Towards the event horizon -- the supermassive black hole in the Galactic Center

Abstract

The center of our Galaxy hosts the best constrained supermassive black hole in the universe, Sagittarius A* (Sgr A*). Its mass and distance have been accurately determined from stellar orbits and proper motion studies, respectively, and its high-frequency radio, and highly variable near-infrared and X-ray emission originate from within a few Schwarzschild radii of the event horizon. The theory of general relativity (GR) predicts the appearance of a black hole shadow, which is a lensed image of the event horizon. This shadow can be resolved by very long baseline radio interferometry and test basic predictions of GR and alternatives thereof. In this paper we review our current understanding of the physical properties of Sgr A*, with a particular emphasis on the radio properties, the black hole shadow, and models for the emission and appearance of the source. We argue that the Galactic Center holds enormous potential for experimental tests of black hole accretion and theories of gravitation in their strong limits.

review paper, 31 pages, 5 figures, includes "Sgr A* fact sheet" table, accepted for Class. Quantum Grav., focus issue on astrophysical black holes (eds. L. Rezzolla & D. Merritt)

References in corpus (22)

• Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
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• Apparent shape of super-spinning black holes
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• An Unambiguous Detection of Faraday Rotation in Sagittarius A*
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• Shadow of a Kaluza-Klein rotating dilaton black hole
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• Using Millimeter VLBI to Constrain RIAF Models of Sagittarius A*
• Testing RIAF model for Sgr A* using the size measurements
• Limits on the Position Wander of Sgr A*
• Flares and variability from Sagittarius A*: five nights of simultaneous multi-wavelength observations
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Cited by in corpus (103)

