Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session T09: Compact Object Mergers: Black Holes & Neutron StarsLive
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Sponsoring Units: DAP Chair: Matt Caplan, ISU |
Monday, April 19, 2021 3:45PM - 3:57PM Live |
T09.00001: The Landscape of Disk Outflows From Black Hole - Neutron Star Mergers Rodrigo Fernandez, Francois Foucart, Jonas Lippuner Mass ejection from accretion disks formed in mergers of black holes (BHs) and neutron stars (NSs) is a significant contributor to the production of r-process elements and to the kilonova transient. However, there has been a limited exploration of the broad parameter space of disk outflows, which becomes relevant given the event rate of O3 and the lack of any detected electromagnetic counterparts. I'll report the results of 27 high-resolution, axisymmetric, long-term viscous hydrodynamic simulations of post-merger BH accretion disks that include neutrino emission/absorption and post-processing with a nuclear reaction network. We characterize the dependence of the fraction of the disk mass ejected on disk compactness (BH mass over initial disk radius) and on the disk mass at fixed compactness. The radioactive luminosity from the disk outflow alone available to power kilonovae spans two orders of magnitude over the BH-NS parameter space. For most plausible binary configurations, this disk contribution is well below the kilonova mass upper limits for GW190814. [Preview Abstract] |
Monday, April 19, 2021 3:57PM - 4:09PM Live |
T09.00002: GRMHD simulations of binary BH-NS and NS-NS mergers: Progenitors of short-gamma ray bursts Milton Ruiz, Antonios Tsokaros, Stuart Shapiro Binary black hole-neutron star (BHNS) and neutron star-neutron star (NSNS) mergers are not only important sources of gravitational waves, but also promising candidates for coincident electromagnetic counterparts emission. Here we summarize recent simulations in general relativistic magnetohydrodynamics (GRMHD) designed to establish BHNS and NSNS mergers as viable progenitors of the central engines that power short gamma--ray bursts (sGRBs) and thereby solidify their role as multimessenger sources. We survey binaries that differ in their configuration of the seed magnetic field, mass-ratio, and spin of the NS or BH. We find that by $\Delta t > 50$ms after the peak gravitational wave signal an incipient jet is launched when: 1) the seed magnetic field has a sufficiently large-scale poloidal component along the total angular momentum of the system, 2) the mass ratio in BHNSs is not far from unity 3) the initial spin of the BH in BHNSs is larger than $\sim 0.5$. 4) the NSNS remnant is a hypermassive NS that undergoes delayed collapse. We do not find a strong correlation between jet launching and the spin of the NS. The lifetime and Poynting luminosities of the jet are consistent with typical sGRBs, as well as with the Blandford--Znajek mechanism for launching jets. [Preview Abstract] |
Monday, April 19, 2021 4:09PM - 4:21PM Live |
T09.00003: High-energy neutrino and electromagnetic counterparts of post-merger jets from super massive black hole mergers Chengchao Yuan, Kohta Murase, Shigeo Kimura, Theodore B. Zhang, Peter Meszaros Supermassive black hole (SMBH) coalescences are ubiquitous in the history of the Universe and often exhibit strong accretion activities and powerful jets. These SMBH mergers are also promising candidates for future gravitational wave detectors such as Laser Space Inteferometric Antenna (LISA). In this work, we consider neutrino and electromagnetic counterpart emissions originating from the jet-induced shocks. We formulate the jet structures and relevant interactions therein, and then evaluate neutrino emission from each shock site. We find that month-to-year high-energy neutrino emission from the postmerger jet after the gravitational wave event is detectable by IceCube-Gen2 within approximately five to ten years of operation in optimistic cases where the cosmic-ray loading is sufficiently high and a mildly super-Eddington accretion is achieved. In addition, based on our model that predicts slowly fading transients with durations of $\sim1-10$ months with a time delay from days to months after the coalescence, we discuss implications for EM follow-up observations after the GW detection. [Preview Abstract] |
Monday, April 19, 2021 4:21PM - 4:33PM Live |
T09.00004: Threshold Mass for Prompt Blackhole Formation From Binary Neutron Star Mergers Rahul Kashyap, Abhishek Kumar, Surendra Padmata, Aviral Prakash, David Radice Binary neutron star (BNS) mergers are one of the most violent events in our universe and one of the most important sources in current and future gravitational wave (GW) observatories. Observables from these events reveal properties of supranuclear matter inaccessible to any experiments yet possible on the Earth. There is widespread understanding that mergers result into either a blackhole with an accretion disk or, a differentially rotating massive neutron star. The boundary between these two outcomes as a function of BNSs provides us information about the dynamics of dense matter i.e. equation of state (EOS). We perform a series of simulation using the numerical relativity code Whisky-THC for a range of equation of state to find the threshold value for total mass beyond which system collapses to blackhole promptly without any oscillations. We then compare our result in the literature and comment on EOS-independent relationship for prediction of threshold masses. Such information when compared with future GW will give us unique probes to understand dynamical properties of matter at and above nuclear density. [Preview Abstract] |
Monday, April 19, 2021 4:33PM - 4:45PM Live |
