The Surprisingly Small Impact of Magnetic Fields On The Inner Accretion Flow of Sagittarius A* Fueled By Stellar Winds

Abstract

We study the flow structure in 3D magnetohydrodynamic (MHD) simulations of accretion onto Sagittarius A* via the magnetized winds of the orbiting Wolf-Rayet stars. These simulations cover over 3 orders of magnitude in radius to reach $\approx$ 300 gravitational radii, with only one poorly constrained parameter (the magnetic field in the stellar winds). Even for winds with relatively weak magnetic fields (e.g., plasma $\beta$ $\sim$ $10^6$), flux freezing/compression in the inflowing gas amplifies the field to $\beta$ $\sim$ few well before it reaches the event horizon. Overall, the dynamics, accretion rate, and spherically averaged flow profiles (e.g., density, velocity) in our MHD simulations are remarkably similar to analogous hydrodynamic simulations. We attribute this to the broad distribution of angular momentum provided by the stellar winds, which sources accretion even absent much angular momentum transport. We find that the magneto-rotational instability is not important because of i) strong magnetic fields that are amplified by flux freezing/compression, and ii) the rapid inflow/outflow times of the gas and inefficient radiative cooling preclude circularization. The primary effect of magnetic fields is that they drive a polar outflow that is absent in hydrodynamics. The dynamical state of the accretion flow found in our simulations is unlike the rotationally supported tori used as initial conditions in horizon scale simulations, which could have implications for models being used to interpret Event Horizon Telescope and GRAVITY observations of Sgr A*.

Accepted by MNRAS; 22 pages; 24 figures, comments welcome

References in corpus (24)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• Athena: A New Code for Astrophysical MHD
• The Two Young Star Disks in the Central Parsec of the Galaxy: Properties, Dynamics and Formation
• An Update on Monitoring Stellar Orbits in the Galactic Center
• An Unambiguous Detection of Faraday Rotation in Sagittarius A*
• Stellar and wind properties of massive stars in the central parsec of the Galaxy
• Galactic Centre stellar winds and Sgr A* accretion
• Observational appearance of inefficient accretion flows and jets in 3D GRMHD simulations: Application to Sgr~A*
• The Disc-Jet Symbiosis Emerges: Modeling the Emission of Sagittarius A* with Electron Thermodynamics
• 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
• Variable accretion and emission from the stellar winds in the Galactic centre
• Event-Horizon-Telescope Evidence for Alignment of the Black Hole in the Center of the Milky Way with the Inner Stellar Disk
• Accretion of cool stellar winds on Sgr A*: another puzzle of the Galactic Centre?
• Large magnetic field variations towards the Galactic Centre magnetar, PSR J1745-2900
• The Intrinsic Two-Dimensional Size of Sagittarius A*
• A Resolution Study of Magnetically Arrested Disks
• Tilted Disks around Black Holes: A Numerical Parameter Survey for Spin and Inclination Angle
• Stellar winds pump the heart of the Milky Way
• The role of feedback in accretion on Low Luminosity AGN: Sgr A* case study
• Nonaxisymmetric Effects in the Black Hole Accretion Inviscid Hydrodynamics: Formation and Evolution of a Tilted Torus
• ALMA Detection of Extreme Blue-Shifted Ionized Gas Within 0.2 pc of Sgr A* from -480 to -300 km/s

Cited by in corpus (43)

• First Sagittarius A* Event Horizon Telescope Results. V. Testing Astrophysical Models of the Galactic Center Black Hole
• Jets in Magnetically Arrested Hot Accretion Flows: Geometry, Power and Black Hole Spindown
• Ab Initio Horizon-Scale Simulations of Magnetically Arrested Accretion in Sagittarius A* Fed by Stellar Winds
• Efficiently Cooled Stellar Wind Bubbles in Turbulent Clouds II. Validation of Theory with Hydrodynamic Simulations
• Star Formation Regulation and Self-Pollution by Stellar Wind Feedback
• Magnetically Modified Spherical Accretion in GRMHD: Reconnection-Driven Convection and Jet Propagation
• Supercritical growth pathway to overmassive black holes at cosmic dawn: coevolution with massive quasar hosts
• GRMHD Simulations and Modeling for Jet Formation and Acceleration Region in AGNs
• Numerical simulations of the random angular momentum in convection II: delayed explosions of red supergiants following "failed'' supernovae
• Magnetized Accretion onto and Feedback from Supermassive Black Holes in Elliptical Galaxies
• Evidence for a jet and outflow from Sgr A*: a continuum and spectral line study
• The intrinsic structure of Sagittarius A* at 1.3 cm and 7 mm
• Two-Temperature GRMHD Simulations of Black Hole Accretion Flows with Multiple Magnetic Loops
• Second Scale Submillimeter Variability of Sagittarius A* during flaring activity of 2019: On the Origin of Bright Near Infrared Flares
• Relative depolarization of the black hole photon ring in GRMHD models of Sgr A* and M87*
• Hunting for wandering massive black holes
• Magnetic Flux Transport in Radiatively Inefficient Accretion Flows and the Pathway towards a Magnetically Arrested Disk
• General relativistic hydrodynamic simulations of perturbed transonic accretion
• Flares and their echoes can help distinguish photon rings from black holes with space-Earth very long baseline interferometry
• Implications from the velocity profile of the M87 jet: a possibility of a slowly rotating black hole magnetosphere
• Multi-wavelength Variability of Sagittarius A* in July 2019
• The Inner 2 pc of Sagittarius A*: Simulations of the Circumnuclear Disk and Multiphase Gas Accretion in the Galactic Center
• The Swansong of the Galactic Center Source X7: An Extreme Example of Tidal Evolution near the Supermassive Black Hole
• Evolution of rotating massive stars with new hydrodynamic wind models
• Magnetic field structure in the vicinity of a super-massive black hole in low luminosity galaxies: the case of Sgr A*
• Upper Limit on Brackett-gamma Emission from the Immediate Accretion Flow onto the Galactic Black Hole
• Magnetically arrested disk flux eruption events to describe SgrA* flares
• Polarized signatures of adiabatically expanding hotspots in Sgr A*'s accretion flow
• Over-massive Central Black Holes in the Cosmological Simulations ASTRID and Illustris TNG50
• The formation and stability of a cold disc made out of stellar winds in the Galactic Centre
• The Effects of Tilt on the Time Variability of Millimeter and Infrared Emission from Sagittarius A*
• Detection of a 20 minute time lag observed from Sgr A* between 8 and 10 GHz with the VLA
• Structure of the super-Eddington outflow and itsimpact on the cosmological scale
• Hydrodynamic Evolution of Sgr A East: The Imprint of A Supernova Remnant in the Galactic Center
• HESS J1745$-$290 spectrum explained by a transition in the diffusion regime of PeV cosmic rays in the Sgr A* accretion flow
• Helical and nonhelical large-scale dynamos in thin accretion discs
• Subsonic Wind Accretion
• Compact stellar systems hosting an intermediate mass black hole: magnetohydrodynamic study of inflow-outflow dynamics
• The Discovery of an Active Wind from the Milky Way's Black Hole
• Tidal phenomena in the Galactic Center: The curious case of X7
• Remarkable correspondence of Sagittarius A* submillimeter variability with a stellar-wind-fed accretion flow model
• Revisiting the Evolutionary Status of Massive Stars at the central parsec of the Milky Way
• PATOKA: Simulating Electromagnetic Observables of Black Hole Accretion