March 11, 2003Lynn Cominsky - Cosmology A3501 Professor Lynn Cominsky Department of Physics and Astronomy Offices: Darwin 329A and NASA EPO (707) Best way to reach me: Astronomy 350 Cosmology

March 11, 2003Lynn Cominsky - Cosmology A3502 Group 6  Justin Beck  Tiffany Henning  Pamela Riek  Ryan Silva

March 11, 2003Lynn Cominsky - Cosmology A3503 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!

March 11, 2003Lynn Cominsky - Cosmology A3504 Exploding Stars  At the end of a star’s life, if it is large enough, it will end with a bang (and not a whimper!) Supernova 1987A in Large Magellanic Cloud HST/WFPC2

March 11, 2003Lynn Cominsky - Cosmology A3505 Supernova Remnants  Radioactive decay of chemical elements created by the supernova explosion Vela Region CGRO/Comptel

March 11, 2003Lynn Cominsky - Cosmology A3506 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

March 11, 2003Lynn Cominsky - Cosmology A3507 Making a Neutron Star

March 11, 2003Lynn Cominsky - Cosmology A3508 Three views of a Supernova Lightcurve Spectrum Image

March 11, 2003Lynn Cominsky - Cosmology A3509 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

March 11, 2003Lynn Cominsky - Cosmology A35010 Crab nebula Radio/VLA Infrared/Keck

March 11, 2003Lynn Cominsky - Cosmology A35011 Crab nebula Optical/HST WFPC2 Optical/Palomar

March 11, 2003Lynn Cominsky - Cosmology A35012 Crab nebula and pulsar X-ray/Chandra

March 11, 2003Lynn Cominsky - Cosmology A35013 Cas A  ~320 years old  10 light years across  50 million degree shell Radio/VLA X-ray/Chandra neutron star

March 11, 2003Lynn Cominsky - Cosmology A35014 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 Gauss - are usually pulsars due to offset magnetic poles

March 11, 2003Lynn Cominsky - Cosmology A35015 Neutron Stars: Dense cinders Mass: ~1.4 solar masses Radius: ~10 kilometers Density: g/cm 3 Magnetic field: gauss Spin rate: from 1000Hz to 0.08 Hz

March 11, 2003Lynn Cominsky - Cosmology A35016 Distances to Supernovae  Brightest SN in modern times, occurred at t 0  Measure angular diameter of ring,   Measure times when top and bottom of ring light up, t 2 and t 1  Ring radius is given by R = c(t 1 -t 0 + t 2 -t 0 )/2  Distance = R /  Supernova 1987A in LMC D = 47 kpc

March 11, 2003Lynn Cominsky - Cosmology A35017 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 M o 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, 2003Lynn Cominsky - Cosmology A35018 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 movie

March 11, 2003Lynn Cominsky - Cosmology A35019 Cosmological parameters  = density of the universe / critical density  hyperbolic geometry  flat or Euclidean  spherical geometry

March 11, 2003Lynn Cominsky - Cosmology A35020 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 =  M  Current measurements :  M  < 0.3

March 11, 2003Lynn Cominsky - Cosmology A Supernovae & Cosmology  M = matter   = cosmological constant Redshift

March 11, 2003Lynn Cominsky - Cosmology A35022  M = 8  G  3 H o 2    3 H o 2  (total)  M +   Einstein meets Hubble Perlmutter et al. 40 supernovae

March 11, 2003Lynn Cominsky - Cosmology A35023 Accelerating Universe  Results from Perlmutter et al. (and also by another group from Harvard, Kirshner et al.) strongly suggest that if   = 0.3 :    There is some type of dark energy which is causing the expansion of the Universe to accelerate  Other results indicate that  total = 1  This will be discussed later at much greater length

March 11, 2003Lynn Cominsky - Cosmology A35024 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, 2003Lynn Cominsky - Cosmology A35025 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, 2003Lynn Cominsky - Cosmology A35026 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, 2003Lynn Cominsky - Cosmology A35027 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, 2003Lynn Cominsky - Cosmology A35028 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

March 11, 2003Lynn Cominsky - Cosmology A35029 X-ray Burst Source Properties Weaker magnetic dipole: B~10 8 G NS spin period seen in bursts ~0.003 sec. Orbital periods : h from X-ray dips & eclipses and/or optical modulation > 15 well known bursting systems Low mass companions L x = erg/s  Neutron Stars in binary systems

March 11, 2003Lynn Cominsky - Cosmology A35030 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, 2003Lynn Cominsky - Cosmology A35031 X-ray Burst Sources  Burst spectra are thermal black-body Cominsky PhD 1981 L(t) = 4  R 2  T(t) 4 Radius Expansion Temperature 22

March 11, 2003Lynn Cominsky - Cosmology A35032 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

March 11, 2003Lynn Cominsky - Cosmology A35033 Soft Gamma Repeater Properties Superstrong magnetic dipole: B~ 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 = erg/s at peak of bursts  Young Neutron Stars near SNRs

March 11, 2003Lynn Cominsky - Cosmology A35034 SGR  Strong burst showing ~5 sec pulses  Change in 5 s spin rate leads to measure of magnetic field  Source is a magnetar!

