Antonios Nathanail

Antonios Nathanail
Goethe-Universität Frankfurt am Main · Institute of Theoretical Physics

About

66
Publications
4,335
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1,395
Citations
Citations since 2017
58 Research Items
1357 Citations
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20172018201920202021202220230100200300400500600
20172018201920202021202220230100200300400500600
20172018201920202021202220230100200300400500600
Introduction
Skills and Expertise

Publications

Publications (66)
Article
Full-text available
We report measurements of the gravitationally lensed secondary image—the first in an infinite series of so-called “photon rings”—around the supermassive black hole M87* via simultaneous modeling and imaging of the 2017 Event Horizon Telescope (EHT) observations. The inferred ring size remains constant across the seven days of the 2017 EHT observing...
Article
Full-text available
One of the fundamental conclusions of the Cosmic Battery (a means for producing poloidal magnetic flux in the vicinity of a black hole via the Poynting-Robertson effect on the accretion disk) is that it determines the direction of the axial magnetic field: near the black hole it is parallel to the angular velocity Ω of the surrounding disk, while f...
Preprint
Full-text available
Observations of $\rm SgrA^*$ have provided a lot of insight on low-luminosity accretion, with a handful of bright flares accompanied with orbital motion close to the horizon. It has been proposed that gas supply comes from stellar winds in the neighborhood of the supermassive black hole. We here argue that the flow at the vicinity of the black hole...
Article
Observations of SgrA★ have provided a lot of insight on low-luminosity accretion, with a handful of bright flares accompanied with orbital motion close to the horizon. It has been proposed that gas supply comes from stellar winds in the neighborhood of the supermassive black hole. We here argue that the flow at the vicinity of the black hole has a...
Article
Full-text available
We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for...
Article
Magnetic reconnection is thought to be one of the main energy-dissipation mechanisms fueling energy to the plasma in the vicinity of a black hole. Indeed, plasmoids formed through magnetic reconnection may play a key role in γ-ray, X-ray and near-infrared flares from the black hole at the center of our galaxy, SgrA*. We report the results of three-...
Article
Context. The recent 230 GHz observations of the Event Horizon Telescope are able to image the innermost structure of M 87 and show a ring-like structure that agrees with thermal synchrotron emission generated in a torus surrounding a supermassive black hole. However, at lower frequencies, M 87 is characterised by a large-scale and edge-brightened j...
Article
Full-text available
M87 has been the target of numerous astronomical observations across the electromagnetic spectrum, and very long baseline interferometry has resolved an edge-brightened jet1–4. However, the origin and formation of its jets remain unclear. In our current understanding, black holes (BH) are the driving engine of jet formation5, and indeed the recent...
Article
Full-text available
Multi-messenger astrophysics is becoming a major avenue to explore the Universe, with the potential to span a vast range of redshifts. The growing synergies between different probes is opening new frontiers, which promise profound insights into several aspects of fundamental physics and cosmology. In this context, THESEUS will play a central role d...
Preprint
Full-text available
Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimeter wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to $10-100$ gravitational radii ($r_g=GM/c^2$) scales in nearby sources. Centaurus A is the closest radio-loud source to Earth. It bridges t...
Preprint
Full-text available
Magnetic reconnection is thought to be one of the main energy-dissipation mechanisms fueling energy to the plasma in the vicinity of a black hole. Indeed, plasmoids formed though magnetic reconnection may play a key role in $\gamma$-ray, X-ray and near-infrared flares from the black hole at the center of our galaxy, SgrA*. We report the results of...
Preprint
Full-text available
M87 has been the target of numerous astronomical observations across the electromagnetic spectrum and Very Long Baseline Interferometry (VLBI) resolved an edge-brightened jet. However, the origin and formation of its jets remain unclear. In our current understand black holes (BH) are the driving engine of jet formation, and indeed the recent Event...
Preprint
Full-text available
The recent 230 GHz observations of the Event Horizon Telescope (EHT) are able to image the innermost structure of the M87 and show a ring-like structure which is in agreement with thermal synchrotron emission generated in a torus surrounding a supermassive black hole. However, at lower frequencies M87 is characterised by a large-scale and edge-brig...
Preprint
Full-text available
The black-hole images obtained with the Event Horizon Telescope (EHT) are expected to be variable at the dynamical timescale near their horizons. For the black hole at the center of the M87 galaxy, this timescale (5-61 days) is comparable to the 6-day extent of the 2017 EHT observations. Closure phases along baseline triangles are robust interferom...
