Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session X14: Gravitation and Astrophysics |
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Sponsoring Units: DAP DGRAV Chair: Michela Mapelli, Universita di Padova Room: A226 |
Tuesday, April 17, 2018 10:45AM - 10:57AM |
X14.00001: Post-Newtonian Dynamics in Dense Star Clusters Carl Rodriguez, Pau Amaro-Seoane, Sourav Chatterjee, Frederic Rasio We present models of realistic globular clusters with post-Newtonian dynamics for black holes. By modeling the relativistic accelerations and gravitational-wave emission in isolated binaries and during three- and four-body encounters, we find that nearly half of all binary black hole mergers occur inside the cluster, with about 10\% of those mergers entering the LIGO/Virgo band with eccentricities greater than 0.1. In-cluster mergers lead to the birth of a second generation of black holes with larger masses and high spins, which, depending on the black hole natal spins, can sometimes be retained in the cluster and merge again. As a result, globular clusters can produce merging binaries with detectable spins regardless of the birth spins of black holes formed from massive stars. These second-generation black holes would also populate any upper mass gap created by pair-instability supernovae. [Preview Abstract] |
Tuesday, April 17, 2018 10:57AM - 11:09AM |
X14.00002: Low-mass X-ray binaries from black-hole retaining globular clusters Matthew Giesler, Drew Clausen, Christian Ott Recent studies suggest that globular clusters (GCs) may retain a substantial population of stellar-mass black holes (BHs), in contrast to the long-held belief of a few to zero BHs. We model the population of BH low-mass X-ray binaries (BH-LMXBs), an ideal observable proxy for elusive single BHs, produced from a representative group of Milky Way GCs with variable BH populations. We simulate the formation of BH-binaries in GCs through exchange interactions between binary and single stars in the company of tens to hundreds of BHs. Additionally, we consider the impact of the BH population on the rate of compact binaries undergoing gravitational wave driven mergers. The characteristics of the BH-LMXB population and binary properties are sensitive to the GCs structural parameters as well as its unobservable BH population. We find that GCs retaining $\sim 1000$ BHs produce a galactic population of $\sim 150$ ejected BH-LMXBs whereas GCs retaining only $\sim20$ BHs produce zero ejected BH-LMXBs. Moreover, we explore the possibility that some of the presently known BH-LMXBs might have originated in GCs and identify five candidate systems. [Preview Abstract] |
Tuesday, April 17, 2018 11:09AM - 11:21AM |
X14.00003: Prompt Electromagnetic Transients from Binary Black Hole Mergers Bernard Kelly, John Baker, Zachariah Etienne, Bruno Giacomazzo, Jeremy Schnittman Binary black hole (BBH) mergers provide a prime source for current and future interferometric GW observatories. Massive BBH mergers may often take place in plasma-rich environments, leading to the possibility of a concurrent EM signal observable by traditional astronomical facilities. However, many critical questions about the generation of such counterparts remain unanswered. We explore mechanisms that may drive EM counterparts with magnetohydrodynamical simulations treating a range of scenarios involving equal-mass BH binaries immersed in an initially homogeneous fluid with uniform, orbitally aligned magnetic fields. We find that the time development of Poynting luminosity, which may drive jet-like emissions, is relatively insensitive to aspects of the initial configuration. In particular, over a significant range of initial values, the central magnetic field strength is effectively regulated by the gas flow to yield a Poynting luminosity of $10^{45} - 10^{46} (\rho/10^{-13} {\rm g} \, {\rm cm}^{-3}) M_8^2 {\rm erg} \, {\rm s}^{-1}$. We also calculate the direct plasma synchrotron emissions processed through geodesic ray-tracing. Despite lensing effects and dynamics, we find the observed synchrotron flux varies little leading up to merger. [Preview Abstract] |
Tuesday, April 17, 2018 11:21AM - 11:33AM |
X14.00004: Stellar-Mass Black Hole-Star Binaries and What We Would See Harrison Gott, Dimitry Ayzenberg, Nicolas Yunes When a black hole is illuminated by a light source, its event horizon will cast a shadow because some photons will fall into the black hole and never reach the observer. Typically, the light source one has in mind is an accretion disk that surrounds the black hole, but in principle any light source will produce a shadow. In this talk, I will discuss the possibility of observing a black hole shadow produced by light emitted by a stellar companion. I will present simulated images of these shadows, and calculate the baseline of space telescopes that would be required to observe it. [Preview Abstract] |
Tuesday, April 17, 2018 11:33AM - 11:45AM |
