Session E6: Astronomy, Cosmology, Relativity and Gravitation

Spin-Orbit Alignment of Extrasolar Planets as a Probe of their Origin and Evolution

All of our solar system's planets orbit within 7 degrees of the Sun's equatorial plane as a result of their formation in a flat protoplanetary disk with the same direction of angular momentum as the Sun. It turns out, however, that many planets around other stars do NOT orbit in their stars' equatorial planes, a situation known as spin-orbit misalignment. I will discuss how we are able to measure the spin-orbit alignments of stars tens to hundreds of light-years away and how we can use those measurements to figure out how extrasolar planets got to the orbits that they are in today.   

Alfven's Theory of Sunspots and the Emission of Gravitational Waves from the Center of the Sun

The difficulty in detecting gravitational waves with Ligo detectors raises the question for the existence of other sources of gravitational radiation not accessible by these detectors. Gravitational waves are emitted by the motion of large mass quadrupoles, as they are realized in double stars. Large convective mass motions also take place in the center of the sun, but as long as these motions are spherically symmetric they are prevented by Birkhoff's theorem to emit gravitational waves. This is different in Alfven's theory of sunspots where the sun is a magnetohydrodynamic dynamo, which by a theorem of Cowling cannot possess a spherical symmetric convection. With Eddington's mass quadrupole gravitational wave emission formula and the equations for a magnetohydrodynamic dynamo, an upper limit for the emission rate can be established. This estimate is followed by a proposal to detect these waves using the moon as a large Weber bar focusing the waves by Poisson diffraction into the center of the lunar shadow during a total solar eclipse.   

Rotation Measures of diffuse polarized emission: Insights into Galactic magnetism from the Canadian Galactic Plane Survey

The Galactic Magnetic Field (GMF) is a crucial component of the interstellar medium. Not only is it necessary for accelerating cosmic particles and providing pressure balance against gravitational collapse of the Galaxy, it also contributes to star formation and likely played a role in the formation of the Galaxy itself. Studies have shown the large-scale field lines in the Galactic disk to be approximately aligned to the material spiral arms. On a small scale, the field is thought to have a turbulent component, as well as an ordered component that has small-scale variability while being aligned to the large-scale field. However, much remains unknown about the field structure and the study of Galactic magnetism is an active area of research. Novel ways of analyzing currently available data will lead to advances in constructing realistic GMF models. We present a preliminary analysis of Rotation Measures (RMs) of diffuse Galactic synchrotron emission from the Canadian Galactic Plane Survey (CGPS). We show that contrary to the assumption of it being difficult to extract useful information on large-scale structures from RMs of diffuse polarized emission, the CGPS data reveal interesting features worth investigating further and that may provide new insights into the GMF structure.   

Self-Consistent Primordial Helium Abundance Determinations using MCMC

The Primordial Helium Abundance is one of the fundamental products of the early Universe and, therefore, offers a unique window into the content and interactions of the Universe only several minutes after the Big Bang. Using measurements from the Cosmic Microwave Background, Big Bang Nucleosynthesis now predicts the initial elemental composition of the universe with high precision. However, recent observational determinations based on spectral observations of H II regions are complicated by systematic effects and do not show complete agreement with each other, or with the CMB prediction. I will discuss recent improvements in these determinations, with particular emphasis on correctly capturing the uncertainty in the result. These will include expanding and updating the physical model, improving self-consistency, introducing Markov Chain Monte Carlo to facilitate rigorous statistical treatment of the uncertainty, and extracting a reliable dataset from recent observations. Discussion of the results will highlight gains made in the reliability and precision of the Primordial Helium Abundance as well as limitations arising from systematic effects and model degeneracies.   

Accretion of The Magnetized Neutrino-cooled Torus on a Rotating Black Hole

Neutrino-cooled accretion flow around a black hole, produced by a compact binary merger, is a promising scenario for a short duration gamma ray burst central engine. The turbulence caused by magneto-rotational instability is expected to play an important role in driving accretion and thermal equilibrium of the disk. We study the magnetically-driven post-merger evolution of a black hole-neutron star binary system using results from a previous simulation and Einsteins Spectral Codes MHD module. We mostly focus on studying the effects of neutrino cooling and magnetic filed on the structure of the disk and neutrino emission and neutrino-antineutrino energy deposition of the disk.   

A high order accurate finite difference scheme with boundary closures for astrophysical simulations

In black hole simulations it is difficult to maintain high order accuracy for fluid evolutions in regions near excision inner-boundaries of the horizon, where many methods do not capture accurate information from the matter inflow of black hole-neutron star binary evolutions and other accretion type problems. With a multipatch Energy Stable Weighted Essentially non-Oscillatory (ESWENO) scheme, high order accuracy between patch interfaces and on domain data boundaries can be ensured for the hydrodynamic variables. We present preliminary results of a working multipatch ESWENO, focusing on multidimensional shock capture and applications for black hole accretion disk simulations.   