Article
Full-text available
Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10–100 gravitational radii ( r g ≡ G M / c ² ) scales in nearby sources ¹ . Centaurus A is the closest radio-loud source to Earth ² . It...
Article
Full-text available
Our understanding of strong gravity near supermassive compact objects has recently improved thanks to the measurements made by the Event Horizon Telescope (EHT). We use here the M87* shadow size to infer constraints on the physical charges of a large variety of nonrotating or rotating black holes. For example, we show that the quality of the measur...
Preprint
Full-text available
Our understanding of strong gravity near supermassive compact objects has recently improved thanks to the measurements made by the Event Horizon Telescope (EHT). We use here the M87* shadow size to infer constraints on the physical charges of a large variety of nonrotating or rotating black holes. For example, we show that the quality of the measur...
Preprint
Full-text available
We present the results from a full polarization study carried out with ALMA during the first VLBI campaign, which was conducted in Apr 2017 in the $\lambda$3mm and $\lambda$1.3mm bands, in concert with the Global mm-VLBI Array (GMVA) and the Event Horizon Telescope (EHT), respectively. We determine the polarization and Faraday properties of all VLB...
Article
Full-text available
Synchrotron radiation from hot gas near a black hole results in a polarized image. The image polarization is determined by effects including the orientation of the magnetic field in the emitting region, relativistic motion of the gas, strong gravitational lensing by the black hole, and parallel transport in the curved spacetime. We explore these ef...
Preprint
Full-text available
Multi-messenger astrophysics is becoming a major avenue to explore the Universe, with the potential to span a vast range of redshifts. The growing synergies between different probes is opening new frontiers, which promise profound insights into several aspects of fundamental physics and cosmology. In this context, THESEUS will play a central role d...
Article
Full-text available
In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ~6.5 × 10⁹ M_⊙. The EHTC also partnered with several international facilit...
Article
Full-text available
Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole. Here we compare the resolved polarization structure observed by the EH...
Article
Full-text available
In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supermassive black hole at the core of the M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. This structure originates from synchrotron emission produced by relativistic plasma located in the immedia...
Article
Full-text available
We present the results from a full polarization study carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) during the first Very Long Baseline Interferometry (VLBI) campaign, which was conducted in 2017 April in the λ3 mm and λ1.3 mm bands, in concert with the Global mm-VLBI Array (GMVA) and the Event Horizon Telescope (EHT), re...
Article
Full-text available
In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supermassive black hole at the core of the M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. This structure originates from synchrotron emission produced by relativistic plasma located in the immedia...
Article
Full-text available
Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole. Here we compare the resolved polarization structure observed by the EH...
Article
Full-text available
We present the results from a full polarization study carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) during the first Very Long Baseline Interferometry (VLBI) campaign, which was conducted in 2017 April in the λ3 mm and λ1.3 mm bands, in concert with the Global mm-VLBI Array (GMVA) and the Event Horizon Telescope (EHT), re...
Article
The detection of the binary events GW170817 and GW190814 has provided invaluable constraints on the maximum mass of nonrotating configurations of neutron stars, M TOV. However, the large differences in the neutron-star masses measured in GW170817 and GW190814 has also lead to significant tension between the predictions for such maximum masses, with...
Article
We perform three-dimensional (3D) general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D simulation confirms our previous results from 2D simulations, namely, that a relativistic magnetized outflow...
Preprint
Full-text available
The detection of the binary events GW170817 and GW190814 has provided invaluable constraints on the maximum mass of nonrotating configurations of neutron stars, $M_{_{\rm TOV}}$. However, the large differences in the neutron-star masses measured in GW170817 and GW190814 has also lead to a significant tension between the predictions for such maximum...
Preprint
We perform three-dimensional (3D) general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D simulation confirms our previous results from 2D simulations, namely, that a relativistic magnetized outflow...
Article
Full-text available
The Event Horizon Telescope (EHT) has recently delivered the first resolved images of M87*, the supermassive black hole in the center of the M87 galaxy. These images were produced using 230 GHz observations performed in 2017 April. Additional observations are required to investigate the persistence of the primary image feature—a ring with azimuthal...
Article
The observations of GW170817/GRB170817A have confirmed that the coalescence of a neutron-star binary is the progenitor of a short gamma-ray burst (GRB). In the standard picture of a short GRB, a collimated highly relativistic outflow is launched after merger and it successfully breaks out from the surrounding ejected matter. Using initial condition...
