December 23, 2024

Unveiling the Magnetic Mysteries of Black Holes: How Does “MAD” Accretion Form Around a Black Hole?

These findings were published in Science on Aug. 31.
The research study was led by Assoc. Prof. You Bei from Wuhan University, Prof. Cao Xinwu from Zhejiang University, and Prof. Yan Zhen from the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences.
Multi-wavelength light curves (revealing the change in brightness gradually) of the black hole X-ray binary MAXI J1820 +070. Credit: SHAO
The process of a great void capturing gas is understood as “accretion”, and the gas falling under the black hole is described as an accretion circulation. The viscous processes within the accretion flow efficiently launch gravitational prospective energy, with a portion of the energy being converted into multi-wavelength radiation. This radiation can be observed by ground-based and area telescopes, permitting us to “see” the great void.
However, there are “unseen” magnetic fields around the black hole. As the great void accretes gas, it likewise drags the electromagnetic field inwards. Previous theories recommended that as the accreting gas continually generates weak external electromagnetic fields, the magnetic field gradually reinforces towards the inner area of the accretion flow. The external magnetic force on the accretion flow increases and neutralizes the inward gravitational pull from the great void. Therefore, in the inner region of the accretion circulation near the great void, when the magnetic field reaches a specific strength, the accreted matter ends up being caught by the magnetic field and can not easily fall into the black hole. This phenomenon is known as a magnetically arrested disk.
The MAD theory was proposed several years ago and has effectively discussed some observational phenomena connected to great void accretion. Nevertheless, no direct observational evidence for the existence of a MAD was readily available, and MAD development and magnetic transport mechanisms stayed secrets.
Schematic representation of accretion circulation, electromagnetic field, and jet advancement. Credit: SHAO
In addition to the supermassive black holes at the centers of almost every galaxy, there are also much more stellar-mass great voids in the universe. Astronomers have actually found stellar-mass black holes in many binary star systems in the Milky Way. These great voids generally have a mass about 10 times that of the Sun. Many of the time, these black holes remain in a quiescent state, releasing incredibly weak electromagnetic radiation. Nevertheless, they sometimes go into an outburst duration that can last for a number of months or even years, producing intense X-rays. As a result, these types of binary star systems are often described as black hole X-ray binaries.
In this research study, the scientists carried out a multi-wavelength information analysis of the outburst of the great void X-ray binary MAXI J1820 +070. They observed that the tough X-ray emission displayed a peak that was followed by a peak in radio emission 8 days later on. Such a long delay between radio emission from the jet and the tough X-rays from the hot accretion circulation is unmatched.
These observations suggest that the weak magnetic field in the external region of the accretion disk is brought into the inner area by the hot gas, and the radial level of the hot accretion flow quickly broadens as the accretion rate decreases. The greater the radial extent of the hot accretion flow, the higher the increase in the magnetic field. This results in a rapid strengthening of the magnetic field near the great void, resulting in the development of a MAD approximately eight days after the peak of the tough X-ray emission.
” Our study for the very first time reveals the procedure of magnetic field transportation in the accretion circulation and the process of MAD formation in the vicinity of the black hole. This represents the direct observational evidence for the existence of a magnetically apprehended disk,” stated Assoc. Prof. You Bei, very first author and co-corresponding author of the study.
Additionally, the research group observed an unmatched delay (about 17 days) between the optical emission from the external region of the accretion circulation and the tough X-rays from the hot accretion circulation. Through numerical simulations of the outburst of the great void X-ray binary, it was discovered that as the outburst approaches the end, the irradiation of hard X-rays causes more accreting product from the far outer region to fall towards the black hole due to instability. This causes an optical flare in the outer area of the accretion flow, with the peak taking place about 17 days after the peak of the difficult X-rays from the hot accretion flow.
” Due to the universality of great void accretion physics, where accretion processes for black holes of different mass scales follow the exact same physical laws, this research study will advance the understanding of scientific concerns associated with massive magnetic field development, jet powering, and velocity mechanisms for accreting great voids of various mass scales,” stated Prof. Cao Xinwu, co-corresponding author of the study.
Similar phenomena to those observed in MAXI J1820 +070 are anticipated to be observed in more accreting great void systems in the near future, kept in mind Prof. Yan Zhen, co-corresponding author of the study.
Recommendation: “Observations of a great void x-ray binary suggest formation of a magnetically apprehended disk” by Bei You, Xinwu Cao, Zhen Yan, Jean-Marie Hameury, Bozena Czerny, Yue Wu, Tianyu Xia, Marek Sikora, Shuang-Nan Zhang, Pu Du and Piotr T. Zycki, 31 August 2023, Science.DOI: 10.1126/ science.abo4504.

The procedure of a black hole catching gas is known as “accretion”, and the gas falling into the black hole is referred to as an accretion circulation. The outward magnetic force on the accretion circulation boosts and combats the inward gravitational pull from the black hole. In the inner region of the accretion flow near the black hole, when the magnetic field reaches a particular strength, the accreted matter ends up being trapped by the magnetic field and can not freely fall into the black hole. In addition to the supermassive black holes at the centers of nearly every galaxy, there are also many more stellar-mass black holes in the universe. Through numerical simulations of the outburst of the black hole X-ray binary, it was found that as the outburst approaches the end, the irradiation of hard X-rays triggers more accreting material from the far outer region to fall toward the black hole due to instability.

An illustration of the great void X-ray binary MAXI J1820 +070 with a magnetically jailed disk formed around the black hole. Credit: You Bei
For the first time, a global team of researchers has actually revealed the magnetic field transportation processes in the accretion circulation of a black hole, in addition to the creation of a magnetically arrested disk, or “MAD,” near the black hole.
This development came from multi-wavelength observations of an outburst occasion from the great void X-ray binary referred to as MAXI J1820 +070. The group utilized Chinas inaugural X-ray astronomical satellite, Insight-HXMT, in addition to several other telescopes for their study.
Key to their discovery was the observation that the radio emission from the great void jet and the optical emission from the outer region of the accretion flow drags the hard X-rays from the hot gas in the inner region of the accretion flow (i.e., the hot accretion circulation) by about eight days and 17 days, respectively.