March 11, 2003Lynn Cominsky - Cosmology A35035 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, 2003Lynn Cominsky - Cosmology A35036 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  = erg/s at peak of bursts  A cataclysmic event of unknown origin

March 11, 2003Lynn Cominsky - Cosmology A35037 The first Gamma-ray Burst  Discovered in 1967 while looking for nuclear test explosions - a 30+ year old mystery! Vela satellite

March 11, 2003Lynn Cominsky - Cosmology A35038 Compton Gamma Ray Observatory Eight instruments on corners of spacecraft NaI scintillators BATSE

March 11, 2003Lynn Cominsky - Cosmology A35039 CGRO/BATSE Gamma-ray Burst Sky  Once a day, somewhere in the Universe

March 11, 2003Lynn Cominsky - Cosmology A35040 The GRB Gallery When you’ve seen one gamma-ray burst, you’ve seen…. one gamma-ray burst!!

March 11, 2003Lynn Cominsky - Cosmology A35041 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

March 11, 2003Lynn Cominsky - Cosmology A35042 Breakthrough! In 1997, BeppoSAX detects X-rays from a GRB afterglow for the first time, 8 hours after burst

March 11, 2003Lynn Cominsky - Cosmology A35043 The View From Hubble/STIS 7 months later

March 11, 2003Lynn Cominsky - Cosmology A35044 On a clear night, you really can see forever! reached 9 th magnitude for a few moments! First optical GRB afterglow detected simultaneously

March 11, 2003Lynn Cominsky - Cosmology A35045 The Supernova Connection GRB 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, 2003Lynn Cominsky - Cosmology A35046 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

March 11, 2003Lynn Cominsky - Cosmology A35047 Iron lines in GRB  Chandra observations show link to hypernova model when hot iron-filled gas is detected from GRB Iron is a signature of a supernova, as it is made in the cores of stars, and released in supernova explosions

March 11, 2003Lynn Cominsky - Cosmology A35048 Catastrophic Mergers  Death spiral of 2 neutron stars or black holes

March 11, 2003Lynn Cominsky - Cosmology A35049 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, 2003Lynn Cominsky - Cosmology A35050 Gamma-ray Bursts  Either way you look at it – hypernova or merger model  GRBs signal the birth of a black hole!

March 11, 2003Lynn Cominsky - Cosmology A35051 Gamma-ray Bursts  Or maybe the death of life on Earth? No, gamma- ray bursts did not kill the dinosaurs!

March 11, 2003Lynn Cominsky - Cosmology A35052 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 GLAST balloon test

March 11, 2003Lynn Cominsky - Cosmology A35053 HETE-2  Launched on 10/9/2000  Operational and finding about 2 bursts per month

March 11, 2003Lynn Cominsky - Cosmology A35054 Swift Mission  Burst Alert Telescope (BAT)  Ultraviolet/Optical Telescope (UVOT)  X-ray Telescope (XRT) To be launched in 2003

March 11, 2003Lynn Cominsky - Cosmology A35055 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, 2003Lynn Cominsky - Cosmology A35056 Gamma-ray Large Area Space Telescope  GLAST Burst Monitor (GBM)  Large Area Telescope (LAT)

March 11, 2003Lynn Cominsky - Cosmology A35057 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, 2003Lynn Cominsky - Cosmology A35058 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, 2003Lynn Cominsky - Cosmology A35059 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 gamma- ray burst  This is similar to the way that the Interplanetary Network (IPN) really works  See

March 11, 2003Lynn Cominsky - Cosmology A35060 Web Resources :  GLAST E/PO web site  Swift E/PO web site  Imagine the Universe!  Science at NASA’s Marshall Space Flight Center  Supernova Cosmology Project  Ned Wright’s ABCs of Distance

March 11, 2003Lynn Cominsky - Cosmology A35061 Web Resources  Robert Duncan’s magnetar page  Chandra observatory  Jochen Greiner’s Gamma-ray bursts and SGR Summaries  HETE-2 mission  Compton Gamma Ray Observatory