KICP Seminars & Colloquia, Fall 2012

Seminar schedule for Fall 2012
October 3, 2012
Astronomy Colloquium
David Charbonneau
Harvard University
How to Find the Nearest Habitable Exoplanet   [Abstract]
October 5, 2012
Friday noon seminar
Pasquale Blasi
INAF/Arcetri Astrophysical Observatory
Acceleration of Galactic Cosmic Rays   [Abstract]
October 10, 2012
Wednesday colloquium
Rafael F Lang
Purdue University
The Search for Dark Matter with XENON   [Abstract]
October 12, 2012
Friday noon seminar
A. Emir Gumrukcuoglu
Kavli IPMU, University of Tokyo
Fate of cosmological solutions in massive gravity   [Abstract]
October 17, 2012
Wednesday colloquium
Cheng Chin
The University of Chicago
From cosmology to cold atoms: observation of Sakharov acoustic oscillations in quenched atomic superfluids   [Abstract]
October 19, 2012
Friday noon seminar
Alex Geringer-Sameth
Brown University
Results of dark matter searches in dwarf galaxies with Fermi   [Abstract]
October 22, 2012
Open Group seminar
Tobias Baldauf
University of Zurich, Institute for Theoretical Physics
Halo Clustering beyond the Local Bias Model   [Abstract]
October 24, 2012
Wednesday colloquium
Juan I. Collar
University of Chicago
Direct Detection of WIMP dark matter: the nitty-gritty   [Abstract]
October 26, 2012
Friday noon seminar
Vera Gluscevic
California Institute of Technology
CMB as a Probe of New Physics: The Story of Cosmic Birefringence   [Abstract]
October 31, 2012
Astronomy Colloquium
Mansi Kasliwal
Carnegie Institution for Science
Bridging the Gap: Transients in the Local Universe   [Abstract]
November 2, 2012
Friday noon seminar
Caroline N Clark
Imperial College London
SPIDER, CMB Polarization And Modeling Polarized Microwave Foreground Emission   [Abstract]
November 7, 2012
Wednesday colloquium
Amol Upadhye
Argonne National Laboratory
Modified gravity from the micron to the megaparsec   [Abstract]
November 9, 2012
Friday noon seminar
Andrew Wetzel
Yale University
Galaxy evolution in groups and clusters in a hierarchical Universe   [Abstract]
November 14, 2012
Astronomy Colloquium
Drake Deming
University of Maryland at College Park
Infrared Spectroscopy of Extrasolar Planetary Atmospheres   [Abstract]
November 16, 2012
Friday noon seminar
Tim R Linden
UC - Santa Cruz
Understanding High Energy Gamma-Ray Emission from the Galactic Center   [Abstract]
November 28, 2012
Astronomy Colloquium
Guangtun Ben Zhu
John Hopkins University
Probing Gas Halos of Galaxies with SDSS   [Abstract]
November 30, 2012
Friday noon seminar
Daniel Grin
Institute for Advanced Study
New light on cosmic initial conditions and dark matter   [Abstract]
December 3, 2012
Astronomy Special Seminar
Steve Federman
Molecular Data for Interstellar Studies: CO, CH, and C2   [Abstract]
December 4, 2012
Astronomy Special Seminar
Steve Federman
Probing Stellar Nucleosynthesis through Interstellar Isotope Ratios   [Abstract]
December 4, 2012
Special seminar
Alex Drlica-Wagner
Stanford
Searches for Galactic Dark Matter with the Fermi-LAT: Current Status and Future Outlook   [Abstract]
December 5, 2012
Astronomy Colloquium
Rob Simcoe
Heavy-Element Enrichment in the Early Universe Observed with FIRE   [Abstract]
December 7, 2012
Friday noon seminar
Simeon Bird
Institute for Advanced Study, Princeton
Neutral Hydrogen Absorption on a Moving Mesh   [Abstract]
December 20, 2012
Open Group seminar
Riccardo DeSalvo
KAGRA, ICRR, University of Tokyo
Potentials for Astronomical Observations   [Abstract]
 
WEDNESDAY COLLOQUIA

  • October 10, 2012 | 3:30 PM | BSLC 001
    The Search for Dark Matter with XENON
    Rafael F Lang, Purdue University

