Quantum Geometry and Interferometry

Craig Hogan

Fermilab/U Chicago

Tuesday, Jan 15, 2013

Abstract

Experiments with quantum particles prove that the real world is nonlocal: nothing ever happens at a definite time or place. Theory suggests that gravity and space-time also emerge from a quantum system, but no quantum behavior of space-time itself has ever been measured experimentally. The talk will describe how the techniques of interferometry, created to study gravitational waves from motions in the distant universe, are being adapted to study the quantum properties of space and time on the smallest scales.

Particle acceleration in astrophysical collisionless shocks

Anatoly Spitkovsky

Princeton

Tuesday, Jan 29, 2013

Abstract

Nonthermal emission from many astrophysical sources, including relativistic jets and supernova remnants, is often attributed to collisionless shocks. These shocks are inferred to accelerate particles and in some cases strongly amplify magnetic fields. How this happens in detail remains to be clarified through both theory and observations. In this talk, I will present a summary of recent progress in numerical modeling of collisionless shocks using first-principles plasma simulations. I will discuss the internal structure of collisionless shocks, concentrating on the conditions necessary for particle acceleration. I will present simulations which show ab-initio Fermi acceleration of particles from the thermal pool to power-law distributions, which sets constraints on the shock acceleration efficiency and field geometry in astrophysical flows. Other results that will be discussed include the amplification of magnetic fields by accelerated particles through streaming instabilities, and the electron-ion temperature equilibration in shocks. I will conclude with the applications of shock simulations to the physics of gamma-ray bursts, pulsar wind nebulae, and supernova remnants, and the prospects for testing the physics of collisionless shocks in laboratory experiments.

Synchronous X-ray and Radio Mode Changing in Pulsar B0943+10: Evidence for a Rapid Global Transformation of the Magnetosphere

Joanna Rankin

U Vermont

Tuesday, Feb 5, 2013

Abstract

Pulsars are remarkable sources, capable of producing EM emission from low-frequency radio waves up to high-energy gamma-rays -- and from sites close to the neutron-star surface out to the edges of the magnetosphere. Some pulsars also exhibit several stable "modal" states with fascinating modulation properties and in some cases even different spindown torques. B0943+10 has two such radio modes, one with a carousel of bright accurately drifting subpulses and another with weak chaotic pulses. Correlated mode changes in the radiation at different wavelengths are then key to understanding the physical connections and mechanisms of the emission regions. Through simultaneous observations with the GMRT, LOFAR, and XMM-Newton observatories, we have detected synchronous switching in the radio and X-ray emission properties of B0943+10. When the pulsar is in its radio "bright" mode, the X-rays are unpulsed and have a non-thermal spectrum. Conversely, when the pulsar is in a radio "quiet" mode, the X-ray luminosity more than doubles and a 100%-pulsed thermal component is observed along with the non-thermal radiation. This indicates rapid, global changes in magnetospheric conditions, which challenge all proposed pulsar emission theories.

The Highest Energy Cosmic Particles

Angela Olinto

U Chicago

Tuesday, Feb 12, 2013

Abstract

The origin of cosmic rays is a century old mystery. Observed over 12 orders of magnitudes in energy, these particles can reach macroscopic energies of 10²⁰ eV (or 16 Joules). At the highest energies, sources should be among the most powerful extragalactic accelerators. Possible explanations have narrowed down with the observation of a "GZK-like" spectral feature and hints of anisotropies in the distribution of arrival directions. These hints raise hopes for cosmic ray astronomy, however, composition indicators point to a different interpretation. Are hadronic interactions changing at the highest energies or are primaries heavy at the highest energies? A clear resolution of this mystery calls for much larger statistics than the reach of current observatories.

X-rays Surveys: Past, Present and Future

Steve Murray

JHU

Tuesday, Feb 26, 2013

Abstract

The X-ray sky is filled with a variety of sources ranging from nearby common stars to exotic super-massive black holes at the centers of distant galaxies. The story of how we have come to know of these objects spans about 50 years of X-ray observations. Key to the discovery of the complex and beautiful X-ray universe are the various large surveys that have been carried out with ever increasing sensitivity and precision. I will review several of these missions, highlighting some of their major discoveries, and then summarize the more recent survey work being done with currently operating facilities. Finally, I will discuss plans for the future, in particular new missions to carry out sensitive all-sky or large area surveys surpassing by orders of magnitude those last done in the 1990's.

