Session A1: Plenary Session I

The Fermi Gamma-ray Space Telescope: The First Eight Months

The \textit{Fermi }Gamma-ray Space Telescope was launched by NASA on June 11, 2008. The Large Area Telescope (LAT) instrument measures cosmic gamma-ray radiation in the energy range 20 MeV to $>$300 GeV, with supporting measurements by the Gamma-ray Burst Monitor (GBM) for gamma-ray bursts from 8 keV to 30 MeV. The LAT, with a large improvement in sensitivity, large field-of-view, and much finer angular resolution compared to previous high-energy telescopes, observes 20{\%} of the sky at any instant and covers the entire sky every 3 hours\textit{. Fermi} is providing an important window on a wide variety of high-energy phenomena, including pulsars, black holes and active galactic nuclei; gamma-ray bursts; the origin of cosmic rays and supernova remnants; and searches for hypothetical new phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang.~ This talk will describe results obtained during the first eight months of the first year sky-survey phase of the \textit{Fermi }mission.   

What have we learned using the CEBAF microscope to study hadronic matter?

High-energy electrons are a remarkably clean probe of hadronic matter, essentially providing a microscope for examining atomic nuclei and the strong nuclear force. For more than a decade, the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab) has been a leading facility for such investigations, resulting in a number of surprising discoveries and a substantive refinement of our understanding of the nucleon, its underlying quark structure, and the dynamics of the strong interaction. The insights gained from research at JLab cover a broad range of length scales, monitored by the 4-momentum transfer Q$^{2}$, in elastic, inelastic, and deeply inelastic scattering regimes. One notable discovery has been the unexpected Q$^{2}$ variation of the ratio of the proton elastic form-factors G$^{p}_{E}$ / G$^{p}_{M}$, which suggests an important contribution from quark orbital angular momentum to the spin of the nucleon. This finding is further supported by spin-dependent deep-inelastic measurements, which also appear to require significant contributions from quark orbital angular momentum. Another notable achievement is the unambiguous observation of proton-neutron correlations in nuclei, a clear signature of the short-range piece of the nucleon-nucleon potential. This fulfills a long-standing quest in electron scattering and provides crucial input to the description of cold, dense nuclear matter ranging from terrestrial nuclei to neutron stars. Investigations at JLab have also benefitted from unconventional techniques, such as the use of parity-violation to access weak neutral current interactions as a probe of nuclear matter. This approach, which was employed in a sensitive search for contributions of virtual strange quarks to the nucleon charge and magnetic distributions, also yields significant new constraints on physics beyond the Standard Model.   

Merging Black Holes

The final merger of two black holes is expected to be the strongest gravitational wave source for ground-based interferometers such as LIGO, VIRGO, and GEO600, as well as the space-based LISA. Observing these sources with gravitational wave detectors requires that we know the radiation waveforms they emit. And, when the black holes merge in the presence of gas and magnetic fields, various types of electromagnetic signals may also be produced. Since these mergers take place in regions of extreme gravity, we need to solve Einstein's equations of general relativity on a computer. For more than 30 years, scientists have tried to compute black hole mergers 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. Within the past few years, however, this situation has changed dramatically, with a series of remarkable breakthroughs. This talk will focus on new simulations that are revealing the dynamics and waveforms of binary black hole mergers, and their applications in gravitational wave detection, testing general relativity, and astrophysics.