X14.00005: Mode-Tide Interactions in Binary Neutron Stars Xiao Fang, Paulo Montero-Camacho, Christopher Hirata The recent discovery of the binary neutron star (BNS) merger marks the beginning of the multi-messenger astronomy. Similar to black hole mergers, BNSs can also be used as "standard sirens" to measure distances on cosmological scales. However, systematic errors can be introduced when the binary orbit couples to the internal oscillation modes of neutron stars. As the binary move close, the stars will be deformed by the tidal force. Recent studies have discussed the possibility and conditions for generating an instability during the interactions between tides and certain internal oscillation modes, while the physical nature of the instability has not been understood. The presence of this instability would increase the orbital energy dissipation rate, hence affecting the parameter estimation from gravitational wave template fitting. In this talk, I will show our physical understanding of the instability gained from a simplified, analytically-solvable model, and then discuss the effects of magnetic fields. [Preview Abstract] |
Tuesday, April 17, 2018 11:45AM - 11:57AM |
X14.00006: Extended I-Love Relations for Slowly Rotating Neutron Stars Philippe Landry, Jeremie Gagnon-Bischoff, Stephen Green, Nestor Ortiz A neutron star placed in the external gravitational field of a binary companion develops a quadrupole moment due to tidal forces. The induced quadrupole affects the orbital dynamics and imprints on the binary waveform. If the neutron star is spinning, higher multipole moments are also generated from couplings between the spin and the tidal field because of the Einstein equation's nonlinearity. For weak, slowly varying tides and slow rotation, the leading-order rotational-tidal couplings raise an octupole moment. The size of the induced octupole is measured by a rotational-tidal Love number, the analogue of the well-known tidal Love number that characterizes the induced quadrupole. Like the mass and the moment of inertia, both Love numbers are intrinsic properties of the neutron star that depend on its equation of state. Despite this dependence, a certain combination of the moment of inertia and the tidal Love number is known to be virtually equation-of-state independent. We find that so-called I-Love universality also extends to the rotational-tidal Love number: there exists a relation with the moment of inertia that is insensitive to the equation of state. These I-Love relations effectively reduce the number of tidal parameters that enter in the neutron-star binary waveform. [Preview Abstract] |
Tuesday, April 17, 2018 11:57AM - 12:09PM |
X14.00007: I-Love-Q to the extreme Hector O. Silva, Nicolas Yunes Certain bulk properties of neutron stars, like their moment of inertia $I$, rotational quadrupole moment $Q$ and tidal Love number, satisfy approximately universal (equation of state insensitive) relations. But how general are these I-Love-Q relations? Do they continue to hold even when using the most extreme equations of state? In this talk, I will show that these relations do continue to hold even when considering extreme equations of state, constrained only to satisfy a handful of generic, physically-sensible conditions. These results reinforce the robustness of the I-Love-Q relations against our current incomplete picture of physics at supranuclear densities, while strengthening our confidence in the applicability of these relations in neutron star astrophysics. [Preview Abstract] |
Tuesday, April 17, 2018 12:09PM - 12:21PM |
X14.00008: Probing Parity Violation in Neutron Stars: I-Love-Q relations in dynamical Chern Simons Gravity Toral Gupta, Barun Majumder, Kent Yagi, Nicolas Yunes Could gravity be parity-violating? Although General Relativity has passed all tests performed to date, parity invariance has not been tested in the strong field regime. In this talk, I will describe neutron stars in a particular effective field theory that violates parity invariance: dynamical Chern Simons gravity. I will show that the moment of inertia (I), the tidal Love number and the quadrupole moment (Q) continue to satisfy approximately universal (equation of state insensitive) relations, when the dimensional coupling parameter of the theory is properly normalised. These relations can be used to probe parity violation in gravity using future gravitational wave and radio observations with advanced LIGO and SKA respectively, six orders of magnitude more stringently than current solar system bounds. [Preview Abstract] |
Tuesday, April 17, 2018 12:21PM - 12:33PM |
X14.00009: A Framework for Reconstructing the Complete Evolutionary History of Low-Mass X-ray Binaries Charles Kimball, Tassos Fragos, Mads Sorensen, Vicky Kalogera, Aprajita Hajela, Michael Zevin, Slobodan Mentovic We present a methodology for reconstructing the complete evolutionary histories of low-mass x-ray binaries (LMXBs), from Zero Age Main Sequence through Roche-lobe overflow, given observational constraints. Using a patchwork of parametric binary evolution software, model-independent supernova calculations, numerical integration of equations governing tidal evolution, and detailed mass transfer simulations, we obtain constraints on system parameters at birth, the moments just before and just after the core-collapse and supernova of the LMXB’s black hole progenitor, and at the onset of Roche-lobe overflow. In anticipation of the wealth of proper motion data for galactic LMXBs to be provided by upcoming Gaia catalogues, we combine the results with simulated trajectories of the system through the galactic potential to find probable birth sites of the LMXB’s black hole, allowing us to place constraints on the natal kick imparted at supernova. As an example, we apply this framework to GRS 1915+105 and conclude that it did not receive a natal kick in excess of $\sim200$ km/s. [Preview Abstract] |
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