X-ray imaging with high angular resolution: resolving the structure of the hot gas near the cluster virial radius with Chandra and prospects for a major Chandra successor

Alexey Vikhlinin

CfA

Tuesday, Mar 5, 2013

Abstract

Ability to image the X-ray sky with sub-arcsec angular resolution is the primary reason for success of the Chandra X-ray Observatory and this mission's amazing scientific versatility. Chandra imaging capabilities often become a deciding factor even in non-obvious application. As an example, I will discuss the results from a recent 2 Ms Chandra observation of Abell 133, where we were able to isolate multiply infalling substructures, trace the smoothly distributed intracluster gas to the virial radius, and possibly observe the emergence of the cosmic web filaments beyond this radius.

Looking into the future, a major successor for Chandra will need to maintain at least the same level of the angular resolution. I will discuss a concept and enabling technologies for such a mission, SMART-X. It is a concept for a next-generation X-ray observatory with large-area, 0.5" resolution grazing incidence adjustable X-ray mirrors; high-throughput critical transmission gratings, and X-ray micro calorimeter and CMOS-based imager in the focal plane. High angular resolution is enabled by new technology based on controlling the shape of mirror segments using thin film piezo actuators deposited on the back surface. Science application include observations of growth of supermassive black holes since redshifts of ~10, ultra-deep surveys overs 10's of square degrees, galaxy assembly at z=2-3, as well as new opportunities in the high-resolution X-ray spectroscopy and time domain.

Gravitational waves and stalled satellites from massive galaxy mergers at z < 1

Sean McWilliams

Princeton

Tuesday, March 12, 2013

Abstract

Supermassive black holes binaries (SMBHBs) will be the principle source of gravitational waves detectable with pulsar timing arrays (PTAs) at z < 1 and space-based interferometers throughout the observable Universe. Until recently, all estimates of the anticipated signal strength of these sources have relied primarily on simulations to predict the relevant merger rates. I will present results from a completely new approach, which combines observational data and a fully self-consistent numerical evolution of the galaxy mass function. This method, which we will argue is superior to past estimates in several key ways, predicts a merger rate for massive galaxies that is ~10 times larger than that implied by previous calculations. I will explain why previous methods applied to this problem systematically underestimate this merger rate. Finally, I will show that the new rate implies a range of possible gravitational-wave signal strengths that is already in mild tension with PTA observations, with our model predicting a detection at the 95% confidence level as early as 2016. This would make PTAs the first instruments to directly detect gravitational waves, and would provide unprecedented information about the dynamics of merging galaxies, and merging bulges and supermassive black holes within those galaxies. This signal, which is stochastic in nature, may even be strong enough to be detectable at the lowest sensitive frequencies of space-based observatories, depending sensitively on the model parameters as well as the specific detector design and low frequency performance.

Beyond the quantum limit in gravitational wave detectors

Nergis Mavalvala

MIT

Tuesday, March 19, 2013

Abstract

Interferometric gravitational wave detectors are poised to launch a new era of gravitational wave astronomy and unprecedented tests of general relativity. But the sensitivity of second-generation of detectors, currently under construction, is expected to be almost entirely limited by the quantum nature of light. We will explore the quantum limit and describe experimental progress toward circumventing it. These experiments not only lay the foundations for higher sensitivity future detectors, but also serve as testbeds for quantum measurement on unprecedented macroscopic scales.

Recent Kepler Results on Asteroseismology and Exoplanets

Ron Gilliland

STScI Emeritus, Penn State

Tuesday, Mar 26, 2013

Abstract

After nearly four years of operation the NASA Kepler Mission has fostered revolutions in both stellar astrophysics and exoplanets. In this talk I will provide introductions to the results from asteroseismology, and exoplanet studies. Among the more significant legacies of Kepler will be the deep quantitative insight available for selected exoplanet systems through the Kepler data itself providing accurate knowledge of the host stars from asteroseismology, and the planets through coupled knowledge of the transits in Kepler's light curves, and information gleaned from dynamical constraints from either transit timing variations or radial velocity follow-ups. I will emphasize results for systems in which both asteroseismology and detailed transit related studies exist, providing not only excellent knowledge of fundamental parameters for the exoplanets (radius, mass, density), but also obliquity giving insights to formation.

