35 research outputs found
Event Horizon Telescope observations of the jet launching and collimation in Centaurus A
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 10â100 gravitational radii (rg ⥠GM/c2) scales in nearby sources. Centaurus A is the closest radio-loud source to Earth2. It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of â43° has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations, we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find that the source structure of Centaurus A resembles the jet in Messier 87 on ~500 rg scales remarkably well. Furthermore, we identify the location of Centaurus Aâs SMBH with respect to its resolved jet core at a wavelength of 1.3 mm and conclude that the sourceâs event horizon shadow should be visible at terahertz frequencies. This location further supports the universal scale invariance of black holes over a wide range of masses.A.C. is an Einstein Fellow of the NASA Hubble Fellowship Program. J.P is an EACOA
fellow. Z.Y. is a UKRI Stephen Hawking Fellow. We thank the following organizations
and programmes: the Academy of Finland (projects 274477, 284495, 312496, 315721);
the Agencia Nacional de InvestigaciĂłn y Desarrollo (ANID), Chile via NCN19_058
(TITANs) and Fondecyt 3190878; the Alexander von Humboldt Stiftung; an Alfred P.
Sloan Research Fellowship; Allegro, the European ALMA Regional Centre node in the
Netherlands, the NL astronomy research network NOVA and the astronomy institutes
of the University of Amsterdam, Leiden University and Radboud University; the Black
Hole Initiative at Harvard University, through a grant (60477) from the John Templeton
Foundation; the China Scholarship Council; Consejo Nacional de Ciencia y TecnologĂa
(CONACYT, Mexico, projects U0004-246083, U0004-259839, F0003-272050, M0037-
279006, F0003-281692, 104497, 275201, 263356, 57265507); the Delaney Family via the Delaney Family John A. Wheeler Chair at Perimeter Institute; DirecciĂłn General
de Asuntos del Personal Académico-Universidad Nacional Autónoma de México
(DGAPA-UNAM, projects IN112417 and IN112820); the EACOA Fellowship of the
East Asia Core Observatories Association; the European Research Council Synergy
Grant âBlackHoleCam: Imaging the Event Horizon of Black Holesâ (grant 610058);
the Generalitat Valenciana postdoctoral grant APOSTD/2018/177 and GenT Program
(project CIDEGENT/2018/021); MICINN Research Project PID2019-108995GB-C22;
the Gordon and Betty Moore Foundation (grants GBMF- 3561, GBMF-5278); the
Istituto Nazionale di Fisica Nucleare (INFN) sezione di Napoli, iniziative specifiche
TEONGRAV; the International Max Planck Research School for Astronomy and
Astrophysics at the Universities of Bonn and Cologne; Joint Princeton/Flatiron and
Joint Columbia/Flatiron Postdoctoral Fellowships, research at the Flatiron Institute is
supported by the Simons Foundation; the Japanese Government (Monbukagakusho:
MEXT) Scholarship; the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid
for JSPS Research Fellowship (JP17J08829); the Key Research Program of Frontier
Sciences, Chinese Academy of Sciences (CAS, grants QYZDJ-SSW-SLH057, QYZDJSSWSYS008,
ZDBS-LY-SLH011).
