Bulletin of the American Physical Society
83rd Annual Meeting of the APS Southeastern Section
Volume 61, Number 19
Thursday–Saturday, November 10–12, 2016; Charlottesville, Virginia
Session M1: Gravity in Astrophysics |
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Chair: Scott Ransom, NRAO, University of Virginia Room: West Ballroom |
Saturday, November 12, 2016 10:45AM - 10:57AM |
M1.00001: Pulsar Timing Arrays Beyond the Isotropic Stochastic GW Background Dustin Madison Long-standing models for the nanohertz gravitational wave (GW) stochastic background are increasingly in tension with current pulsar timing array (PTA) constraints. As such, supermassive black hole binaries may be driven to merger more quickly than previously thought, eccentricity may play an integral role in binary black hole evolution, and unconventional sources of GWs may prove key to an initial GW detection by PTAs. I will discuss developing efforts to detect a more astrophysically realistic stochastic background and recent efforts to detect localized burst-like sources of GWs using PTAs. I will discuss near-future prospects for improving PTA sensitivity to GWs. [Preview Abstract] |
Saturday, November 12, 2016 10:57AM - 11:09AM |
M1.00002: Probing Neutron Star Physics with NANOGrav and Other Millisecond Pulsars H. Thankful Cromartie The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) times $\sim$50 millisecond pulsars (MSPs) scattered across the sky in order to detect an isotropic, stochastic background of gravitational waves at very low frequencies. Of the MSPs in this pulsar timing array, 24 have binary companions, and 14 were found to display significant Shapiro delay. Measurements of this general relativistic effect (in addition to standard parameters gleaned from pulsar timing) yield the systems' inclination angles and masses of both the companion star and the pulsar. While companion masses and inclination angles can be important clues in understanding binary evolution, pulsar mass measurements are absolutely critical for understanding the neutron star equation of state and mass-radius relationship. Recent Shapiro delay measurements have strongly constrained physics at hyper-nuclear densities, and planned observations of more intriguing systems could help further illuminate the mysterious nature of pulsar interiors. [Preview Abstract] |
Saturday, November 12, 2016 11:09AM - 11:21AM |
M1.00003: Large scale data analysis in pursuit of gravitational waves Vladimir Dergachev Continuous gravitational waves are expected to be emitted by rotating neutron stars. Because CW amplitudes are thought to be extremely weak, long time integrations must be carried out. With the sources described by multi-dimensional parameter spaces, such searches are computationally limited. We will discuss how large computer clusters are used to search for such sources and describe mathematically rigorous algorithms used to deal with non-Gaussian data and detector artifacts. [Preview Abstract] |
Saturday, November 12, 2016 11:21AM - 11:33AM |
M1.00004: Measurement of Quasi Normal Modes for a population of Binary Black Hole Mergers Carlos Filipe Da Silva Costa, Sergey Klimenko, Shubhanshu Tiwari Perturbed solutions of the Kerr Black Hole (BH) are superimposition of damped sinusoids, named Quasi Normal Modes (QNM). These modes are completely defined by the final black hole parameters, mass and spin. Numerical simulations support that Binary BHs (BBH), after merging, produce a final BH emitting gravitational waves as described by the QNMs. This signal is very weak and hence the extraction of a QNM is quite challenging for the current generation of the ground based detectors. I will present a method for extraction of superimposed QNMs from future multiple observations of BBH merger signals in the advanced interferometers. We show that we can coherently sum up QNMs from the different signals and measure QNM parameters to prove the Kerr nature of a detected BHs population. [Preview Abstract] |
Saturday, November 12, 2016 11:33AM - 11:45AM |
M1.00005: Submillimeter water megamasers in nearby AGNs Dominic Pesce, James Braatz, Violette Impellizzeri Water megamasers at 22 GHz (1.3 cm) have been detected in the nuclei of about 150 galaxies, where they are observed to arise from either the parsec-scale accretion disk or gas outflows associated with the AGN. Now, with the sensitivity and spatial resolution of ALMA, detailed studies of \textit{submillimeter}-wavelength water megamasers in AGNs are possible for the first time. Observations of these megamasers will complement and expand on the rich observations of 22 GHz systems that have, until now, provided the only means to map molecular gas in AGNs directly on sub-parsec scales. Recent detections of 321 GHz megamaser activity in several nearby AGNs have shown that the sub-mm masers are tentatively associated with the circumnuclear accretion disk, and in at least one case (that of the Circinus galaxy) they may also trace the accretion disk at radii interior to their 22 GHz counterparts. Future long-baseline observations of this maser system will spatially resolve the maser distribution. If they can be widely detected, observations of these and other submillimeter lines will greatly increase the power of megamasers to measure black hole masses, distances, and physical conditions in accretion disks. [Preview Abstract] |