Probing Physics with Observations of Neutron Stars and White Dwarfs

White dwarfs and neutron stars are two of the densest objects in the Universe. Discovered 105 and 45 years ago, these objects are two of the best astrophysical laboratories of fundamental physics. The simple existence of white dwarfs is a stellar-size manifestation of quantum physics. I will describe how we use these objects today to study quantum-chromodynamics, quantum-electrodynamics, neutrino and axion physics and even thermodynamics in realms inaccessible to Earth-bound laboratories. In the process we also discover the detailed fate of our own Earth and Sun.   

Experimental highlights and challenges in Advanced LIGO

In the past years, the advanced LIGO project made a significant amount of progress. Recently, both of the laser interferometers successfully achieved full resonance and demonstrated stable operation for more than two hours. The project is now preparing for observation runs by reducing various noises and improving the duty cycle. Since the aLIGO interferometer employs a large number of active control systems and a complicated interferometric configuration, the process of optimizing the control loops and reducing noise coupling/sources is not always straightforward. In fact, this is the point where most of the experimental challenges lie. In this talk, I will present some of the challenges and how we are addressing them.   

Estimation of aligned search efficiency for low-mass coalescing generic spinning binary black holes in gravitational wave data

In this work, we study the efficiency of the aligned spin search for the gravitational waves from coalescing binary black holes of mass $M_{\mathrm{total}} \in [4,16]M_\odot $ having generic spin where the spin angular momenta of the binary black holes is not specifically (anti-)aligned with the orbital angular momentum of the system. The simulated gravitational wave signals from generic spinning binary black holes are injected to real detector noise of initial LIGO era as well as to the simulated realistic noise for early advanced LIGO. We have done a comparative study between the recovery of such generic-spinning signals with aligned spin template bank and non-spinning \textit{TaylorF2} template bank using \textit{gstlal} search pipeline . The aligned spinning template bank is generated by the \textit{TaylorF2RedSpin} waveform family that comprises two mass parameters and one reduced spin parameter. We construct our template bank by following stochastic template placement algorithm. The performance of the reduced spin stochastic template bank has been assessed towards both aligned and precessional low mass binary black hole systems using two weeks of initial LIGO S5 data and simulated early advanced LIGO data.   

Improving LIGO Data Quality By Detecting Artifacts Arising from Bilinear and Nonlinear Noise Couplings

In this work, we describe tools developed for detecting artifacts in the gravitational wave (GW) channel of the Laser Interferometer Gravitational-wave Detector (LIGO) arising from bilinear and nonlinear noise couplings. Such artifacts reduce the sensitivity of searches for transient GW signals, e.g., from compact binary coalescences (CBCs), by increasing their false-alarm rates. Once detected, the noise sources must be identified, with the objective of either removing them or handling them in a way that mitigates their adverse effect on data quality. We recently updated these tools for Advanced LIGO (aLIGO) data analysis and successfully applied it to the last engineering run ``ER6'' data. We describe here some of the higher order noise couplings found in that data and steps underway to understand their sources.   

Acoustic Franz Wave Scattering From Circular Cylinders

Previous acoustic research on backscattering from cylinders partially-exposed at an air/water interface revealed a scattering feature at low exposures and grazing angles that did not correspond to either specular (direct) reflection or any other previously-studied acoustic scattering feature. Franz waves, which have speed less than the speed of sound in water, and which can follow the curved surface of the cylinder, were identified as the likely source of this feature. An exact solution available for a half-exposed cylinder, when converted from the frequency to the time domain for different grazing angles, shows three features that have the expected timing of Franz waves. These three different features correspond to three different Franz paths, which differ in the number of times they reflect off the air/water interface. Further experiments showed Franz scattering features at various exposures and grazing angles, at both air/water and sand/water interfaces.   

Gravitational wave detectors for the coming decades

After the first few detections of gravitational waves, the scientific community will want more frequent detections, with higher signal to noise ratios to answer some of the pressing scientific questions that will become available with this new observational tool. This talk will focus on two promising ways of improving the sensitivity of gravitational wave detectors, both of which rely on proven technologies to provide significant scientific gains. In the next several years, squeezed states can be injected into the existing detectors to reduce the quantum noise which limits their design sensitivity at most frequencies in their detection band. In the longer term, extending the length of the interferometer arms may be the most practical and powerful way to further improve the sensitivity and allow for observation of gravitational waves at cosmological distances.