    We know that most of the matter in the Universe is Dark Matter, but we don't know what Dark Matter is made of. Current and upcoming detectors have the sensitivity to detect or exclude Weakly Interacting Massive Particles (WIMPs) as candidates for Dark Matter. In this talk, I will review the basics of the direct search for WIMPs and give a quick overview of the current status of the field. The XENON100 experiment in particular is a leading experiment in this search and will be presented in some detail, together with recent results from a search in 225 live days of data. An outlook on where we are headed in the next few years will be given.
  • October 17, 2012 | 3:30 PM | BSLC 001
    From cosmology to cold atoms: observation of Sakharov acoustic oscillations in quenched atomic superfluids
    Cheng Chin, The University of Chicago

    Sakharov oscillation, conventionally discussed in the context of early universe evolution and the anisotropy of cosmic microwave background radiation, is the manifestation of interfering acoustic waves generated in an ideal fluid. We report a laboratory observation of Sakharov oscillations in a quenched atomic superfluid. We quench the interactions between atoms and monitor the subsequent density fluctuations at different time and length scales. Sakharov oscillations are identified as the multi-peak structure in the density power spectrum, resembling that of the cosmic microwave background radiation. From the oscillations, we determine the sonic horizon, providing new perspectives to extend quantum simulation to other intriguing cosmological and gravitational phenomena
  • October 24, 2012 | 3:30 PM | BSLC 001
    Direct Detection of WIMP dark matter: the nitty-gritty
    Juan I. Collar, University of Chicago

    I'll present an update on the status of dark matter direct detection experiments, with particular emphasis on details that the non-experimentalist may ignore, or the experimentalist may hide. I will also focus on local activities in this area (COUPP, CoGeNT, DAMIC, and dedicated calibration experiments for a number of target materials).
  • November 7, 2012 | 3:30 PM | BSLC 001
    Modified gravity from the micron to the megaparsec
    Amol Upadhye, Argonne National Laboratory

    The observed cosmic acceleration hints at a low-energy modification to General Relativity which could give rise to fifth forces and new particles. After describing f(R), chameleon, and symmetron models, I will discuss constraints on the resulting fifth forces from laboratory torsion pendulum experiments, the stability of stars, and the dynamics of large-scale cosmic structure. In particular, laboratory experiments are on the verge of testing interesting classes of chameleon and symmetron fifth forces. I will also show how new particles predicted by these models, which might be produced through photon interactions in stars or the laboratory, can be used to constrain modifications to gravity.

 
FRIDAY NOON SEMINARS

  • October 5, 2012 | 12:00 PM | LASR Conference Room
    Acceleration of Galactic Cosmic Rays
    Pasquale Blasi, INAF/Arcetri Astrophysical Observatory

    I will discuss the crucial role played by two phenomena that have recently been investigated in the context of cosmic ray (CR) acceleration in Galactic sources (but not only): 1) plasma instabilities induced by the streaming of accelerated particles ahead of a shock front; 2) presence of neutral atoms in the acceleration region. Both effects play a crucial role in non-linear theories of CR acceleration at shock fronts. The former is especially crucial for creating the level of magnetic turbulence required to explain both high maximum energies and the observed X-ray rims in supernova remnants. The presence of neutrals has been shown to lead to several diagnostics of the acceleration process, such as the anomalous broadening of Balmer lines from supernova shocks. Moreover, given the collisionless nature of supernova shocks (and of most astrophysical shocks) neutrals behave very differently from ions and can be shown to lead to steeper spectra of accelerated particles, as a consequence of the shock modification due to the coupling of neutrals to ions through charge exchange reactions and ionization. I will discuss these topics in direct connection with the problem of the origin of Galactic cosmic rays.
  • October 12, 2012 | 12:00 PM | LASR Conference Room
    Fate of cosmological solutions in massive gravity
    A. Emir Gumrukcuoglu, Kavli IPMU, University of Tokyo

