements : WM < 0.3 March 11, 2003 Lynn Cominsky - Cosmology A350 20 Supernovae & Cosmology WM = matter WL = cosmological constant Redshift March 11, 2003 0 0.2 0.4 0.6 Lynn Cominsky - Cosmology A350 0.8 1 21 Einstein meets Hubble WM = 8 p G r 3 Ho 2 WL = L 3 Ho2 W(total) = WM + WL Perlmutter et al. 40 supernovae March 11, 2003 Lynn Cominsky - Cosmology A350 22 Accelerating Universe Results from Perlmutter et al. (and also by another group from Harvard, Kirshner et al.) strongly suggest that if WM = 0.3 : WL = 0.7 There is some type of dark energy which is causing the expansion of the Universe to accelerate Other results indicate that Wtotal = 1 This will be discussed later at much greater length March 11, 2003 Lynn Cominsky - Cosmology A350 23 Distributions If sources are located randomly in space, the distribution is called isotropic If the sources are concentrated in a certain region or along the galactic plane, the distribution is anisotropic March 11, 2003 Lynn Cominsky - Cosmology A350 24 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 March 11, 2003 Lynn Cominsky - Cosmology A350 25 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 March 11, 2003 Lynn Cominsky - Cosmology A350 26 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) March 11, 2003 Lynn Cominsky - Cosmology A350 27 X-ray Burst Sources Locations in Galactic Coordinates bursters non-bursters Globular Clusters • Most bursters are located in globular clusters or near the Galactic center • They are therefore relatively older systems March 11, 2003 Lynn Cominsky - Cosmology A350 28 X-ray Burst Source Properties Neutron Stars in binary systems Weaker magnetic dipole: B~108 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 Lx = 1036 - 1038 erg/s March 11, 2003 Lynn Cominsky - Cosmology A350 29 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 March 11, 2003 Lynn Cominsky - Cosmology A350 30 X-ray Burst Sources Burst spectra are thermal black-body L(t) = 4 p R2 s T(t)4 Temperature Radius Expansion c2 March 11, 2003 Lynn Cominsky - Cosmology A350 Cominsky PhD 1981 31 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 SGR 1627-41 LMC March 11, 2003 Lynn Cominsky - Cosmology A350 32 Soft Gamma Repeater Properties Young Neutron Stars near SNRs Superstrong magnetic dipole: B~1014-15 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 Lx = 1042 - 1043 erg/s at peak of bursts March 11, 2003 Lynn Cominsky - Cosmology A350 33 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! March 11, 2003 Lynn Cominsky - Cosmology A350 34 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) March 11, 2003 Lynn Cominsky - Cosmology A350 35 Gamma Ray Burst Properties A cataclysmic event of unknown origin 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) Lg = 1052 - 1053 erg/s at peak of bursts March 11, 2003 Lynn Cominsky - Cosmology A350 36 The first Gamma-ray Burst Vela satellite Discovered in 1967 while looking for nuclear test explosions - a 30+ year old mystery! March 11, 2003 Lynn Cominsky - Cosmology A350 37 Compton Gamma Ray Observatory BATSE • Eight instruments on corners of spacecraft • NaI scintillators March 11, 2003 Lynn Cominsky - Cosmology A350 38 CGRO/BATSE Gamma-ray Burst Sky Once a day, somewhere in the Universe March 11, 2003 Lynn Cominsky - Cosmology A350 39 The GRB Gallery When you’ve seen one gamma-ray burst, you’ve seen…. one gamma-ray burst!! March 11, 2003 Lynn Cominsky - Cosmology A350 40 Near or Far? Isotropic distribution implications: Very close: within a few parsecs of the Sun Why no faint bursts? Very far: huge, cosmological distances What could produce such a vast amount of energy? Sort of close: out in the halo of the Milky Way A comet hitting a neutron star fits the bill Silly or not, the only way to be sure was to find the afterglow. March 11, 2003 Lynn Cominsky - Cosmology A350 41 Breakthrough! In 1997, BeppoSAX detects X-rays from a GRB afterglow for the first time, 8 hours after burst March 11, 2003 Lynn Cominsky - Cosmology A350 42 The View From Hubble/STIS 7 months later March 11, 2003 Lynn Cominsky - Cosmology A350 43 On a clear night, you really can see forever! 