A5029559893- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Astrophysics and Cosmic Phenomena
- Solar and Space Plasma Dynamics
- Ionosphere and magnetosphere dynamics
- Gamma-ray bursts and supernovae
- Radio Astronomy Observations and Technology
- Laser-Plasma Interactions and Diagnostics
- Particle Accelerators and Free-Electron Lasers
- Astrophysics and Star Formation Studies
- Magnetic confinement fusion research
- High-pressure geophysics and materials
- Geophysics and Gravity Measurements
- Geomagnetism and Paleomagnetism Studies
- Cosmology and Gravitation Theories
- Relativity and Gravitational Theory
- Astro and Planetary Science
- Stellar, planetary, and galactic studies
- Geophysics and Sensor Technology
- Mechanics and Biomechanics Studies
- Galaxies: Formation, Evolution, Phenomena
- Dust and Plasma Wave Phenomena
- Black Holes and Theoretical Physics
- Adaptive optics and wavefront sensing
- Astronomical Observations and Instrumentation
Canadian Institute for Theoretical Astrophysics
2023-2025
University of Toronto
2023-2025
Perimeter Institute
2023-2025
Netherlands Institute for Radio Astronomy
2025
Flatiron Institute
2018-2024
Princeton University
2018-2024
Institute for Advanced Study
2023-2024
Flatiron Health (United States)
2018-2024
Albert Einstein College of Medicine
2023-2024
Space Telescope Science Institute
2024
Abstract Magnetic reconnection can power bright, rapid flares originating from the inner magnetosphere of accreting black holes. We conduct extremely high-resolution (5376 × 2304 cells) general-relativistic magnetohydrodynamics simulations, capturing plasmoid-mediated in a 3D magnetically arrested disk for first time. show that an equatorial, plasmoid-unstable current sheet forms transient, nonaxisymmetric, low-density within few Schwarzschild radii. flux bundles escape event horizon through...
The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in Galactic Center on 2017 April 5-11 1.3 millimeter wavelength band. At same time, interferometric array data from Atacama Large Millimeter/submillimeter Array and Submillimeter were collected, providing Sgr light curves simultaneous with EHT observations. These sets, complementing very-long-baseline interferometry, are characterized by a cadence signal-to-noise ratio previously unattainable for at...
We compare relativistic particle integrators commonly used in plasma physics showing several test cases relevant for astrophysics. Three explicit pushers are considered, namely the Boris, Vay, and Higuera-Cary schemes. also present a new fully implicit integrator that is energy conserving. Furthermore, method based on guiding center approximation included. The algorithms described such they can be readily implemented magnetohydrodynamics codes or Particle-in-Cell codes. Our comparison...
The no-hair theorem of general relativity states that isolated black holes are characterized by three parameters: mass, spin, and charge. In this Letter we consider Kerr endowed with highly magnetized plasma-filled magnetospheres. Using relativistic kinetic plasma resistive magnetohydrodynamics simulations, show a dipole magnetic field on the event horizon opens into split-monopole reconnects in plasmoid-unstable current-sheet. is satisfied, sense all components stress-energy tensor decay...
We report measurements of the gravitationally lensed secondary image -- first in an infinite series so-called "photon rings" around supermassive black hole M87* via simultaneous modeling and imaging 2017 Event Horizon Telescope (EHT) observations. The inferred ring size remains constant across seven days EHT observing campaign is consistent with theoretical expectations, providing clear evidence that such probe spacetime a striking confirmation models underlying set results. residual diffuse...
Abstract Active galactic nuclei in general, and the supermassive black hole M87 particular, show bright rapid gamma-ray flares up to energies of 100 GeV above. For M87, multiwavelength components, variability timescale is comparable dynamical time event horizon, suggesting that emission may come from a compact region near nucleus. However, mechanism for these not well understood. Recent high-resolution general-relativistic magnetohydrodynamic simulations occurrence episodic magnetic...