Article
One of the main dissipation processes acting on all scales in relativistic jets is thought to be governed by magnetic reconnection. Such dissipation processes have been studied in idealized environments, such as reconnection layers, which evolve in merging islands and lead to the production of ‘plasmoids’, ultimately resulting in efficient particle...
Preprint
The observations of GW170817/GRB170817A have confirmed that the coalescence of a neutron-star binary is the progenitor of a short gamma-ray burst. In the standard picture of a short gamma-ray burst, a collimated highly relativistic outflow is launched after merger and it successfully breaks out from the surrounding ejected matter. Using initial con...
Preprint
One of the main dissipation processes acting on all scales in relativistic jets is thought to be governed by magnetic reconnection. Such dissipation processes have been studied in idealized environments, such as reconnection layers, which evolve in merging islands and lead to the production of plasmoids, ultimately resulting in efficient particle a...
Preprint
We present a systematic study of magnetised neutron star head on collisions. We investigate the resulting magnetic field geometries as the two neutron stars merge. Furthermore, we analyze the luminosity produced in these collisions and monitor the evolution of the magnetic fields from the time of merger until the subsequent production of a black ho...
Preprint
Full-text available
Recent advances in black hole astrophysics, particularly the first visual evidence of a supermassive black hole at the center of the galaxy M87 by the Event Horizon Telescope (EHT), and the detection of an orbiting "hot spot" nearby the event horizon of Sgr A* in the Galactic center by the Gravity Collaboration, require the development of novel num...
Article
Context. High-resolution very long baseline interferometry (VLBI) observations of NGC 1052 show a two sided jet with several regions of enhanced emission and a clear emission gap between the two jets. This gap shrinks with increasing frequency and vanishes around ν ∼ 43 GHz. The observed structures are due to both the macroscopic fluid dynamics int...
Article
The main hard pulse of prompt gamma-ray emission in GRB 170817A had a duration of ~0.5 s, and its onset was delayed with respect to the gravitational-wave chirp signal by . Detailed follow-up of the subsequent broadband kilonova emission revealed a two-component ejecta—a lanthanide-poor ejecta with mass M ej,blue ≈ 0.025 M ⊙ that powered the early...
Preprint
High-resolution Very-Long-Baseline Interferometry observations of NGC 1052 show a two sided jet with several regions of enhanced emission and a clear emission gap between the two jets.This gap shrinks with increasing frequency and vanishes around $\nu\sim43$ GHz. The observed structures are due to both the macroscopic fluid dynamics interacting wit...
Preprint
The main hard pulse of prompt gamma-ray emission in GRB$\,$170817A had a duration of $\sim0.5\,{\rm s}$ and its onset was delayed with respect to the gravitational-wave chirp signal by $t_{\rm del} \approx 1.74\,{\rm s}$. Detailed follow-up of the subsequent broadband kilonova emission revealed a two-component ejecta -- a lanthanide-poor ejecta wit...
Article
Binary neutron-star mergers have long been associated with short-duration gamma-ray bursts (GRBs). This connection was confirmed with the first coincident detection of gravitational waves together with electromagnetic radiation from GW170817. The basic paradigm for short-duration GRBs includes an ultra-relativistic jet, but the low-luminosity promp...
Preprint
Binary neutron star mergers have long been associated with short-duration gamma-ray bursts (GRBs). This connection was confirmed with the first coincident detection of gravitational waves together with electromagnetic radiation from GW170817. The basic paradigm for short-duration GRBs includes an ultra-relativistic jet, but the low-luminosity promp...
Article
Full-text available
In the dawn of the multi-messenger era of gravitational wave astronomy, which was marked by the first ever coincident detection of gravitational waves and electromagnetic radiation, it is important to take a step back and consider our current established knowledge. Numerical simulations of binary neutron star mergers and simulations of short GRB je...
Article
It is known that a binary neutron star (BNS) merger produces a hypermassive neutron star. The lifetime of this compact remnant depends on the total mass and the equation of state. The collapse of this compact remnant to a black hole torus system is expected to give rise to a powerful jet and a short gamma-ray burst. Nevertheless, if the collapse is...
Preprint
Full-text available
In the dawn of the multi-messenger era including gravitational waves, which was marked by the first ever coincident detection of gravitational waves and electromagnetic radiation it is important to lay back and think about established knowledge. Numerical simulations of binary neutron star mergers and simulations of short GRB jets have to combine e...
Article
Full-text available
We examine the range of rest-mass densities, temperatures and magnetic fields involved in simulations of binary neutron-star mergers and identify the conditions under which the ideal-magnetohydrodynamics approximation breaks down and hence the magnetic-field decay should be accounted for. We use recent calculations of the conductivities of warm cor...
