English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We study the flow structure in 3D magnetohydrodynamic (MHD) simulations ofaccretion onto Sagittarius A* via the magnetized winds of the orbitingWolf-Rayet stars. These simulations cover over 3 orders of magnitude in radiusto reach $\approx$ 300 gravitational radii, with only one poorly constrainedparameter (the magnetic field in the stellar winds). Even for winds withrelatively weak magnetic fields (e.g., plasma $\beta$ $\sim$ $10^6$), fluxfreezing/compression in the inflowing gas amplifies the field to $\beta$ $\sim$few well before it reaches the event horizon. Overall, the dynamics, accretionrate, and spherically averaged flow profiles (e.g., density, velocity) in ourMHD simulations are remarkably similar to analogous hydrodynamic simulations.We attribute this to the broad distribution of angular momentum provided by thestellar winds, which sources accretion even absent much angular momentumtransport. We find that the magneto-rotational instability is not importantbecause of i) strong magnetic fields that are amplified by fluxfreezing/compression, and ii) the rapid inflow/outflow times of the gas andinefficient radiative cooling preclude circularization. The primary effect ofmagnetic fields is that they drive a polar outflow that is absent inhydrodynamics. The dynamical state of the accretion flow found in oursimulations is unlike the rotationally supported tori used as initialconditions in horizon scale simulations, which could have implications formodels being used to interpret Event Horizon Telescope and GRAVITY observationsof Sgr A*.

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