We study the accretion of collisionless plasma onto a rotating black hole from first principles using axisymmetric general-relativistic particle-in-cell simulations. carry out side-by-side comparison these results to analogous magnetohydrodynamic Although there are many similarities in overall flow dynamics, three key differences between kinetic and fluid simulations identified. Magnetic reconnection is more efficient, rapidly accelerates nonthermal particle population, our approach. In...
ABSTRACT The nature of cosmic ray (CR) transport in the Milky Way remains elusive. predictions current microphysical CR models magnetohydrodynamic (MHD) turbulence are drastically different from what is observed. These usually focus on MHD with a strong guide field and ignore impact turbulent intermittency particle propagation. This motivates our studying alternative regime large-amplitude δB/B0 ≫ 1, which intermittent small-scale magnetic reversals ubiquitous. We study such by integrating...
Binaries containing a compact object orbiting supermassive black hole are thought to be precursors of gravitational wave events, but their identification has been extremely challenging. Here, we report quasi-periodic variability in x-ray absorption, which interpret as outflows (QPOuts) from previously low-luminosity active galactic nucleus after an outburst, likely caused by stellar tidal disruption. We rule out several models based on observed properties and instead show using general...
Abstract The Event Horizon Telescope Collaboration (EHTC) observed the Galactic centre source Sagittarius A* (Sgr A*) and used emission models primarily based on single ion temperature (1T) general relativistic magnetohydrodynamic (GRMHD) simulations. This predicted is strongly dependent a modelled prescription of ion-to-electron ratio. most promising are magnetically arrested disk (MAD) states. However, nearly all MAD exhibit larger temporal fluctuations in radiative 230 GHz compared to...
Abstract Supermassive binary black holes in galactic centers are potential multimessenger sources gravitational waves and electromagnetic radiation. To find such objects, isolating unique signatures of their accretion flow is key. With the aid three-dimensional general-relativistic magnetohydrodynamic simulations that utilize an approximate, semianalytic, superimposed spacetime metric, we identify two for merging binaries. Both involve magnetic reconnection analogous to plasma processes...
The Event Horizon Telescope (EHT) Collaboration has recently produced the first resolved images of central supermassive black hole in giant elliptical galaxy M87. Here we report on tests consistency and accuracy general relativistic radiative transfer codes used within collaboration to model M87* Sgr A*. We compare evaluate (1) deflection angles for equatorial null geodesics a Kerr spacetime; (2) calculated from series simple, parameterized matter distributions metric using simplified...
We investigate whether photon ring observations in black hole imaging are able to distinguish between the Kerr general relativity and alternative holes that deviate from Kerr. Certain aspects of rings have been argued be robust observables Very-Long-Baseline Interferometry (VLBI) which carry imprints underlying spacetime. The shape, as well its Lyapunov exponent (which encodes narrowing successive subrings), detailed probes geometry; measurements thereof provide a strong null test metric....
Abstract The origins of the various outbursts hard X-rays from magnetars (highly magnetized neutron stars) are still unknown. We identify instabilities in relativistic magnetospheres that can explain a range X-ray flare luminosities. Crustal surface motions twist magnetar magnetosphere by shifting frozen-in footpoints magnetic field lines current-carrying flux bundles. Axisymmetric (2D) exhibit strong eruptive dynamics, i.e., catastrophic lateral triggered critical footpoint displacement ψ...
Abstract We perform the first magnetohydrodynamic simulation tracking magnetosphere of a collapsing magnetar. The collapse is expected for massive rotating magnetars formed in merger events and may occur many hours after merger. Our suggests novel mechanism gamma-ray burst (GRB), which uncollimated forms delayed high-energy counterpart gravitational waves. shows that launches an outgoing magnetospheric shock, hot magnetized outflow behind shock. baryon free uncollimated, its power peaks on...
Abstract We study the magnetospheric evolution of a nonaccreting spinning black hole (BH) with an initially inclined split monopole magnetic field by means 3D general relativistic magnetohydrodynamic simulations. This serves as model for neutron star (NS) collapse or BH–NS merger remnant after inherited magnetosphere has settled into creating striped wind. show that monopolar current sheet aligns over time BH equatorial plane. The inclination angle evolves exponentially toward alignment,...
Abstract Hot spots, or plasmoids, which form due to magnetic reconnection in current sheets, are conjectured power frequent X-ray and near-infrared flares from Sgr A*, the black hole center of our Galaxy. It is unclear how, where, when sheets accretion disks. We perform axisymmetric general-relativistic resistive magnetohydrodynamics simulations model plasmoid formation a range flows. Current plasmoids ubiquitous features that regardless initial field disk, magnetization quasisteady-state...
We apply the general relativistic resistive magnetohydrodynamics code bhac to perform a 2D study of formation and evolution reconnection layer in between two merging magnetic flux tubes Minkowski space–time. Small-scale effects regime low resistivity most relevant for dilute astrophysical plasmas are resolved with very high accuracy due extreme resolutions obtained adaptive mesh refinement. Numerical convergence highly non-linear plasmoid-dominated is confirmed sweep resolutions. employ both...
We study the physical properties of four-dimensional, string-theoretical, horizonless "fuzzball" geometries by imaging their shadows. Their microstructure traps light rays straying near would-be horizon on long-lived, highly redshifted chaotic orbits. In fuzzballs sufficiently scaling limit this creates a shadow much like that black hole, while avoiding paradoxes associated with an event horizon. Observations size and residual glow can potentially discriminate between away from alternative...
The processes controlling the complex clump structure, phase distribution, and magnetic field geometry that develops across a broad range of scales in turbulent interstellar medium remains unclear. Using unprecedentedly high resolution three-dimensional magnetohydrodynamic simulations thermally unstable systems, we show large current sheets to plasmoid-mediated reconnection form regularly throughout volume. plasmoids three distinct environments: (i) within cold clumps, (ii) at asymmetric...
Abstract Supermassive black holes in active galactic nuclei are known to launch relativistic jets, which observed across the entire electromagnetic spectrum and thought be efficient particle accelerators. Their primary radiation mechanism for radio emission is polarized synchrotron produced by a population of nonthermal electrons. In this Letter, we present global general magnetohydrodynamical (GRMHD) simulation magnetically arrested disk (MAD). After reaches MAD state, show that waves...
This article uses magnetic Rayleigh-Taylor instability in relativistic collisionless plasma as an example of astrophysical process for nonthermal particle acceleration, and uncover the onset large-scale plumes formed by accumulation small ones via particle-in-cell simulations. is posed a potential mechanism flares.
Context. The nearby elliptical galaxy M87 contains one of only two supermassive black holes whose emission surrounding the event horizon has been imaged by Event Horizon Telescope (EHT). In 2018, more than dozen multi-wavelength (MWL) facilities (from radio to γ -ray energies) took part in second EHT campaign. Aims. goal this extensive MWL campaign was better understand physics accreting hole M87*, relationship between inflow and inner jets, high-energy particle acceleration. Understanding...
ABSTRACT In general relativistic magnetohydrodynamic (GRMHD) simulations, accreted magnetic flux on the black hole horizon episodically decays, during which reconnection heats up plasma near horizon, potentially powering high-energy flares like those observed in M87* and Sgr A*. We study mm observational counterparts of such flaring episodes very high resolution GRMHD simulations. The change 230 GHz expected energy depends primarily efficiency accelerating γ ≳ 100 (Te 1011 K) electrons. For...
We propose the tracing of motion a shearing hot spot near Sgr A* source through dynamical image reconstruction algorithm, StarWarps. Such may form as exhaust magnetic reconnection in current sheet black hole horizon. A that is ejected from into an orbit accretion disk shear and diffuse due to instabilities at its boundary during orbit, resulting distinct signature. subdivide two different phases: first phase refers appearance modeled bright blob, followed by subsequent phase. employ...