    Massive gravity has self-accelerating solutions, which may account for the present day acceleration without the need for a bare cosmological constant. Generically, the value of the graviton mass is of the order of Hubble rate today. But are these solutions stable?
    The construction of a finite-range gravity theory has been one of the major challenges in classical field theory for the last 70 years. Recently, de Rham, Gabadadze and Tolley constructed a nonlinear theory of massive gravity, which successfully removes the unwanted extra degree that contaminated earlier constructions. The theory allows for homogeneous and isotropic solutions with self acceleration, providing an alternative to dark energy. However, the perturbation analysis shows that at linear level, these solutions contain only 2 propagating degrees of freedom, as opposed to 5 expected from a massive spin-2 particle. I will show that at nonlinear order, the additional 3 degrees acquire non-vanishing kinetic terms. For one of these degrees, the sign of the kinetic term is always negative, leading to a ghost instability in the homogeneous and isotropic background. I will conclude by presenting a new anisotropic solution which looks isotropic at the background level. For this solution, the nonlinear ghost which appears in the purely isotropic solution may be evaded.
  • October 19, 2012 | 12:00 PM | LASR Conference Room
    Results of dark matter searches in dwarf galaxies with Fermi
    Alex Geringer-Sameth, Brown University

    Image credit: NASA/DOE/Fermi-LAT Collaboration/Koushiappas and Geringer-Sameth/Brown University
    I will present new results from a search for both continuum and line emission from dark matter annihilation in Milky Way dwarfs. These results are based on the joint analysis of dwarf galaxy data from the Fermi Gamma-ray Space Telescope using a statistically optimal weighting of individual photons including both spatial and spectral information. This new technique, applied to the indirect dark matter search, is strong enough to probe generic WIMP candidates that reproduce the relic abundance. I will discuss the details of the framework and how it may be applied to other situations, including making predictions for future experiments.
  • October 26, 2012 | 12:00 PM | LASR Conference Room
    CMB as a Probe of New Physics: The Story of Cosmic Birefringence
    Vera Gluscevic, California Institute of Technology

    Cosmological birefringence is a postulated rotation of the linear polarization of photons that arises due to a Chern-Simons coupling of a new scalar field to electromagnetism. In particular, it appears as a generic feature of simple quintessence models for Dark Energy, and therefore, should it be detected, could provide insight into the microphysics of cosmic acceleration. Prior work has sought this rotation, assuming the rotation angle to be uniform across the sky, by looking for the parity-violating TB and EB correlations in the CMB temperature/polarization. However, if the scalar field that gives rise to cosmological birefringence has spatial fluctuations, then the rotation angle may vary across the sky. In this talk, I will present the results of the first CMB-based search for direction-dependent cosmological birefringence, using WMAP-7 data, and report the first constraint on the rotation-angle power spectrum for multipoles up to the resolution of the instrument. I will discuss the implications for a specific (scale-invariant) model for rotation, and show forecasts for Planck and future experiments. I will then briefly comment on other parity-violating physical models, such as chiral gravity, and show how they can be distinguished from birefringent rotation. I will conclude by demonstrating how the same analysis can be used to probe inhomogeneous cosmic reionization, and discuss current constraints on a simple reionization model whose parameters can be figures of merit for future experiments.
  • November 2, 2012 | 12:00 PM | LASR Conference Room
    SPIDER, CMB Polarization And Modeling Polarized Microwave Foreground Emission
    Caroline N Clark, Imperial College London

    I will give a brief update on the SPIDER experiment, a suborbital polarimeter aimed at detecting B-mode polarization of the CMB. Given that foregrounds are expected to dominate the potential B-mode signal over all targeted observing frequencies, I will move on to present templates of the dominant Galactic foreground emissions, synchrotron and thermal dust. I will describe the inputs to this model, which includes a 3D description of the Galactic magnetic field on large and small scales as well as the dust and cosmic ray density distributions and details of alignment mechanisms. These templates may prove useful for testing foreground contamination levels in patches targeted by experiments and component separation methods and in constraining parameters in Galactic magnetic field models. I will confront the model with some available data, namely the WMAP MCMC templates of foreground emission, as an indication of the reliability of the model.
  • November 9, 2012 | 12:00 PM | LASR Conference Room
    Galaxy evolution in groups and clusters in a hierarchical Universe
    Andrew Wetzel, Yale University

