Astrophysics Science Division Colloquium Series
Schedule: January - March 2007

Astrophysics Science Division Colloquium Series
Schedule: January - March 2007

Through the courtesy of the speakers since 2004, most presentations are available on line.

Future schedules:

  • 2007, Second Quarter
  • Past schedules:

  • 2006, Fourth Quarter
  • 2006, Third Quarter
  • 2006, Second Quarter
  • 2006, First Quarter
  • 2005, Fourth Quarter
  • 2005, Third Quarter
  • 2005, Second Quarter
  • 2005, First Quarter
  • 2004, Fourth Quarter
  • 2004, Third Quarter
  • 2004, Second Quarter
  • 2004, First Quarter
  • 2003, Fourth Quarter

  • Time: 3:45 pm (Meet the Speaker at 3:30 pm) - Location: Bldg 21, Room 183 - unless otherwise noted.
    To view the abstract of a seminar, click on the title.


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
    1 2 3 4 5 6
    7 8 9 10 11 12 13
    14 15 16: Ioannis Contopoulos (Academy of Athens) - The Role of Reconnection in the Pulsar Magnetosphere" 17 18 19 20
    21 22 23: Joan Centrella (NASA/GSFC) - Postponed to Feb. 6 24 25 26 27
    28 29 30: Suzanne Staggs (Princeton) - Cosmology and the Atacama Cosmology Telescope 31


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
    1 2 3
    4 5 6: Joan Centrella (NASA/GSFC) - (Postponed to Mar 27) 7 8 9 10
    11 12 13 14 15 16: Matthias Beilicke (Univ. Hamburg) - The unidentified, extended TeV gamma-ray source HESS J1303-631 and fast variability of radio galaxy M87 observed with H.E.S.S. 17
    18 19 20 Cara Rakowski (NRC, NRL) - The Partitioning of Energy among Electrons, Ions, and Cosmic Rays at Collisionless Shocks in SNRs. 21 22 23 24
    25 26 27 28


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
    1 2 3
    4 5 6 7 8 9 10
    11 12 13 Charles Keeton (Rutgers) - Testing Theories of Gravity with Black Hole Lensing 14 15 16 17
    18 19 20 Lance Miller (Oxford Univ.) - Supermassive black holes: their growth and the link to galaxy formation 21 22 23 24
    25 26 27: Joan Centrella (NASA/GSFC) - Binary Black Holes, Gravitational Waves, and Numerical Relativity 28 29 30 31

    The Role of Reconnection in the Pulsar Magnetosphere

    Ioannis Contopoulos

    Academy of Athens

    Tuesday, January 16, 2007


    We will present an overview of our current understanding of the structure of the pulsar magnetosphere. We will show that ideal MHD is a valid description of the largest part of the magnetosphere except for a thin equatorial region where the main magnetospheric electric current flows. We will show that equatorial reconnection is related to the global magnetic field topology, and therefore it cannot be studied independently. We will argue that reconnection efficiency may be measurable through the pulsar braking index. Finally, we will argue that equatorial reconnection is able to accelerate particles that reach the pulsar wind termination shock with energies of the order of 10^16 eV.

    Cosmology and the Atacama Cosmology Telescope (ACT)

    Suzanne Staggs


    Tuesday, January 30, 2007


    The Atacama Cosmology Telescope (ACT) is a new 6m millimeter-wave telescope in the high dry desert of Chile. The ACT team is outfitting the telescope with three kilopixel arrays of TES bolometer detectors made at NASA/GSFC. The ACT cameras will image the sky at three different frequencies with arcminute resolution and microKelvin sensitivity. These maps will allow characterization of the cosmic microwave background (CMB) angular power spectrum out to very small angular scales (never before measured). Since the WMAP data constrain most of the other relevant cosmological parameters with their measurements of the larger-angular-scale part of the spectrum, these new ACT measurements can reveal something about the initial conditions of the primordial power spectrum of density fluctuations. The ACT maps will also encode information about the intervening universe between the primordial plasma at redshift 1000 and the present epoch, in the form of spatial correlations imparted to the microwave fluctuations by gravitational lensing of the matter in the lines of sight. Finally, the three frequencies of the ACT detector arrays have been chosen for ready identification of the spectral distortions the CMB spectrum develops upon scattering from the hot electrons in clusters of galaxies. Thus, ACT will catalog (nearly) all the clusters in the fields it observes. The ACT project includes follow-up to determine cluster redshifts. We will elaborate on these science goals, and also describe the experiment in some detail.

