Razieh Emami
A5037694738- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Pulsars and Gravitational Waves Research
- Cosmology and Gravitation Theories
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Gamma-ray bursts and supernovae
- Dark Matter and Cosmic Phenomena
- Geophysics and Gravity Measurements
- Astrophysics and Star Formation Studies
- Black Holes and Theoretical Physics
- Astronomical Observations and Instrumentation
- Radio Astronomy Observations and Technology
- Particle Accelerators and Free-Electron Lasers
- Scientific Research and Discoveries
- Solar and Space Plasma Dynamics
- High-pressure geophysics and materials
- Mechanics and Biomechanics Studies
- Laser-Plasma Interactions and Diagnostics
- Relativity and Gravitational Theory
- Superconducting Materials and Applications
- History and Developments in Astronomy
- High-Energy Particle Collisions Research
- Adaptive optics and wavefront sensing
Center for Astrophysics Harvard & Smithsonian
2019-2024
Harvard University Press
2019-2024
Hong Kong University of Science and Technology
2016-2020
University of Hong Kong
2016-2020
Johns Hopkins University
2015-2016
Nano and Advanced Materials Institute
2015-2016
Institute for Research in Fundamental Sciences
2011-2015
The Abdus Salam International Centre for Theoretical Physics (ICTP)
2013-2014
Shahid Beheshti University
2010
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\%...
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 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...
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...
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 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 use deep JWST/NIRSpec R ∼ 1000 slit spectra of 113 galaxies at $1.7 < z 3.5$, selected from the mass-complete Blue Jay survey, to investigate prevalence and typical properties neutral gas outflows cosmic noon. detect excess Na id absorption (beyond stellar contribution) in 46 per cent massive (log M*/M⊙ > 10), with similar incidence rates star-forming quenching systems. Half profiles are blueshifted by least 100 km s−1, providing unambiguous evidence for outflows....
Abstract Large-scale outflows driven by supermassive black holes are thought to have a fundamental role in suppressing star formation massive galaxies. However, direct observational evidence for this hypothesis is still lacking, particularly the young universe where star-formation quenching remarkably rapid 1–3 , thus requiring effective removal of gas 4 as opposed slow heating 5,6 . Although ionized frequently detected distant galaxies 7 amount ejected mass too small be able suppress 8,9...
Abstract Black hole X-ray binaries exhibit different spectral and timing properties in accretion states. The outburst of a recently discovered extraordinarily bright source, Swift J1727.8–1613, has enabled the first investigation how polarization source evolve with state. 2–8 keV degree was previously measured by Imaging Polarimetry Explorer (IXPE) to be ≈4% hard intermediate Here we present new IXPE results taken soft state, flux dominated thermal disk emission. We find that dropped...
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...
The next-generation Event Horizon Telescope (ngEHT) will be a significant enhancement of the (EHT) array, with ∼10 new antennas and instrumental upgrades existing antennas. increased uv-coverage, sensitivity, frequency coverage allow wide range science opportunities to explored. ngEHT Analysis Challenges have been launched inform development array design, objectives, analysis pathways. For each challenge, synthetic EHT datasets are generated from theoretical source models released challenge...
Abstract The existence of massive quiescent galaxies at high redshift seems to require rapid quenching, but it is unclear whether all have gone through this phase and what physical mechanisms are involved. To study we use rest-frame colors select 12 young z ∼ 1.5. From spectral energy distribution fitting, find that they experienced intense starbursts prior quenching. We confirm with deep Magellan/FIRE spectroscopic observations for a subset seven galaxies. Broad emission lines detected two...
3C84 is a nearby radio source with complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates use VLBI above hitherto available maximum frequency 86GHz. Using ultrahigh resolution observations at highest 228GHz, we aim to directly detect compact structures understand physical conditions in 3C84. We used EHT 228GHz and, given limited (u,v)-coverage, applied geometric model fitting data. also employed...
We present the consistent δN formalism for curvature perturbations in anisotropic cosmological backgrounds. employ our to calculate power spectrum, bispectrum and trispectrum models of inflation with background gauge fields Bianchi I universe. Our results coincide exactly recent obtained from in-in formalism. To satisfy observational constraints anisotropies generated on spectrum are kept small but large orientation-dependent non-Gaussianities can be generated. study Suyama-Yamaguchi...
The blazar J1924-2914 is a primary Event Horizon Telescope (EHT) calibrator for the Galactic Center's black hole Sagittarius A*. Here we present first total and linearly polarized intensity images of this source obtained with unprecedented 20 $\mu$as resolution EHT. very compact flat-spectrum radio strong optical variability polarization. In April 2017 was observed quasi-simultaneously EHT (April 5-11), Global Millimeter VLBI Array 3), Very Long Baseline 28), giving novel view at four...
Abstract We present a framework for characterizing the spatiotemporal power spectrum of variability expected from horizon-scale emission structure around supermassive black holes, and we apply this to library general relativistic magnetohydrodynamic (GRMHD) simulations associated ray-traced images relevant Event Horizon Telescope (EHT) observations Sgr A*. find that is generically red-noise process in both temporal spatial dimensions, with peak occurring on longest timescales largest scales....
Abstract The extraordinary physical resolution afforded by the Event Horizon Telescope has opened a window onto astrophysical phenomena unfolding on horizon scales in two known black holes, M87 * and Sgr A*. However, with this leap come new set of practical complications. A* exhibits intraday variability that violates assumptions underlying Earth aperture synthesis, limiting traditional image reconstruction methods to short timescales data sets very sparse ( u , v ) coverage. We present...
Abstract The driving of turbulence in galaxies is deeply connected with the physics feedback, star formation, outflows, accretion, and radial transport disks. velocity dispersion gas therefore offers a promising observational window into these processes. However, relative importance each mechanisms remains controversial. In this work we revisit possibility that on galactic scales driven by direct impact accreting gaseous material disk. We measure effect disk-like star-forming galaxy...
We report on the observations of quasar NRAO 530 with Event Horizon Telescope (EHT) 2017 April 5-7, when was used as a calibrator for EHT Sagittarius A*. At z=0.902 this is most distant object imaged by so far. reconstruct first images source at 230 GHz, an unprecedented angular resolution $\sim$ 20 $\mu$as, both in total intensity and linear polarization. do not detect variability, allowing us to represent whole data set static images. The reveal bright feature located southern end jet,...