    Satellite galaxies in groups and clusters play a critical role in the picture of galaxy evolution. As many as a third of all galaxies are satellites, and satellite star formation quenching is the dominant process in building the red-sequence population at low mass. I will present an observational and theoretical investigation into the evolution of star formation in satellite galaxies, using the Sloan Digital Sky Survey to examine satellites across a wide range of host halo masses, from massive clusters to the lowest mass dwarf galaxy groups in the local Universe. I will place these results in a fully cosmological context using a high-resolution simulation to track satellite orbits and infall times, showing that satellite star formation histories follow a delayed-then-rapid quenching scenario. I also will examine the curious evolution of satellites that orbit beyond their host halo's virial radius.
  • November 16, 2012 | 12:00 PM | LASR Conference Room
    Understanding High Energy Gamma-Ray Emission from the Galactic Center
    Tim R Linden, UC - Santa Cruz

    Recent data taken at TeV energies (by Atmospheric Cherenkov Telescopes) and at GeV energies (by the Fermi-LAT) have opened a new window into studies of the Galactic center. The high angular resolution of these observations make them especially well-suited to understanding the many energetic processes occurring in this dense region. Interestingly, Fermi-LAT observations have uncovered an apparent excess of ~1 GeV photons peaked around the galactic center compared to the smooth power-law observed by TeV telescopes. In this talk, I will discuss several convincing models for the peculiar emission spectrum and morphology in this region, including the annihilation of particle dark matter, a yet-undiscovered population of millisecond pulsars, and hadronic emission processes from the central black hole. Additionally I will consider the extremely interesting observation by Weniger (2012) indicating the observation of a gamma-ray line by the Fermi-LAT with an energy of 130 GeV, and will briefly discuss the instrumental, dark matter, and astrophysical phenomena which may be responsible for this observation.
  • November 30, 2012 | 12:00 PM | LASR Conference Room
    New light on cosmic initial conditions and dark matter
    Daniel Grin, Institute for Advanced Study

    Deviations from adiabaticity and Gaussianity in the early universe may shed light on the physics seeding primordial fluctuations. I will discuss statistical techniques to extract local-type non-Gaussianity in the presence of the full CMB transfer function. I will discuss CMB methods to probe isocurvature fluctuations between baryons and dark matter (undetectable in linear theory), as well as a new limit to this mode. Extremely light axionic dark matter (m < 10^{-18}) is in theoretical vogue, and I will discuss ongoing work to search for such axions using large scale structure and the CMB. I will close with the results of a new telescope search for decaying relic axions.
  • December 7, 2012 | 12:00 PM | LASR Conference Room
    Neutral Hydrogen Absorption on a Moving Mesh
    Simeon Bird, Institute for Advanced Study, Princeton

    I will present recent work performing cosmological simulations using the new moving mesh technique implemented in Arepo. Specifically, I have looked at the distribution of damped Lyman-alpha absorbers in Arepo, as compared to the SPH code Gadget. I have also compared the Lyman-alpha forest region between the two codes. Since both Arepo and Gadget use identical gravity solvers, but different methods for solving the Euler equations, we can use this comparison to assess how numerical effects associated with the hydro-solver impact observable results.

 
SPECIAL SEMINARS

  • December 4, 2012 | 1:00 PM | LASR Conference Room
    Searches for Galactic Dark Matter with the Fermi-LAT: Current Status and Future Outlook
    Alex Drlica-Wagner, Stanford

    During the past four years the Fermi Large Area Telescope (LAT) has given us an unprecedented view of the universe at GeV energies. New astrophysical source classes abound, creating a picture of the gamma-ray sky that is far more interesting and complicated than previously envisioned. Hidden among astrophysical gamma-ray emission is the potential for an additional gamma-ray component arising from the annihilation (or decay) of particle dark matter. Here, I will give an overview of current LAT searches for dark matter annihilation in the local Galactic environment. I will focus specifically on searches for dwarf spheroidal satellite galaxies, unassociated dark matter substructures, and the smooth Galactic dark matter halo. I will also briefly touch on recent observations of a high-energy spectral feature coincident with the Galactic center. I will finish by discussing how future searches for Galactic dark matter will benefit from a better understanding of the LAT instrument and from a more complete census of the local dark matter distribution as determined by optical surveys.

 
OPEN GROUP SEMINARS

  • October 22, 2012 | 10:30 AM | LASR Conference Room
    Halo Clustering beyond the Local Bias Model
    Tobias Baldauf, University of Zurich, Institute for Theoretical Physics

    The clustering of galaxies in ongoing and upcoming galaxy surveys contains a wealth of cosmological information. Extracting this information is a non-trivial task since galaxies and their host haloes are stochastic tracers of the non-linear matter density field. The relation between matter and halo distribution is commonly expressed in terms of a local bias model. Recent studies have revealed inconsistencies between the simple local Eulerian bias model and simulations. I will explain two effects that can explain and partially cure these inconsistencies. Firstly, non-local bias terms proportional to the tidal tensor are generated by gravitational evolution and their presence can be detected in the halo bispectrum. Secondly, I will explain how discreteness of haloes and their small scale exclusion alters the large scale halo power spectrum.
  • December 20, 2012 | 11:00 AM | LASR Conference Room
    Potentials for Astronomical Observations
    Riccardo DeSalvo, KAGRA, ICRR, University of Tokyo

    This seminar is divided into two parts. The first part is intended for the general physics and astrophysics public. I will present a survey of some of the potentialities of Gravitational Wave Astronomy, which just started, briefly introduce how we detect gravitational waves, and what it takes to turn detection into astronomical observations. I will make the point of where we stand, what was achieved with the first generation of detectors, outline how far we can get with the second generation being commissioned, and illustrate some aims of the third generation, presently being considered. I will make examples of what we started learning of astrophysics with the present observations, illustrate what can and should be done to get to true gravitational wave astronomy, make some example of challenges and problems that we had to solve, and some that still need to be tackled to get there. The emphasis will always be on ground based detection. Space base observatories will just be mentioned, because of limitations of time, and lack of my experience. The second part of the seminar will be more technical, intended for people interested in solid state physics and metallurgy. I will focus on seismic attenuation, one of the challenges that may appear of having been solved. I will speak on how the engineering problems have been very successfully solved for the first and second generation of Gravitational wave detectors. I will show how a fundamental material problem emerged and how we discovered a completely new regime of dissipation and deviation from the laws of elasticity. Starting from the Granato Lueck theory of elasticity and dislocations, we got to entanglement of dislocation leading to Self Organized Criticality behavior, non-causal response and mechanical noise. The new discovery, forced by the tight requirements of gravitational wave detectors, not only allows the choice of better materials for the seismic attenuation for the third generation observatories, but also for metrology instruments, and many other vibration sensitive apparata. It also explains the source of mechanical noise in seismometers and other inertial sensors and will lead (it already has), to the design of better instruments for geophysics and diagnostics.

 
ASTRONOMY COLLOQUIA

  • October 3, 2012 | 3:30 PM | KPTC 206
    How to Find the Nearest Habitable Exoplanet
    David Charbonneau, Harvard University

    The Giant Magellan Telescope and the James Webb Space Telescope may grant us the opportunity to study the atmospheres of potentially habitable worlds orbiting nearby stars. There is only one problem: We don't yet know at which stars we should point these observatories. Using data from the NASA Kepler Mission, we can deduce the distance within which we can expect a few such worlds, and hence the observational effort that will be required to characterize them. It appears extremely likely that the nearest systems will orbit low-mass M-dwarf stars, which is fortunate as the small physical sizes and low-luminosities of the stars permit novel ground-based detection schemes that are not feasible for Sun-like stars. The MEarth Project is an array of automated telescopes that survey several thousand of the closest and least massive stars to search for transiting planets. In pursuit of this quest, MEarth has informed our understanding of the physics governing the structure, evolution, and rotation of the most common stars in the galaxy.
  • October 31, 2012 | 3:30 PM | BSLC 001
    Bridging the Gap: Transients in the Local Universe
    Mansi Kasliwal, Carnegie Institution for Science

    With the advent of advanced gravitational wave interferometers and high energy neutrino facilities within this decade, the prospect of searching for their electromagnetic counterparts is promising. I discuss the challenge of poor sky localization, and present a simple solution that leverages the sensitivity limit to the local universe. Next, I discuss the rapidly growing inventory of transients in the local universe. Until recently, the framework of cosmic explosions was plagued with a glaring six-magnitude luminosity "gap" between the brightest novae and faintest supernovae. Systematic synoptic surveys, serendipitous discoveries and archival searches have started uncovering transients fainter, faster and rarer than supernovae only in the past few years. There is now evidence of multiple, distinct populations of rare transients in this gap. Each new class can illuminate a missing piece in our understanding of stellar evolution. Here I present discoveries and unique physics of transients that bridge this gap between novae and supernovae.
  • November 14, 2012 | 3:30 PM | BSLC 001
    Infrared Spectroscopy of Extrasolar Planetary Atmospheres
    Drake Deming, University of Maryland at College Park