We further thank the Leverhulme Trust Early Career Research Fellowship; the
Max-Planck-Gesellschaft (MPG); the Max Planck Partner Group of the MPG and
the CAS; the MEXT/JSPS KAKENHI (grants 18KK0090, JP18K13594, JP18K03656,
JP18H03721, 18K03709, 18H01245, JP19H01943, 25120007); the Malaysian
Fundamental Research Grant Scheme (FRGS) FRGS/1/2019/STG02/UM/02/6; the
MIT International Science and Technology Initiatives (MISTI) Funds; the Ministry
of Science and Technology (MOST) of Taiwan (105- 2112-M-001-025-MY3, 106-
2112-M-001-011, 106-2119- M-001-027, 107-2119-M-001-017, 107-2119-M-001- 020, 107-2119-M-110-005, 108-2112-M-001-048, and 109-2124-M-001-005); the
National Aeronautics and Space Administration (NASA, Fermi Guest Investigator
grant 80NSSC20K1567, NASA Astrophysics Theory Program grant 80NSSC20K0527,
NASA grant NNX17AL82G, and Hubble Fellowship grant HST-HF2-51431.001-A
awarded by the Space Telescope Science Institute, which is operated by the Association
of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-
26555, and NASA NuSTAR award 80NSSC20K0645); the National Institute of Natural
Sciences (NINS) of Japan; the National Key Research and Development Program of
China (grant 2016YFA0400704, 2016YFA0400702); the National Science Foundation
(NSF, grants AST-0096454, AST-0352953, AST-0521233, AST-0705062, AST-0905844,
AST-0922984, AST-1126433, AST-1140030, DGE-1144085, AST-1207704, AST-
1207730, AST-1207752, MRI-1228509, OPP-1248097, AST-1310896, AST-1337663,
AST-1440254, AST-1555365, AST-1615796, AST-1715061, AST-1716327, AST-
1716536, OISE-1743747, AST-1816420, AST-1903847, AST-1935980, AST-2034306);
the Natural Science Foundation of China (grants 11573051, 11633006, 11650110427,
10625314, 11721303, 11725312, 11933007, 11991052, 11991053); a fellowship of
China Postdoctoral Science Foundation (2020M671266); the Natural Sciences and
Engineering Research Council of Canada (NSERC, including a Discovery Grant and
the NSERC Alexander Graham Bell Canada Graduate Scholarships-Doctoral Program);
the National Research Foundation of Korea (the Global PhD Fellowship Grant: grants
2014H1A2A1018695, NRF-2015H1A2A1033752, 2015- R1D1A1A01056807, the Korea
Research Fellowship Program: NRF-2015H1D3A1066561, Basic Research Support Grant
2019R1F1A1059721); the Netherlands Organization for Scientific Research (NWO)
VICI award (grant 639.043.513) and Spinoza Prize SPI 78-409; the New Scientific
Frontiers with Precision Radio Interferometry Fellowship awarded by the South African
Radio Astronomy Observatory (SARAO), which is a facility of the National Research
Foundation (NRF), an agency of the Department of Science and Innovation (DSI) of
South Africa; the South African Research Chairs Initiative of the Department of Science
and Innovation and National Research Foundation; the Onsala Space Observatory
(OSO) national infrastructure, for the provisioning of its facilities/observational support (OSO receives funding through the Swedish Research Council under grant 2017-
00648) the Perimeter Institute for Theoretical Physics (research at Perimeter Institute
is supported by the Government of Canada through the Department of Innovation,
Science and Economic Development and by the Province of Ontario through the
Ministry of Research, Innovation and Science); the Spanish Ministerio de EconomĂa
y Competitividad (grants PGC2018-098915-B-C21, AYA2016-80889-P, PID2019-
108995GB-C21); the State Agency for Research of the Spanish MCIU through the âCenter
of Excellence Severo Ochoaâ award for the Instituto de AstrofĂsica de AndalucĂa (SEV-
2017- 0709); the Toray Science Foundation; the ConsejerĂa de EconomĂa, Conocimiento,
Empresas y Universidad of the Junta de AndalucĂa (grant P18-FR-1769), the Consejo
Superior de Investigaciones CientĂficas (grant 2019AEP112); the US Department of
Energy (US DOE) through the Los Alamos National Laboratory (operated by Triad
National Security, LLC, for the National Nuclear Security Administration of the US
DOE (Contract 89233218CNA000001); the European Unionâs Horizon 2020 research
and innovation programme under grant agreement No 730562 RadioNet; ALMA North
America Development Fund; the Academia Sinica; Chandra TM6- 17006X and DD7-
18089X; the GenT Program (Generalitat Valenciana) Project CIDEGENT/2018/021.