Exoplanetary Science: Instrumentation, Observations, and Expectations

Michael McElwain

GSFC

Thursday, Apr 4, 2013

Abstract

More than 800 exoplanets have been discovered and studied using indirect techniques, leading our field into the exciting new era of comparative exoplanetology. However, the direct detection of exoplanetary systems still remains at the sensitivity limits of both ground- and space-based observatories. The development of new technologies for adaptive optics systems and high contrast instruments continues to increase the ability to directly study exoplanets. The scientific impact of these developments has promising prospects for both short and long timescales. In my talk, I will discuss recent highlights from the SEEDS survey and the current instrumentation in use at the Subaru telescope. SEEDS is a high contrast imaging strategic observing program with 120 nights of time allocated at the NAOJ's flagship optical and infrared telescope. I will also describe new instrumentation I designed to improve the SEEDS capabilities and how a similar techniques could be used for a space-based mission.

The Active South Polar Terrain of Enceladus: How Its Jets, Heat, and Tidal Stresses are Related

Carolyn Porco

Space Science Institute

Tuesday, April 9, 2013

Abstract

In 2005, the Cassini mission at Saturn discovered a remarkable and unique geological province at the south pole of the small moon, Enceladus. Towering jets of powder-sized icy particles, and water vapor laced with organic compounds, vent from several prominent fractures crossing the 500-km wide south polar cap. And a shocking 16GW of thermal radiation emitted by the region, among other lines of evidence, points to a regional sea below the south polar terrain, almost certainly created by the dissipation of tidal energy arising from a 2:1 orbital resonance between Enceladus and its sister moon, Dione. With excess heat, organics, and liquid water, the significance of this moon as a possible host of prebiotic chemistry, or even extraterrestrial organisms, is obvious.

This presentation will examine the relationships between the jets, anomalous heat, and tidal stresses, and evaluate what these relationships mean for the mechanisms responsible for Enceladus' surprising activity.

Probing Molecular Clouds with Observations of Interstellar Hydrides: recent results from Herschel and SOFIA

David Neufeld

JHU

Tuesday, Apr 16, 2013

Abstract

Interstellar hydrides - that is, molecules or molecular ions containing a single heavy element with one or more hydrogen atoms - have proven to be invaluable probes of molecular interstellar material, both in the Milky Way and in distant galaxies. Seven neutral diatomic hydrides have now been observed in the interstellar gas - CH, NH, OH, HF, SiH, SH, and HCl - along with four diatomic hydride cations (CH+, OH+ , SH and HCl+) and several polyatomic species (e.g. CH2, NH2, H2O, H2O+, H2S, H2Cl+, NH3, H3O+). Because the hydrides possess small momenta of inertia relative to molecules that contain two or more heavy atoms, their rotational transitions lie at high frequencies that are often inaccessible from ground-based observatories (at least at z=0, i.e. in the local Universe). Thus, the observational study of interstellar hydrides has benefitted greatly from new capabilities offered by the Herschel Space Observatory and the Stratospheric Observatory for Infrared Astronomy (SOFIA). Because the chemical pathways leading to the formation of interstellar hydrides are fairly simple, the analysis of the observed abundances is relatively straightforward, and provides key information about the physical and chemical conditions within the environments in which hydrides are found. In this presentation, I will review how quantitative measurements of the abundances of hydride molecules have provided important information about several key parameters in the diffuse ISM: the cosmic ray ionization rate, the H2/H ratio, the UV radiation field and the rate of dissipation of interstellar turbulence. Future observations with ALMA promise to extend the diagnostic power of hydride molecules to the high-redshift Universe.

The Most Massive Stars in the Local Universe

Paul Crowther

Sheffield

Tuesday, Apr 23, 2013

Abstract

The lower limit to the mass of stars is well defined, while the upper limit remains controversial. I shall summarise evidence in support of the currently accepted limit, and present recent VLT-based studies of the brightest members of young, nearby star clusters which argue for a higher limit. Consideration is given to questions of binarity using a variety of methods, while we present simulations of star clusters which argue for an upper mass limit close to 300 solar masses. The wider significance of this limit is discussed both for the integrated properties of unresolved star clusters (based on new HST/STIS UV spectroscopy) and the possibility that pair-instability supernovae exist in the local universe, as proposed for SN 2007bi.