T09.00005: Binary Neutron Star Impostors & Event GW190814 Antonios Tsokaros, Milton Ruiz, Stuart Shapiro, Lunan Sun, Koji Uryu In the first part of this talk I will address the following question: can we distinguish a binary black hole undergoing a merger from a binary neutron star if the individual compact companions have masses that fall inside the so-called mass gap of $3-5\ M_\odot$? For neutron stars, achieving such masses typically requires extreme compactness. I therefore will present general relativistic initial data and evolution simulations of binary neutron stars-the impostors- initially in quasiequilibrium circular orbits and supported by an EOS near the causal limit that exhibit extreme compactness. I will compare their gravitational waveforms with those of merging black hole binaries of the same mass. In the second part I will discuss event GW190814 of a merging binary having a $\sim 23 M_\odot$ black hole and a $\sim 2.6 M_\odot$ compact companion. I will explore some consequences of the assumption that the secondary was a neutron star. [Preview Abstract] |
Monday, April 19, 2021 4:45PM - 4:57PM Live |
T09.00006: General-relativistic simulations of quasi-circular inspirals of charged black holes Gabriele Bozzola, Vasileios Paschalidis The electric charge is a parameter often neglected in general-relativistic simulations of black holes. As a result, little is known about the dynamics of charged binary black holes in the latest stages of their inspiral. In this talk, we present our first numerical-relativity simulations of quasi-circular mergers of these systems. Using a $3+1$ formalism, we obtained fully self-consistent solutions of Einstein-Maxwell's equations, and extracted the electromagnetic and gravitational output. We will discuss what GW150914 can teach us about the charge of astrophysical black holes and fundamental physics in light of our new simulations. [Preview Abstract] |
Monday, April 19, 2021 4:57PM - 5:09PM Live |
T09.00007: Parameter Estimation of Eccentric Systems Eamonn O'Shea, Prayush Kumar Current LIGO/Virgo search and parameter estimation pipelines have yet to identify a candidate binary black hole coalescence with appreciable eccentricity. However, simulations of dense stellar environments suggest that 10\% of binary black holes will enter the LIGO/Virgo band which eccentricity greater than 0.1. Given that, going forward, we should expect LIGO/Virgo - and future detectors - to begin detecting gravitational wave signals from eccentric binaries, it is important to identify the challenges these systems may pose for existing parameter estimation pipelines. To this end, we perform an injection study of eccentric binary black hole mergers to identify how well existing pipelines and waveform models can recover the source parameters. In particular, we identify a systematic bias in the estimation of the masses of the binary black holes when the system has moderate eccentricity. [Preview Abstract] |
Monday, April 19, 2021 5:09PM - 5:21PM Live |
T09.00008: Gravitational wave echoes from compact binary coalescence Sizheng Ma, Yanbei Chen It is suggested that delayed and repeating gravitational wave echoes, following gravitational waves emitted by compact binary coalescence, can be produced if the binary contains Exotic Compact Objects (ECOs) that mimic black holes, or if there are near-horizon quantum structures surrounding black holes. If gravitational wave echoes exist, they will serve as an important tool to study the physics of black holes or exotic compact objects.~ We present an echo waveform model, based on inspiral-merger-ringdown waveforms computed from numerical relativity (reproduced by NR surrogate models), and linear perturbation theory of the final spinning compact object. In constructing this model, we divide the compact binary coalescence spacetime into a strong field region, and a "weak field region" in which linear perturbation theory of a Kerr spacetime applies.~ The echoes we construct arise from the weak-field region, hence incorporate those generated from reflections from the near-horizon region of the final compact object. Our model is parametrized by the ECO's reflectivity, as well as the location of the interface between the strong- and weak-field regions. We also discuss the detectability of echoes with current and future detectors. [Preview Abstract] |
Monday, April 19, 2021 5:21PM - 5:33PM Live |
T09.00009: Black Hole Formation in the Lower Mass Gap through Mergers and Accretion in AGN Disks Yang Yang The heaviest neutron stars and lightest black holes expected to be produced by stellar evolution leave the mass-range $2.2$\,M$_{\odot}\lesssim m \lesssim 5$\,M$_\odot$ largely unpopulated. Objects found in this so-called {\it lower mass gap} likely originate from a distinct astrophysical process. Such an object, with mass $2.6$\,M$_\odot$ was recently detected in the binary merger GW190814 through gravitational waves by LIGO/Virgo. Here we show that black holes in the mass gap are naturally assembled through mergers and accretion in AGN disks, and can subsequently participate in additional mergers. We compute the properties of AGN-assisted mergers involving neutron stars and black holes, accounting for accretion. We find that mergers in which one of the objects is in the lower mass gap represent up to $4$\% of AGN-assisted mergers detectable by LIGO/Virgo. The lighter object of GW190814, with mass $2.6$\,M$_\odot$, could have grown in an AGN disk through accretion. We find that the unexpectedly high total mass of 3.4\,M$_\odot$ observed in the neutron star merger GW190425 may also be due to accretion in an AGN disk. [Preview Abstract] |
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