This work used the Extreme Science and Engineering Discovery Environment
(XSEDE), supported by NSF grant ACI-1548562, and CyVerse, supported by NSF grants
DBI-0735191, DBI-1265383, and DBI-1743442. XSEDE Stampede2 resource at TACC
was allocated through TG-AST170024 and TG-AST080026N. XSEDE JetStream resource
at PTI and TACC was allocated through AST170028. The simulations were performed
in part on the SuperMUC cluster at the LRZ in Garching, on the LOEWE cluster in
CSC in Frankfurt, and on the HazelHen cluster at the HLRS in Stuttgart. This research was enabled in part by support provided by Compute Ontario (http://computeontario.
ca), Calcul Quebec (http://www.calculquebec.ca) and Compute Canada (http://www.
computecanada.ca). We thank the staff at the participating observatories, correlation
centres, and institutions for their enthusiastic support.
This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.01198.V.
ALMA is a partnership of the European Southern Observatory (ESO; Europe,
representing its member states), NSF, and National Institutes of Natural Sciences of Japan,
together with National Research Council (Canada), Ministry of Science and Technology
(MOST; Taiwan), Academia Sinica Institute of Astronomy and Astrophysics (ASIAA;
Taiwan), and Korea Astronomy and Space Science Institute (KASI; Republic of Korea), in
cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO,
Associated Universities, Inc. (AUI)/NRAO, and the National Astronomical Observatory of
Japan (NAOJ). The NRAO is a facility of the NSF operated under cooperative agreement
by AUI. APEX is a collaboration between the Max-Planck-Institut fĂŒr Radioastronomie
(Germany), ESO, and the Onsala Space Observatory (Sweden). The SMA is a joint project
between the SAO and ASIAA and is funded by the Smithsonian Institution and the
Academia Sinica. The JCMT is operated by the East Asian Observatory on behalf of the
NAOJ, ASIAA, and KASI, as well as the Ministry of Finance of China, Chinese Academy
of Sciences, and the National Key R&D Program (No. 2017YFA0402700) of China.
Additional funding support for the JCMT is provided by the Science and Technologies
Facility Council (UK) and participating universities in the UK and Canada. The LMT is a
project operated by the Instituto Nacional de AstrĂłfisica, Ăptica, y ElectrĂłnica (Mexico)
and the University of Massachusetts at Amherst (USA), with financial support from
the Consejo Nacional de Ciencia y TecnologĂa and the National Science Foundation.
The IRAM 30-m telescope on Pico Veleta, Spain is operated by IRAM and supported
by CNRS (Centre National de la Recherche Scientifique, France), MPG (Max-Planck-
Gesellschaft, Germany) and IGN (Instituto GeogrĂĄfico Nacional, Spain). The SMT is
operated by the Arizona Radio Observatory, a part of the Steward Observatory of the
University of Arizona, with financial support of operations from the State of Arizona and
financial support for instrumentation development from the NSF. The SPT is supported
by the National Science Foundation through grant PLR- 1248097. Partial support is also
provided by the NSF Physics Frontier Center grant PHY-1125897 to the Kavli Institute of
Cosmological Physics at the University of Chicago, the Kavli Foundation and the Gordon
and Betty Moore Foundation grant GBMF 947. The SPT hydrogen maser was provided
on loan from the GLT, courtesy of ASIAA. The EHTC has received generous donations
of FPGA chips from Xilinx Inc., under the Xilinx University Program. The EHTC has benefited from technology shared under open-source license by the Collaboration for
Astronomy Signal Processing and Electronics Research (CASPER). The EHT project is
grateful to T4Science and Microsemi for their assistance with Hydrogen Masers. This
research has made use of NASAâs Astrophysics Data System. We gratefully acknowledge
the support provided by the extended staff of the ALMA, both from the inception of the
ALMA Phasing Project through the observational campaigns of 2017 and 2018. We would
like to thank A. Deller and W. Brisken for EHT-specific support with the use of DiFX. We
acknowledge the significance that Maunakea, where the SMA and JCMT EHT stations are
located, has for the indigenous Hawaiian people.