Saturday, November 12, 2016 11:45AM - 11:57AM |
M1.00006: Heuristic Derivation of Black Hole Properties Using Dimensional Analysis Kale Oyedeji, Ronald Mickens Black holes have many interesting and non-obvious properties. The precise details of the features of standard black holes (i.e., those without charge or spin) generally requires calculational techniques involving general relativity, quantum mechanics, thermodynamics, etc. [1]. We demonstrate that many, if not all, of the important aspects of black holes may be estimated, up to a pure number proportionality constant, by the appropriate application of the method of dimensional analysis [2]. In particular, for a black hole having mass M, we ``calculate'' its radius, surface area, density, temperature, and life-time.\\ \\$[1]$ M. Blecher, General Relativity (World Scientific, Singapore, 2016) [2] H.E. Huntley, Dimensional Analysis (Dover, New York, 1967). [Preview Abstract] |
Saturday, November 12, 2016 11:57AM - 12:09PM |
M1.00007: The Viability of Phantom Dark Energy as a Quantum Field in 1st-Order FLRW Space Kevin Ludwick In the standard cosmological framework of the 0th-order FLRW metric and the use of perfect fluids in the stress-energy tensor, dark energy with an equation-of-state parameter $w < -1$ (known as phantom dark energy) implies negative kinetic energy and vacuum instability when modeled as a scalar field. However, the accepted values for present-day $w$ from Planck and WMAP9 include a significant range of values less than $-1$. We consider a more accurate description of the universe through the 1st-order perturbing of the isotropic and homogeneous FLRW metric and the components of the stress-energy tensor and investigate whether a field with an apparent $w<-1$ may still have positive kinetic energy. Treating dark energy as a classical scalar field in this metric, we find that it is not as obvious as one might think that phantom dark energy has negative kinetic energy categorically. Analogously, we find that field models of quintessence dark energy ($w>-1$) do not necessarily have positive kinetic energy categorically. We then investigate the same question treating dark energy as a quantum field in 1st-order FLRW space-time and examining the expectation value of the stress-energy tensor for $w<-1$ using adiabatic expansion. [Preview Abstract] |
Saturday, November 12, 2016 12:09PM - 12:21PM |
M1.00008: Conservative Transformation Group: Geometry of the Quantum? Edward Green An enlargement of the covariance group of general relativity which may unify the known forces has been developed by Pandres. Using tetrads on a four-dimensional space, this new transformation group, called the conservation group, contains the group of diffeomorphisms as a proper subgroup. The fundamental geometric object of the new geometry is the curvature vector, $C_\mu$ and the corresponding Lagrangian density is $C^\mu C_\mu \sqrt{-g}$. We find that the field equations are covariant under the larger group. A source Lagrangian term which produces a stress-energy tensor which is also covariant under the conservation group is given and means for fixing the gauge in a covariant way are discussed. Thus, one may find a solution of the field equations which satisfies given boundary conditions, and this determines a family of manifolds. As this family preserves the stress-energy of the source, but not the associated stress-energy of the free field, an energy condition is needed to determine the classical manifold. We conjecture that the required energy condition involves the scalar curvature, $R$. [Preview Abstract] |
Saturday, November 12, 2016 12:21PM - 12:33PM |
M1.00009: Geometry of the Conservative Transformation Group: Reformulation of a covariant derivative for tensors, spin tensors and spinors and a theory of mass. Edward Green An enlargement of the covariance group of general relativity which may unify the known forces has been developed by Pandres. Using tetrads on a four-dimensional space, this new transformation group, called the conservation group, contains the group of diffeomorphisms as a proper subgroup. With this extension there arises a need for reformulating appropriate covariant derivatives of tensors, spin tensors and spinors. We develop this extension which we call the stroke derivative and compare our connections to those of the usual spin covariant derivative and spinor covariant derivative. We also exhibit a natural way to introduce mass and show that mass is invariant under the group of conservative transformations. [Preview Abstract] |
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