Opportunities to test gravity with upcoming large scale structure surveys

Rachel Bean

Cornell

Tuesday, Apr 30, 2013

Abstract

In the search to understand cosmic acceleration a variety of alternatives to Einstein's cosmological constant, including novel matter and modifications to General Relativity, are currently under consideration. We discuss the observational implications of matter and gravity-based dark energy theories and how upcoming cosmological surveys can provide insights into dark energy's nature. In particular we discuss the pivotal roles of upcoming large scale structure surveys measuring weak lensing and redshift space distortions.

Crab pulsar and the nebula: paradigm shifts?

Maxim Lyutikov

Purdue

Tuesday, May 7, 2013

Abstract

We discuss growing evidence that pulsar high energy is emission is generated via Inverse Compton mechanism. We reproduce the broadband spectrum of Crab pulsar, from UV to very high energy gamma-rays - nearly ten decades in energy, within the framework of the cyclotron-self-Compton model. Emission is produced by two counter-streaming beams within the outer gaps, at distances above ~ 20 NS radii. The scattering occurs in the deep Klein-Nishina regime, whereby the IC component provides a direct measurement of particle distribution within the magnetosphere. The required plasma multiplicity is high, ~ 10⁶-10⁷, but is consistent with the average particle flux injected into the pulsar wind nebula. Secondly, recent observations of flares in the Crab nebula call into question the prevalent model of particle acceleration in relativistic astrophysical environments, the stochastic shock acceleration. Magnetic reconnection is likely to play an important, and perhaps a dominant role.

The Universe According to Planck

Charles Lawrence

JPL

Tuesday, May 14, 2013

Abstract

Planck is the third-generation space mission designed to measure the anisotropy of the cosmic microwave background. It has observed the entire sky with unprecedented sensitivity and angular resolution from 30 to 857 GHz. Data from the first 15.5 months were released 21 March 2013. I will discuss scientific results from these data on a range of topics, concentrating on cosmology.

Testing Relativity and Quantum Gravity Using High Energy Astrophysics Observations

Floyd Stecker

GSFC

Tuesday, May 21, 2013

Abstract

As theoretical physics delves deeper into the realm of the ultra-small one of the most fundamental questions is "What is the true nature of space-time?" Is space-time continuous or discontinuous on the smallest scales? Are our speculations concerning the reconciliation of general relativity with quantum mechanics on the right track or are they erroneous? X-ray, gamma-ray and cosmic-ray observations, including those from the Fermi space telescope, are now shedding light on these fundamental questions. I will discuss how various high-energy astrophysics observations are constraining theoretical speculations and quantum gravity models.

Cluster Shadows in the Microwave Sky: Discovering the Most-Massive, Distant Clusters of Galaxies using the South Pole Telescop

Brad Benson

Chicago

Tuesday, June 4, 2013

Abstract

The cosmic microwave background (CMB) is one of our most unique, and powerful, tools to study cosmology. It gives us a snapshot of the content and structure of the Universe at a time only 400,000 years after the Big Bang, while also acting as a backlight to the entire observable Universe - a mechanism that imprints the CMB with signatures of structure formation during its 14 billion year journey. I will discuss recent measurements from the South Pole Telescope (SPT), which has imaged the CMB with an unprecedented combination of depth, area, and resolution. I will give an overview of the SPT cluster survey, a new catalog of ~400 of the most massive, distant clusters in the Universe, and the latest cosmological results from the SPT survey, including: constraints on dark energy, the sum of the neutrino masses, and the number of relativistic particle species. I will also give an overview of the SPT cluster follow-up program and efforts to improve the cluster mass calibration, including large X-ray programs on Chandra and XMM, and a weak lensing program using the Magellan and Hubble telescopes. Finally, I will give the status of plans to equip the SPT with even more sensitive polarization-sensitive instruments, including the currently operating SPTpol and the future SPT-3G experiments. SPTpol and SPT-3G will make high signal-to-noise measurements of the polarization of the CMB, and will additionally expand the SPT cluster survey by over an order of magnitude.