The grants listed above collectively fund the Event Horizon Telescope project.http://www.nature.com/natureastronomyam2023Physic
First Sagittarius A* Event Horizon Telescope Results. VII. Polarization of the Ring
The Event Horizon Telescope observed the horizon-scale synchrotron emission region around the Galactic center supermassive black hole, Sagittarius A* (Sgr A*), in 2017. These observations revealed a bright, thick ring morphology with a diameter of 51.8 ± 2.3 ÎŒas and modest azimuthal brightness asymmetry, consistent with the expected appearance of a black hole with mass M â 4 Ă 106 M â. From these observations, we present the first resolved linear and circular polarimetric images of Sgr A*. The linear polarization images demonstrate that the emission ring is highly polarized, exhibiting a prominent spiral electric vector polarization angle pattern with a peak fractional polarization of âŒ40% in the western portion of the ring. The circular polarization images feature a modestly (âŒ5%â10%) polarized dipole structure along the emission ring, with negative circular polarization in the western region and positive circular polarization in the eastern region, although our methods exhibit stronger disagreement than for linear polarization. We analyze the data using multiple independent imaging and modeling methods, each of which is validated using a standardized suite of synthetic data sets. While the detailed spatial distribution of the linear polarization along the ring remains uncertain owing to the intrinsic variability of the source, the spiraling polarization structure is robust to methodological choices. The degree and orientation of the linear polarization provide stringent constraints for the black hole and its surrounding magnetic fields, which we discuss in an accompanying publication
The Polarized Image of a Synchrotron-emitting Ring of Gas Orbiting a Black Hole
Abstract: 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 effects using a simple model of an axisymmetric, equatorial accretion disk around a Schwarzschild black hole. By using an approximate expression for the null geodesics derived by Beloborodov and conservation of the WalkerâPenrose constant, we provide analytic estimates for the image polarization. We test this model using currently favored general relativistic magnetohydrodynamic simulations of M87*, using ring parameters given by the simulations. For a subset of these with modest Faraday effects, we show that the ring model broadly reproduces the polarimetric image morphology. Our model also predicts the polarization evolution for compact flaring regions, such as those observed from Sgr A* with GRAVITY. With suitably chosen parameters, our simple model can reproduce the EVPA pattern and relative polarized intensity in Event Horizon Telescope images of M87*. Under the physically motivated assumption that the magnetic field trails the fluid velocity, this comparison is consistent with the clockwise rotation inferred from total intensity images
Selective Dynamical Imaging of Interferometric Data
Recent developments in very long baseline interferometry (VLBI) have made it possible for the Event Horizon Telescope (EHT) to resolve the innermost accretion flows of the largest supermassive black holes on the sky. The sparse nature of the EHT's (u, v)-coverage presents a challenge when attempting to resolve highly time-variable sources. We demonstrate that the changing (u, v)-coverage of the EHT can contain regions of time over the course of a single observation that facilitate dynamical imaging. These optimal time regions typically have projected baseline distributions that are approximately angularly isotropic and radially homogeneous. We derive a metric of coverage quality based on baseline isotropy and density that is capable of ranking array configurations by their ability to produce accurate dynamical reconstructions. We compare this metric to existing metrics in the literature and investigate their utility by performing dynamical reconstructions on synthetic data from simulated EHT observations of sources with simple orbital variability. We then use these results to make recommendations for imaging the 2017 EHT Sgr A* data set
First M87 Event Horizon Telescope Results. VII. Polarization of the Ring
Abstract: 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 immediate vicinity of the black hole. Here we present the corresponding linear-polarimetric EHT images of the center of M87. We find that only a part of the ring is significantly polarized. The resolved fractional linear polarization has a maximum located in the southwest part of the ring, where it rises to the level of âŒ15%. The polarization position angles are arranged in a nearly azimuthal pattern. We perform quantitative measurements of relevant polarimetric properties of the compact emission and find evidence for the temporal evolution of the polarized source structure over one week of EHT observations. The details of the polarimetric data reduction and calibration methodology are provided. We carry out the data analysis using multiple independent imaging and modeling techniques, each of which is validated against a suite of synthetic data sets. The gross polarimetric structure and its apparent evolution with time are insensitive to the method used to reconstruct the image. These polarimetric images carry information about the structure of the magnetic fields responsible for the synchrotron emission. Their physical interpretation is discussed in an accompanying publication
