Modelling accretion disc and stellar wind interactions: the case of Sgr A

Area of Science:

• Astrophysics
• High-energy astrophysics
• Black hole accretion physics

Background:

• Sagittarius A* (Sgr A*) is a key target for studying low-luminosity accreting systems.
• Interactions between stellar winds from S-cluster stars and Sgr A*'s accretion disk can form shock structures.
• These shock structures are predicted to emit detectable X-rays.

Purpose of the Study:

• To model the geometry of termination shocks formed by stellar wind-accretion disk interactions.
• To investigate the potential for X-ray emission from shocked stellar winds.
• To apply the model to specific astrophysical events, like the passage of S2 star.

Main Methods:

• Developed a semi-analytical model for termination shock geometry.
• Employed numerical hydrodynamic simulations to verify and extend the model.
• Calculated X-ray emission via thermal bremsstrahlung from shocked winds.

Main Results:

• The model describes termination shock geometry and Kelvin-Helmholtz instabilities.
• Simulations confirm the model's predictions for shocked wind behavior.
• Application to S2 star's pericentre passage predicts a month-long X-ray flare.

Conclusions:

• The shocked stellar wind can produce observable X-ray flares comparable to Sgr A*'s quiescent emission.
• Detection of these flares can constrain accretion disk properties near Sgr A*.
• This provides a novel method to probe low-luminosity accretion flows.