• First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
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• Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole
• First Sagittarius A* Event Horizon Telescope Results. VI: Testing the Black Hole Metric
• Detection of the Schwarzschild precession in the orbit of the star S2 near the Galactic centre massive black hole
• Shadow of rotating regular black holes
• First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multi-wavelength Observations, Data Processing, and Calibration
• Testing black hole candidates with electromagnetic radiation
• Shadow of five-dimensional rotating Myers-Perry black hole
• A coordinate-independent characterization of a black hole shadow
• Black Hole Parameter Estimation from Its Shadow
• Constraining the spin and the deformation parameters from the black hole shadow
• Slowly-Rotating Black Holes in Einstein-Dilaton-Gauss-Bonnet Gravity: Quadratic Order in Spin Solutions
• Black holes in an Effective Field Theory extension of GR
• BlackHoleCam: fundamental physics of the Galactic center
• Constraints on a charge in the Reissner--Nordström metric for the black hole at the Galactic Center
• Observational appearance of inefficient accretion flows and jets in 3D GRMHD simulations: Application to Sgr~A*
• The Power of Imaging: Constraining the Plasma Properties of GRMHD Simulations using EHT Observations of Sgr A*
• Plasma diagnostic potential of 2p4f in N${}^{+}$ -- accurate wavelengths and oscillator strengths
• Deflection of light by rotating regular black holes using the Gauss-Bonnet theorem
• Sgr A* and General Relativity
• A General Relativistic Null Hypothesis Test with Event Horizon Telescope Observations of the black-hole shadow in Sgr A*
• Radio and Millimeter Monitoring of Sgr A*: Spectrum, Variability, and Constraints on the G2 Encounter
• Asymptotic safety casts its shadow
• Strong gravitational lensing --- A probe for extra dimensions and Kalb-Ramond field
• Energetics and optical properties of $6$-dimensional rotating black hole in pure Gauss-Bonnet gravity
• Testing Rotating Regular Metrics as Candidates for Astrophysical Black Holes
• Testing Rotating Regular Metrics with EHT Results of Sgr A*
• Shadow cast by rotating braneworld black holes with a cosmological constant
• Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum
• Horizon structure of rotating Einstein-Born-Infeld black holes and shadow
• Fermi Bubbles Inflated by Winds Launched from the Hot Accretion Flow in Sgr A*
• Detection of intrinsic source structure at ~3 Schwarzschild radii with Millimeter-VLBI observations of SAGITTARIUS A*
• ALMA Polarimetry of Sgr A*: Probing the Accretion Flow from the Event Horizon to the Bondi Radius
• RAPTOR I: Time-dependent radiative transfer in arbitrary spacetimes
• Strong deflection gravitational lensing by a modified Hayward black hole
• Shadow of a Charged Rotating Non-Commutative Black Hole
• Shadow cast by a rotating charged black hole in quintessential dark energy
• ALMA and VLA measurements of frequency-dependent time lags in Sagittarius A*: evidence for a relativistic outflow
• Pulsars as probes of gravity and fundamental physics
• Gravitational waves from bodies orbiting the Galactic Center black hole and their detectability by LISA
• Shadows of black hole surrounded by anisotropic fluid in Rastall theory
• $f(R)$-gravity after the detection of the orbital precession of the S2 star around the Galactic centre massive black hole
• The Intrinsic Two-Dimensional Size of Sagittarius A*
• The impact of Faraday effects on polarized black hole images of Sagittarius A*
• Imaging an Event Horizon: Mitigation of Source Variability of Sagittarius A*
• Supermassive dark-matter Q-balls in galactic centers?
• Influence of an anisotropic matter field on the shadow of a rotating black hole
• Test of Einstein equivalence principle near the Galactic center supermassive black hole
• Probing the innermost accretion flow geometry of Sgr A* with Event Horizon Telescope
• Silhouettes of invisible black holes
• Gravitational lensing by a Horndeski black hole
• Strong deflection lensing by charged black holes in scalar-tensor gravity
• Event horizon image within black hole shadow
• The Galactic Center as a laboratory for theories of gravity and dark matter
• The black hole at the Galactic Center: observations and models
• Multiwavelength study of the flaring activity of Sgr A* in 2014 February-April
• Quantifying Intrinsic Variability of Sagittarius A* using Closure Phase Measurements of the Event Horizon Telescope
• Visibility of Black Hole Shadows in Low-luminosity AGN
• Sagittarius A* High Energy X-ray Flare Properties During NuSTAR Monitoring of the Galactic Center from 2012 to 2015
• Testing the nature of the supermassive black hole candidate in SgrA* with light curves and images of hot spots
• Asymmetric structure in Sgr A* at 3mm from closure phase measurements with VLBA, GBT and LMT
• Bayesian techniques for comparing time-dependent GRMHD simulations to variable Event Horizon Telescope observations
• A formal method for identifying distinct states of variability in time-varying sources: SgrA* as an example
• Sixteen years of X-ray monitoring of Sagittarius A*: Evidence for a decay of the faint flaring rate from 2013 August, 13 months before a rise in the bright flaring rate
• Numerical black hole initial data and shadows in dynamical Chern-Simons gravity
• MeqSilhouette : A mm-VLBI observation and signal corruption simulator
• Study of the X-ray activity of Sgr A* during the 2011 XMM-Newton campaign
• To see invisible: image of the event horizon within the black hole shadow
• Accretion of a Vlasov gas on to a black hole from a sphere of finite radius and the role of angular momentum
• Simultaneous Monitoring of X-ray and Radio Variability in Sagittarius A*
• Gravitational Lensing of a star by a rotating black hole
• Spherical Skyrmion black holes as gravitational lenses
• The multiwavelength spectrum of NGC 3115: Hot accretion flow properties
• A nonthermal bomb explains the near-infrared superflare of Sgr A*
• Flares and their echoes can help distinguish photon rings from black holes with space-Earth very long baseline interferometry
• Black hole and cosmos with multiple horizons and multiple singularities in vector-tensor theories
• Probing spacetime around Sagittarius A* using modeled VLBI closure phases
• Imaging black holes: past, present and future
• System Design for the Event Horizon Imaging Experiment Using the PECMEO Concept
• The Scales of Gravitational Lensing
• Continuation of the X-ray monitoring of Sgr A*: the increase in bright flaring rate confirmed
• Micro-arcsecond structure of Sagittarius A* revealed by high-sensitivity 86 GHz VLBI observations
• Gravitational lensing by a stable rotating regular black hole
• Images and Spectra of Time Dependent Two Component Advective Flow in Presence of Outflows
• Confronting the jet model of Sgr A* with the Faraday rotation measure observations
• The X-ray footprint of the CircumNuclear Disk
• Some New Possible Anticipated Signals for Existence of Magnetic Monopoles
• Regular scale-dependent black holes as gravitational lenses
• Mid-Infrared studies of dusty sources in the Galactic Center
• A Magnetic-Monopole-Based Mechanism to the formation of the Hot Big Bang Modeled Universe
• The impact of gravitational lensing in the reconstruction of stellar orbits around Sgr A*
• A Multi-Frequency Study of the Milky Way-like Spiral Galaxy NGC 6744
• Image of Quantum Improved Regular Kerr Black Hole and Parameter Constraints from EHT Observations
• A probabilistic approach to phase calibration: I. Effects of source structure on fringe-fitting
• Shadows of a generic class of spherically symmetric, static spacetimes
• Shadow of axisymmetric, stationary and asymptotically flat black holes in the presence of plasma
• The Galactic Center Black Hole Laboratory
• General relativistic quasi-spherical accretion in a dark matter halo
• The Core-shift of Sagittarius A* as a Discriminant between Disk and Jet Emission Models with millimeter-VLBI
• Microlensing Black Hole Shadows
• Visible shapes of black holes M87* and SgrA*
• Beyond Sgr A* and M87*: Sub-Microarcsecond Black Hole Shadow Detection via Lunar-based Extremely Long Baseline Interferometry