The research titled Low-angular-momentum Black Hole Accretion: First General Relativistic Magnetohydrodynamic Evidence of Standing Shocks has been published recently in The Astrophysical Journal by Prof. MAO Jirong in Yunnan Observatories, Chinese Academy of Sciences, and other international collaborators. In this research, a standing shock has been found in the low-angular-momentum accretion mode by the general relativistic magnetohydrodynamical (GRMHD) simulations.  

Accretion occurs around compact objects by strong gravity. The physics of accretion is the frontier of high-energy astrophysical research and a key issue in the study of galaxy formation and evolution. Accretion near black hole horizon has been a hot topic since the BH shadow was firstly observed by event horizon telescope (EHT) in 2019. Shock in accretion flow could be formed near the central black hole, and the location is roughly fixed as it is standing shock. However, there has long been debate over whether the standing shock exists in accretion flow.

In this work, the team studied the accretion around black hole using two- and three- dimensional MHD simulations in the framework of general relativity. They found that shock is formed near the central black hole in the low-angular momentum accretion and the location remains unchanged during the accretion. Thus, it has been confirmed that the standing shock does exist in accretion flow. Meanwhile, it has also been found that the standing shock can appear in the standard and normal evolution (SANE) case, but not in the magnetic arrested disk (MAD) case.

As the standing shock oscillates at the same location, it can accelerate particles. These particles produce radiation, which is observed as quasi-periodic Oscillation (QPO) phenomenon. The research on the dynamics of accretion is crucial for further investigating the QPO signals observed in X-ray binaries and active galactic nuclei.

This work is supported by the National Key R&D Program of China, the Natural Science Foundation of China, and the Yunnan Revitalization Talent Support Program.

Figure 1: density distribution. Image by MAO.

Figure 2: identification of standing shock discontinuity. Image by MAO.

Contact:
MAO Jirong
Yunnan Observatories, CAS
E-mail:jirongmao@ynao.ac.cn