990123 reached 9th magnitude for a few moments! First optical GRB afterglow detected simultaneously March 11, 2003 Lynn Cominsky - Cosmology A350 44 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 March 11, 2003 Lynn Cominsky - Cosmology A350 45 Hypernova movie 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 March 11, 2003 Lynn Cominsky - Cosmology A350 46 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 March 11, 2003 Lynn Cominsky - Cosmology A350 47 Catastrophic Mergers Death spiral of 2 neutron stars or black holes March 11, 2003 Lynn Cominsky - Cosmology A350 48 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 March 11, 2003 Lynn Cominsky - Cosmology A350 49 Gamma-ray Bursts Either way you look at it – hypernova or merger model GRBs signal the birth of a black hole! March 11, 2003 Lynn Cominsky - Cosmology A350 50 Gamma-ray Bursts Or maybe the death of life on Earth? No, gammaray bursts did not kill the dinosaurs! March 11, 2003 Lynn Cominsky - Cosmology A350 51 How to study Gamma rays? Absorbed by the Earth’s atmosphere Use rockets, balloons or satellites Can’t image or focus gamma rays Special detectors: crystals, silicon-strips March 11, 2003 Lynn Cominsky - Cosmology A350 GLAST balloon test 52 HETE-2 Launched on 10/9/2000 Operational and finding about 2 bursts per month March 11, 2003 Lynn Cominsky - Cosmology A350 53 Swift Mission To be launched in 2003 Burst Alert Telescope (BAT) Ultraviolet/Optical Telescope (UVOT) X-ray Telescope (XRT) March 11, 2003 Lynn Cominsky - Cosmology A350 54 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 March 11, 2003 Lynn Cominsky - Cosmology A350 55 Gamma-ray Large Area Space Telescope GLAST Burst Monitor (GBM) Large Area Telescope (LAT) March 11, 2003 Lynn Cominsky - Cosmology A350 56 GLAST Mission First space-based collaboration between astrophysics and particle physics communities Launch expected in 2006 Expected duration 5-10 years Over 3000 gamma-ray sources will be seen March 11, 2003 Lynn Cominsky - Cosmology A350 57 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 March 11, 2003 Lynn Cominsky - Cosmology A350 58 The Great Interplanetary GRB Hunt Using data from several satellites in the solar system, you will use a “light ruler” to figure out the direction to a gammaray burst This is similar to the way that the Interplanetary Network (IPN) really works See http://ssl.berkeley.edu/ipn3/ March 11, 2003 Lynn Cominsky - Cosmology A350 59 Web Resources : GLAST E/PO web site http://glast.sonoma.edu Swift E/PO web site http://swift.sonoma.edu Imagine the Universe! http://imagine.gsfc.nasa.gov Science at NASA’s Marshall Space Flight Center http://science.nasa.gov Supernova Cosmology Project http://panisse.lbl.gov/ Ned Wright’s ABCs of Distance http://www.astro.ucla.edu/~wright/distance.htm March 11, 2003 Lynn Cominsky - Cosmology A350 60 Web Resources Robert Duncan’s magnetar page http://solomon.as.utexas.edu/~duncan/magnetar.html Chandra observatory http://chandra.harvard.edu Jochen Greiner’s Gamma-ray bursts and SGR Summaries http://www.mpe.mpg.de/~jcg HETE-2 mission http://space.mit.edu/HETE/ Compton Gamma Ray Observatory http://cossc.gsfc.nasa.gov/ March 11, 2003 Lynn Cominsky - Cosmology A350 61