Joseph Farah
A5059915304- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Radio Astronomy Observations and Technology
- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Solar and Space Plasma Dynamics
- Astronomy and Astrophysical Research
- Particle Accelerators and Free-Electron Lasers
- History and Developments in Astronomy
- Ionosphere and magnetosphere dynamics
- Mechanics and Biomechanics Studies
- Galaxies: Formation, Evolution, Phenomena
- Dark Matter and Cosmic Phenomena
- Particle Detector Development and Performance
- Neutrino Physics Research
- Atmospheric Ozone and Climate
- Astronomical Observations and Instrumentation
- Relativity and Gravitational Theory
- Digital Holography and Microscopy
- Diverse multidisciplinary academic research
- Optical measurement and interference techniques
- Nuclear Issues and Defense
- Cosmology and Gravitation Theories
Las Cumbres Observatory Global Telescope Network
2022-2025
University of California, Santa Barbara
2022-2025
Center for Astrophysics Harvard & Smithsonian
2019-2024
University of Massachusetts Boston
2019-2022
Harvard University
2019-2022
Woodwell Climate Research Center
2019-2022
Harvard University Press
2019
We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A$^*$), Galactic center source associated with a supermassive black hole. These were conducted in 2017 using global interferometric array eight telescopes operating at wavelength $\lambda=1.3\,{\rm mm}$. The EHT data resolve compact emission region intrahour variability. A variety imaging and modeling analyses all support an image that is dominated by bright, thick ring diameter $51.8 \pm 2.3$\,\uas (68\%...
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 synchrotron radiation probes structure of magnetic fields and plasma properties near hole. Here we compare resolved polarization observed by EHT, along with simultaneous unresolved Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models. The low fractional linear image suggests that is scrambled scales...
Astrophysical black holes are expected to be described by the Kerr metric. This is only stationary, vacuum, axisymmetric metric, without electromagnetic charge, that satisfies Einstein's equations and does not have pathologies outside of event horizon. We present new constraints on potential deviations from prediction based 2017 EHT observations Sagittarius A* (Sgr A*). calibrate relationship between geometrically defined hole shadow observed size ring-like images using a library includes...
Abstract In this paper we provide a first physical interpretation for the Event Horizon Telescope's (EHT) 2017 observations of Sgr A*. Our main approach is to compare resolved EHT data at 230 GHz and unresolved non-EHT from radio X-ray wavelengths predictions library models based on time-dependent general relativistic magnetohydrodynamics simulations, including aligned, tilted, stellar-wind-fed simulations; radiative transfer performed assuming both thermal nonthermal electron distribution...
Abstract In 2017 April, the Event Horizon Telescope (EHT) observed near-horizon region around supermassive black hole at core of 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 immediate vicinity hole. Here we present corresponding linear-polarimetric EHT images center M87. We find that only part ring is significantly polarized. The...
Abstract We present the first event-horizon-scale images and spatiotemporal analysis of Sgr A* taken with Event Horizon Telescope in 2017 April at a wavelength 1.3 mm. Imaging has been conducted through surveys over wide range imaging assumptions using classical CLEAN algorithm, regularized maximum likelihood methods, Bayesian posterior sampling method. Different prescriptions have used to account for scattering effects by interstellar medium toward Galactic center. Mitigation rapid intraday...
A black hole image contains a series of increasingly narrow rings measurable with progressively longer interferometers.
We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at position supermassive black hole Sagittarius A* (Sgr A*), collected during 2017 April 5--11 campaign. The observations were carried out with eight facilities six locations across globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. majority emission arises from horizon scales, where intrinsic structural variability is detected on timescales minutes hours. effects...
In this paper we quantify the temporal variability and image morphology of horizon-scale emission from Sgr A*, as observed by EHT in 2017 April at a wavelength 1.3 mm. We find that A* data exhibit exceeds what can be explained uncertainties or effects interstellar scattering. The magnitude substantial fraction correlated flux density, reaching $\sim$100\% on some baselines. Through an exploration simple geometric source models, demonstrate ring-like morphologies provide better fits to than...
Our understanding of strong gravity near supermassive compact objects has recently improved thanks to the measurements made by Event Horizon Telescope (EHT). We use here M87* shadow size infer constraints on physical charges a large variety nonrotating or rotating black holes. For example, we show that quality is already sufficient rule out highly charged dilaton hole. Similarly, when considering holes with two and independent charges, are able exclude considerable regions space parameters...
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...
Abstract We present the discovery of Type II supernova SN 2023ixf in M101 and follow-up photometric spectroscopic observations, respectively, first month week its evolution. Our was made within a day estimated light, following light curve is characterized by rapid rise (≈5 days) to luminous peak ( M V ≈ − 18.2 mag) plateau 17.6 extending 30 days with fast decline rate ≈0.03 mag −1 . During rising phase, U color shows blueward evolution, followed redward evolution phase. Prominent flash...