The polarized image of a synchrotron-emitting ring of gas orbiting a black hole
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 effects using a simple model of an axisymmetric, equatorial accretion disk around a Schwarzschild black
hole. By using an approximate expression for the null geodesics derived by Beloborodov and conservation of the
WalkerâPenrose constant, we provide analytic estimates for the image polarization. We test this model using
currently favored general relativistic magnetohydrodynamic simulations of M87*, using ring parameters given by
the simulations. For a subset of these with modest Faraday effects, we show that the ring model broadly reproduces
the polarimetric image morphology. Our model also predicts the polarization evolution for compact flaring regions,
such as those observed from Sgr A* with GRAVITY. With suitably chosen parameters, our simple model can
reproduce the EVPA pattern and relative polarized intensity in Event Horizon Telescope images of M87*. Under
the physically motivated assumption that the magnetic field trails the fluid velocity, this comparison is consistent
with the clockwise rotation inferred from total intensity images.http://iopscience.iop.org/0004-637Xam2023Physic
First M87 Event Horizon Telescope Results. IX. Detection of Near-horizon Circular Polarization
Event Horizon Telescope (EHT) observations have revealed a bright ring of emission around the supermassive black hole at the center of the M87 galaxy. EHT images in linear polarization have further identified a coherent spiral pattern around the black hole, produced from ordered magnetic fields threading the emitting plasma. Here we present the first analysis of circular polarization using EHT data, acquired in 2017, which can potentially provide additional insights into the magnetic fields and plasma composition near the black hole. Interferometric closure quantities provide convincing evidence for the presence of circularly polarized emission on event-horizon scales. We produce images of the circular polarization using both traditional and newly developed methods. All methods find a moderate level of resolved circular polarization across the image (ăâŁvâŁă < 3.7%), consistent with the low image-integrated circular polarization fraction measured by the Atacama Large Millimeter/submillimeter Array (âŁv int⣠< 1%). Despite this broad agreement, the methods show substantial variation in the morphology of the circularly polarized emission, indicating that our conclusions are strongly dependent on the imaging assumptions because of the limited baseline coverage, uncertain telescope gain calibration, and weakly polarized signal. We include this upper limit in an updated comparison to general relativistic magnetohydrodynamic simulation models. This analysis reinforces the previously reported preference for magnetically arrested accretion flow models. We find that most simulations naturally produce a low level of circular polarization consistent with our upper limit and that Faraday conversion is likely the dominant production mechanism for circular polarization at 230 GHz in M87*
First Sagittarius A* Event Horizon Telescope Results. VIII. Physical Interpretation of the Polarized Ring
In a companion paper, we present the first spatially resolved polarized image of Sagittarius A* on event horizon scales, captured using the Event Horizon Telescope, a global very long baseline interferometric array operating at a wavelength of 1.3 mm. Here we interpret this image using both simple analytic models and numerical general relativistic magnetohydrodynamic (GRMHD) simulations. The large spatially resolved linear polarization fraction (24%â28%, peaking at âŒ40%) is the most stringent constraint on parameter space, disfavoring models that are too Faraday depolarized. Similar to our studies of M87*, polarimetric constraints reinforce a preference for GRMHD models with dynamically important magnetic fields. Although the spiral morphology of the polarization pattern is known to constrain the spin and inclination angle, the time-variable rotation measure (RM) of Sgr A* (equivalent to â46° ± 12° rotation at 228 GHz) limits its present utility as a constraint. If we attribute the RM to internal Faraday rotation, then the motion of accreting material is inferred to be counterclockwise, contrary to inferences based on historical polarized flares, and no model satisfies all polarimetric and total intensity constraints. On the other hand, if we attribute the mean RM to an external Faraday screen, then the motion of accreting material is inferred to be clockwise, and one model passes all applied total intensity and polarimetric constraints: a model with strong magnetic fields, a spin parameter of 0.94, and an inclination of 150°. We discuss how future 345 GHz and dynamical imaging will mitigate our present uncertainties and provide additional constraints on the black hole and its accretion flow
Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
Abstract: 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 âŒ6.5 Ă 109 M â. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87âs spectrum. We can exclude that the simultaneous Îł-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the Îł-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded