Jason Dexter
A5054761800- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Astrophysics and Cosmic Phenomena
- Stellar, planetary, and galactic studies
- Galaxies: Formation, Evolution, Phenomena
- Gamma-ray bursts and supernovae
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Adaptive optics and wavefront sensing
- Radio Astronomy Observations and Technology
- Astronomical Observations and Instrumentation
- Mechanics and Biomechanics Studies
- High-pressure geophysics and materials
- Geophysics and Gravity Measurements
- Astro and Planetary Science
- Heat Transfer Mechanisms
- Solar and Space Plasma Dynamics
- Particle Accelerators and Free-Electron Lasers
- Cosmology and Gravitation Theories
- Relativity and Gravitational Theory
- Particle Detector Development and Performance
- Atmospheric Ozone and Climate
- Laser-Plasma Interactions and Diagnostics
- Atomic and Subatomic Physics Research
- Calibration and Measurement Techniques
University of Colorado System
2019-2025
Max Planck Institute for Extraterrestrial Physics
2015-2024
Joint Institute for Laboratory Astrophysics
2019-2024
University of Colorado Boulder
2019-2024
National Institute of Standards and Technology
2020-2024
Harvard University
2019-2020
Max Planck Innovation
2019
Max Planck Society
2016-2019
University of California, Santa Barbara
2017
University of California, Davis
2016
When surrounded by a transparent emission region, black holes are expected to reveal dark shadow caused gravitational light bending and photon capture at the event horizon. To image study this phenomenon, we have assembled Event Horizon Telescope, global very long baseline interferometry array observing wavelength of 1.3 mm. This allows us reconstruct event-horizon-scale images supermassive hole candidate in center giant elliptical galaxy M87. We resolved central compact radio source as an...
We present measurements of the properties central radio source in M87 using Event Horizon Telescope data obtained during 2017 campaign. develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) two independent sampling algorithms that consider distinct representations visibility data. show family is statistically preferred over other comparably complex we explore. calibrate model parameters general relativistic magnetohydrodynamic (GRMHD) emission...
We present the first Event Horizon Telescope (EHT) images of M87, using observations from April 2017 at 1.3 mm wavelength. These show a prominent ring with diameter ~40 micro-as, consistent size and shape lensed photon orbit encircling "shadow" supermassive black hole. The is persistent across four observing nights shows enhanced brightness in south. To assess reliability these results, we implemented two-stage imaging procedure. In stage, teams, each blind to others' work, produced M87 both...
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\%...
The Event Horizon Telescope (EHT) has mapped the central compact radio source of elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider physical implications asymmetric ring seen in 2017 EHT data. To this end, construct a large library models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by ray tracing. We compare observed visibilities confirm that is consistent earlier predictions strong gravitational...
The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter- and submillimeter-wavelength telescopes separated by distances comparable to the diameter of Earth. At nominal operating wavelength ~1.3 mm, EHT angular resolution (lambda/D) ~25 micro-as, which sufficient resolve nearby supermassive black hole candidates on spatial temporal scales correspond their event horizons. With this capability, scientific goals are probe general...
The highly elliptical, 16-year-period orbit of the star S2 around massive black hole candidate Sgr A ✻ is a sensitive probe gravitational field in Galactic centre. Near pericentre at 120 AU ≈ 1400 Schwarzschild radii, has an orbital speed ≈7650 km s −1 , such that first-order effects Special and General Relativity have now become detectable with current capabilities. Over past 26 years, we monitored radial velocity motion on sky S2, mainly SINFONI NACO adaptive optics instruments ESO Very...
We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3mm radio wavelength observations supermassive black hole candidate at center galaxy M87 quasar 3C 279, taken during 2017 April 5-11 observing campaign. These global very long baseline interferometric include for first time highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA); reaching an angular resolution 25 micro-as, with characteristic sensitivity limits ~1 mJy on baselines to ALMA ~10 other...
GRAVITY is a new instrument to coherently combine the light of European Southern Observatory Very Large Telescope Interferometer form telescope with an equivalent 130 m diameter angular resolution and collecting area 200 m$^2$. The comprises fiber fed integrated optics beam combination, high spectroscopy, built-in analysis control, near-infrared wavefront sensing, phase-tracking, dual operation laser metrology [...]. This article gives overview reports on performance first astronomical...
Using 25 years of data from uninterrupted monitoring stellar orbits in the Galactic Center, we present an update main results this unique set: A measurement mass and distance to SgrA*. Our progress is not only due eight year increase time base, but also improved definition coordinate system. The star S2 continues yield best constraints on SgrA*; statistical errors 0.13 x 10^6 M_sun 0.12 kpc have halved compared previous study. orbit fit robust does need any prior information. system priors,...
The star S2 orbiting the compact radio source Sgr A* is a precision probe of gravitational field around closest massive black hole (candidate). Over last 2.7 decades we have monitored star’s radial velocity and motion on sky, mainly with SINFONI NACO adaptive optics (AO) instruments ESO VLT, since 2017, four-telescope interferometric beam combiner instrument GRAVITY. In this Letter report first detection General Relativity (GR) Schwarzschild Precession (SP) in S2’s orbit. Owing to its highly...
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...
We report the detection of continuous positional and polarization changes compact source SgrA* in high states ('flares') its variable near- infrared emission with near-infrared GRAVITY-Very Large Telescope Interferometer (VLTI) beam-combining instrument. In three prominent bright flares, position centroids exhibit clockwise looped motion on sky, scales typically 150 micro-arcseconds over a few tens minutes, corresponding to about 30% speed light. At same time, flares rotation angle,...
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...
Most supermassive black holes (SMBHs) are accreting at very low levels and difficult to distinguish from the galaxy centers where they reside. Our own Galaxy's SMBH provides a uniquely instructive exception, we present close-up view of its quiescent X-ray emission based on 3 mega-second Chandra observations. Although is elongated aligns well with surrounding disk massive stars, can rule out concentration low-mass coronally active stars as origin lack predicted Fe Kalpha emission. The...
The 2017 Event Horizon Telescope (EHT) observations of the central source in M87 have led to first measurement size a black-hole shadow. This observation offers new and clean gravitational test metric strong-field regime. We show analytically that spacetimes deviate from Kerr but satisfy weak-field tests can lead large deviations predicted shadows are inconsistent with even current EHT measurements. use numerical calculations regular, parametric, non-Kerr metrics identify common...
We present a 0.16% precise and 0.27% accurate determination of R0, the distance to Galactic Center. Our measurement uses star S2 on its 16-year orbit around massive black hole Sgr A* that we followed astrometrically spectroscopically for 27 years. Since 2017, added near-infrared interferometry with VLTI beam combiner GRAVITY, yielding direct separation vector between an accuracy as good 20 micro-arcsec in best cases. passed pericenter highly eccentric May 2018, passage dense sampling...
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...
Magnetic fields near the event horizon Astronomers have long sought to examine a black hole's horizon—the boundary around hole within which nothing can escape. Johnson et al. used sophisticated interferometry techniques combine data from millimeter-wavelength telescopes world. They measured polarization just outside of Sgr A*, supermassive at center our galaxy, Milky Way. The is signature ordered magnetic generated in accretion disk hole. results help explain how holes accrete gas and launch...
The stars orbiting the compact radio source Sgr A* in Galactic Centre are precision probes of gravitational field around closest massive black hole. In addition to adaptive optics assisted astrometry (with NACO / VLT) and spectroscopy SINFONI VLT, NIRC2 Keck GNIRS Gemini) over three decades, since 2016/2017 we have obtained 30-100 mu-as with four-telescope interferometric beam combiner GRAVITY VLTI reaching a sensitivity mK = 20 when combining data from one night. We present simultaneous...