Abstract We present the optical spectroscopic evolution of SN 2023ixf seen in subnight cadence spectra from 1.18 to 15 days after explosion. identify high-ionization emission features, signatures interaction with material surrounding progenitor star, that fade over first 7 days, rapid between observed within same night. compare lines and their relative strength those other supernovae early interaction, finding a close match 2020pni 2017ahn spectrum 2014G at later epochs. To physically...
Abstract We present the densely sampled early light curve of Type II supernova (SN) 2023ixf, first observed within hours explosion in nearby Pinwheel Galaxy (Messier 101; 6.7 Mpc). Comparing these data to recently updated models shock-cooling emission, we find that progenitor likely had a radius 410 ± 10 R ⊙ . Our estimate is model dependent but consistent with red supergiant. These provide good fit starting about 1 day after explosion, despite fact classification spectrum shows signatures...
Abstract Event Horizon Telescope (EHT) observations have revealed a bright ring of emission around the supermassive black hole at center M87 galaxy. EHT images in linear polarization further identified coherent spiral pattern hole, produced from ordered magnetic fields threading emitting plasma. Here we present first analysis circular using data, acquired 2017, which can potentially provide additional insights into and plasma composition near hole. Interferometric closure quantities...
Abstract The Event Horizon Telescope observed the horizon-scale synchrotron emission region around Galactic center supermassive black hole, Sagittarius A* (Sgr A*), in 2017. These observations revealed a bright, thick ring morphology with diameter of 51.8 ± 2.3 μ as and modest azimuthal brightness asymmetry, consistent expected appearance hole mass M ≈ 4 × 10 6 ⊙ . From these observations, we present first resolved linear circular polarimetric images Sgr A*. polarization demonstrate that is...
Abstract In a companion paper, we present the first spatially resolved polarized image of Sagittarius A* on event horizon scales, captured using Event Horizon Telescope, global very long baseline interferometric array operating at wavelength 1.3 mm. Here interpret this both simple analytic models and numerical general relativistic magnetohydrodynamic (GRMHD) simulations. The large linear polarization fraction (24%–28%, peaking ∼40%) is most stringent constraint parameter space, disfavoring...
In April 2019, the Event Horizon Telescope (EHT) Collaboration reported first-ever event-horizon-scale images of a black hole, resolving central compact radio source in giant elliptical galaxy M 87. These reveal ring with southerly brightness distribution and diameter ∼42 μas, consistent predicted size shape shadow produced by gravitationally lensed emission around supermassive hole. results were obtained as part 2017 EHT observation campaign, using global very long baseline interferometric...
Abstract We present ultraviolet/optical/near-infrared observations and modeling of Type II supernovae (SNe II) whose early time ( δ t < 2 days) spectra show transient, narrow emission lines from shock ionization confined r 10 15 cm) circumstellar material (CSM). The observed electron-scattering broadened line profiles (i.e., IIn-like) H i , He i/ii C iv N iii/iv/v the CSM persist on a characteristic timescale IIn ) that marks transition to lower-density emergence Doppler-broadened...
We present the Black Hole Explorer (BHEX), a mission that will produce sharpest images in history of astronomy by extending submillimeter Very-Long-Baseline Interferometry (VLBI) to space. BHEX discover and measure bright narrow "photon ring" is predicted exist black holes, produced from light has orbited hole before escaping. This discovery expose universal features hole's spacetime are distinct complex astrophysics emitting plasma, allowing first direct measurements supermassive spin. In...
Abstract The Event Horizon Telescope (EHT) is a very long-baseline interferometer built to image supermassive black holes on event-horizon scales. In this paper, we investigate candidate sites for an expanded EHT array with improved imaging capabilities. We use historical meteorology and radiative transfer analysis evaluate site performance. Most of the existing in have median zenith opacity less than 0.2 at 230 GHz during March/April observing season. Seven 345 0.5 months. Out more 40 new...
In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing first direct image of center M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole mass approximately 6.5 x 10^9 M_solar. EHTC also partnered several international facilities space on ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents results analysis this campaign, as well...
We report on the polarized light curves of Galactic Center supermassive black hole Sagittarius A * , obtained at millimeter wavelength with Atacama Large Millimeter/submillimeter Array (ALMA). The observations took place as a part Event Horizon Telescope campaign. compare taken during low variability source state 2017 Apr. 6 and 7 those immediately after X-ray flare 11. For latter case, we observe rotation electric vector position angle timescale ∼70 min. interpret this signature equatorial...
Abstract Synchrotron radiation from hot gas near a black hole results in polarized image. The image polarization is determined by effects including the orientation of magnetic field emitting region, relativistic motion gas, strong gravitational lensing hole, and parallel transport curved spacetime. We explore these using simple model an axisymmetric, equatorial accretion disk around Schwarzschild hole. By approximate expression for null geodesics derived Beloborodov conservation...
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...