    The geometry of transiting extrasolar planets provides rich scientific opportunities to probe their atmospheres using photometric and spectroscopic techniques. These techniques include detection of thermal emission at secondary eclipse using Spitzer and ground-based infrared detectors, as well as transmission spectroscopy using both the NICMOS and WFC3 instruments on Hubble, and ground-based telescopes as well. I will give my version of the current "scorecard" for exoplanetary spectroscopy, describing those results that I believe to be robust, versus those that are questionable, and I will show new results from Hubble WFC3 that promise to resolve some outstanding issues. In the future, we look forward to exoplanetary spectroscopy using JWST, and to a major role for the new generation of extremely large ground-based telescopes.
  • November 28, 2012 | 3:30 PM | BSLC 001
    Probing Gas Halos of Galaxies with SDSS
    Guangtun Ben Zhu, John Hopkins University

    The distribution of gas around galaxies - the circumgalactic and intergalactic media - contains signatures of key processes of galaxy formation such as outflows and accretion, and may account for the majority of baryons in the Universe. Absorption-line spectroscopy is a powerful tool to probe gas properties. SDSS has obtained spectroscopy for ~200,000 quasars, providing a perfect dataset for statistical analyses of absorption lines. I will introduce the new techniques we have developed to model quasar spectra and detect absorption lines. With these new tools, we have compiled a metal absorber catalog of ~50,000 systems. I will present a statistical analysis of these absorber systems and discuss implications for gas flow processes. In addition, our results allow us to measure the Galaxy-Gas correlation out to Mpc scales, linking the gas properties of individual galaxies to their large-scale environment.
  • December 5, 2012 | 3:30 PM | BSLC 001
    Heavy-Element Enrichment in the Early Universe Observed with FIRE
    Rob Simcoe,

    Many Chicago astronomers have used the FIRE spectrometer, an infrared echelle instrument on the Magellan/Baade telescope which has now been in operation for 2.5 years. One of my group's main scientific motivations for building FIRE was to observe heavy elements in quasar absorption spectra at the highest possible redshifts. In this colloquium I will report on new science and discoveries about the z ~ 6 universe that have resulted from FIRE's early operations. These include a new survey of circum-galactic metal pollution seen in MgII - previously only characterized at z < 2 - out to z=5.5. Also, we have substantially improved constraints on the CIV mass density and intergalactic carbon enrichment at z = 5.0-6.5. Finally, I will describe our first measurements of chemical abundances in the z > 7 universe, and discuss their significance for reionization and the formation of the first stars.

 
ASTRONOMY SPECIAL SEMINARS

  • December 3, 2012 | 3:00 PM | TAAC 67
    Molecular Data for Interstellar Studies: CO, CH, and C2
    Steve Federman,

    Ultraviolet data acquired with the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer have wide spectral bandpasses and high signal-to-noise ratios, thereby providing the means to detect relatively weak features from atoms and molecules. Here I focus on our analyses of transitions in CO, CH, and C2 associated with diffuse molecular clouds. The comparisons with well-characterized absorption bands allows us to derive oscillator strengths (or equivalently absorption cross sections), which have led to an improved understanding of the molecule's structure. The high-quality astronomical spectra also yield predissociation rates that provide further insight into the structure. Where possible, comparison with experimental and theoretical results will be highlighted.
  • December 4, 2012 | 12:00 PM | TAAC 41
    Probing Stellar Nucleosynthesis through Interstellar Isotope Ratios
    Steve Federman,

    High-resolution spectra of diffuse molecular clouds allow us to study isotope ratios for lithium and rubidium. These ratios provide information on the contributions from massive stars to Li and Rb production in the current epoch, which will be the focus of my talk. Cosmic-ray spallation, where relativistic protons break apart interstellar CNO nuclei, is a key process for the synthesis of light elements, including Li. For neutron-capture elements such as Rb, the weak s-process, where neutron capture is slower than beta decay, and the r-process are important. The weak s-process occurs in the He- and C-burning shells of the stars, while the r-process is thought to arise during the core-collapse supernova at the end of the star's life. Cosmic rays are accelerated to relativistic energy in the supernova event.