Article
Full-text available
One of the most luminous explosions detected, gamma-ray bursts, especially the so-called long-duration bursts, most probably consist of an intrinsic core-collapse to a black hole inside a super massive star. We point out that this collapse alone will give a generic gravitational wave burst. It has been shown that the strength of this burst depends...
Article
Full-text available
It has been suggested that a non-repeating fast radio burst (FRB) represents the final signal of a supramassive rotating neutron star that collapses to a black hole because of its continuous spin down due to electromagnetic emission. In this model, a neutron star with a mass above the critical mass for nonrotating models and supported by rapid rota...
Article
Full-text available
It is known that a binary neutron star merger produces a hypermassive neutron star. The lifetime of this compact remnant depends on the total mass and the equation of state. The collapse of this compact remnant to a black- hole-torus system is expected to give rise to a powerful jet and a short gamma-ray burst. Nevertheless, if the collapse is dela...
Article
Full-text available
Primordial black holes are considered to be pair created quantum-mechanically during inflation. In the context of General Relativity (GR), it has been shown that the pair creation rate is exponentially decreasing during inflation. Specifically, tiny black holes are favored in the early universe, but they can grow with the horizon scale, as inflatio...
Article
Full-text available
We implement the KORAL code to perform two sets of very long general relativistic radiation magnetohydrodynamic simulations of an axisymmetric optically thin magnetized flow around a non-rotating black hole: one with a new term in the electromagnetic field tensor due to the radiation pressure felt by the plasma electrons on the comoving frame of th...
Article
Full-text available
In 1977, Blandford and Znajek showed how the spin energy of a rotating black hole may be extracted electromagnetically through a magnetic field that threads the black hole horizon. A characteristic feature of this mechanism is that, under certain fairly general conditions, the energy loss rate decays exponentially. We looked precisely for such beha...
Article
Full-text available
We present the first systematic study of the gravitational collapse of rotating and magnetised neutron stars to charged and rotating (Kerr-Newman) black holes. In particular, we consider the collapse of magnetised and rotating neutron stars assuming that no pair-creation takes place and that the charge density in the magnetosphere is so low that th...
Article
Full-text available
Gamma-ray bursts (GRBs) are violent explosions, coming from cosmological distances. They are detected in gamma-rays (also X-rays, UV, optical, radio) almost every day, and have typical durations of a few seconds to a few minutes. Some GRBs have been reported with extraordinary durations of 104 s, the so-called ultralong GRBs. It has been debated wh...
Article
Gamma-ray bursts (GRBs) are believed to be powered by the electromagnetic extraction of spin energy from a black hole endowed with a magnetic field supported by electric currents in a surrounding disc (Blandford & Znajek). A generic feature of this mechanism is that, under certain fairly general assumptions, the energy loss rate decays exponentiall...
Article
Full-text available
Gamma-ray bursts (GRBs) are violent explosions, coming from cosmological distances. They are detected in gamma-rays (also X-rays, UV, optical, radio) almost every day, and have typical durations of a few seconds to a few minutes. Some GRBs have been reported with extraordinary duration of 10^4 sec. These are called Ultra Long GRBs. It has been deba...
Article
Full-text available
The aberrated radiation pressure at the inner edge of the accretion disk around an astrophysical black hole imparts a relative azimuthal velocity on the electrons with respect to the ions which gives rise to a ring electric current that generates large scale poloidal magnetic field loops. This is the Cosmic Battery established by Contopoulos and Ka...
Article
Full-text available
We investigate a particular subclass of gamma-ray bursts whose prompt X-ray emission lasts for a few hundred seconds and shows a clear exponential decay over more than four orders of magnitude. We associate them with the electromagnetic spindown of the black hole that forms during the core collapse of a supermassive star. Their characteristic spind...
Article
Full-text available
We investigate the structure of the steady-state force-free magnetosphere around a Kerr black hole in various astrophysical settings. The solution Psi(r,theta) depends on the distributions of the magnetic field line angular velocity omega(Psi) and the poloidal electric current I(Psi). These are obtained self-consistently as eigenfunctions that allo...
Article
Full-text available
We explore the analogy between a rotating magnetized black hole and an axisymmetric pulsar and derive its electromagnetic spindown after its formation in the core collapse of a supermassive star. The spindown shows two characteristic phases, an early Blandford-Znajek phase that lasts a few hundred seconds, and a late Kerr-Newman afterglow phase tha...

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