    Binary Black Holes, Gravitational Waves, and Numerical Relativity

    Joan Centrella

    NASA/Goddard Space Flight Center

    Tuesday, March 27, 2007


    The final merger of two black holes releases a tremendous amount of energy and is one of the brightest sources in the gravitational wave sky. Observing these sources with gravitational wave detectors requires that we know the radiation waveforms they emit. Since these mergers take place in regions of extreme gravity, we need to solve Einstein's equations of general relativity on a computer in order to calculate these waveforms.

    For more than 30 years, scientists have tried to compute these waveforms using the methods of numerical relativity. The resulting computer codes have been plagued by instabilities, causing them to crash well before the black holes in the binary could complete even a single orbit. REcently this situation has changed dramatically, with a series of amazing breakthroughs. This talk will take you on this quest for the holy grail of numerical relativity, showing how a spacetime is constructed on a computer to build a simulation laboratory for binary black hole mergers. We will focus on the recent advances that are revealing these waveforms, and the dramatic new potential for discoveries that arises when these sources will be observed by LISA and LIGO.

    The Unidentified, Extended TeV Gamma-ray Source HESS J1303-631 and Fast Variability of Radio Galaxy M87 Observed with H.E.S.S.

    Matthias Beilicke

    University Hamburg

    Friday, February 16, 2007

    Time: 11am / Location: Bldg 2, Rm 8


    The TeV gamma-ray source HESS J1303-631 was serendipitously discovered in the field of view of the binary system PSR B1259-63 by the H.E.S.S. Cherenkov telescopes in 2004. A counterpart at other wavelengths was not found so far, making HESS J1303-631 an unidentified TeV gamma-ray source. Results from the TeV gamma-ray observations and implications are presented. The giant radio galaxy M87 was observed by H.E.S.S. in 2003-2006. The observations confirm M87 as the first extragalactic TeV gamma-ray source not of the blazar type (first indications of a signal were reported by the HEGRA collaboration earlier). The TeV gamma-ray flux was found to be variable on time-scales of days which strongly constrains the size of the emission region. The results as well as theoretical interpretations will be presented.

    The Partitioning of Energy among Electrons, Ions, and Cosmic Rays at Collisionless Shocks in SNRs.

    Cara E. Rakowski

    NRC Fellow, Naval Research Lab

    Tuesday, February 20, 2007


    The outer blast-waves of supernova remnants (SNRs) are an example of ``collisionless shocks'', i.e. the width of the shock transition is tiny compared to the Coulomb mean-free-path. In these shocks the particle heating to postshock temperatures and acceleration to cosmic ray energies must be mediated by plasma waves arising from instabilities, and not just from random Coulomb collisions. The 1/1835 mass ratio of electrons to protons makes the heating and acceleration of electrons particularly difficult. In this talk I will explain the spectroscopic techniques for determining the proton, ion and electron temperatures at a variety of supernova remnant shocks, and present the latest data on the electron to proton temperature ratio from this survey. The observed inverse square dependence of the electron to proton temperature ratio with shock velocity can be explained by a physical model for the electron heating, whereby lower hybrid waves excited in the shock cosmic-ray precursor damp by accelerating electrons along the local magnetic field, echoing recent suggestions in the literature that the cosmic rays are an integral part of the collisionless shock structure.

    Testing Theories of Gravity with Black Hole Lensing

    Charles Keeton

    Dept. of Physics, Rutgers

    Tuesday, March 13, 2007


    The gravitational deflection of light provided one of the first observational confirmations of general relativity. Now I am considering how gravitational lensing can provide a stronger and more fundamental test of Einstein's theory, and of intriguing new alternatives. I will introduce a rigorous and comprehensive analytical framework for black hole lensing, and use it to make concrete predictions that are testable with current or near-future technology. Here are two examples: (1) In post-post-Newtonian theories of gravity, there are universal relations among lensing observables. Observed violations of these relations would falsify all PPN models in one fell swoop. (2) In braneworld gravity, there could be many primordial black holes (even in our Solar System) that may be detectable in "attolensing" of gamma ray bursts observed by GLAST.

    Supermassive Black Holes: Their Growth and the Link to Galaxy Formation

    Lance Miller

    Dept. of Physics, Oxford

    Tuesday, March 20, 2007


    We now recognise that every massive galaxy contains a supermassive black hole at its heart, and that the growth of those black holes is both observed in the luminous phases of active galactic nuclei (AGN) and quasars, and is likely responsible for the observed hard X-ray background. We still don't understand what the relationship is between black hole growth and galaxy growth, or why accretion onto black holes turned off as the universe evolved towards the present day. I will argue that in fact black hole growth, and hence AGN evolution, is intimately connected to galaxy growth, and that AGN cosmological evolution has a natural explanation within hierarchical galaxy formation.

    Jerry Bonnell
    NASA Logo, National Aeronautics and Space Administration