A researcher at the Shanghai Astronomical Observatory (SHAO), Chinese Academy of Sciences (CAS), Chun Xu, proposed a new theory for accretion disk and jet formation, unifying the jet formation mechanisms of Active Galactic Nuclei (AGN), X-ray Binaries (XRB), and Young Stellar Objects (YSO) under a model based on the turbulent Advection-Dominated Accretion Flow (turbulent ADAF). The results were published online on June 29, 2026, in Monthly Notices of the Royal Astronomical Society.

Jets are extremely spectacular astronomical phenomena, observed in Active Galactic Nuclei, X-ray Binaries, Young Stellar Objects, and other celestial bodies. Currently, different jet formation theories exist for different objects, including the Blandford–Znajek mechanism and the magnetocentrifugal mechanism represented by Blandford–Payne and X-wind. The newly proposed turbulent ADAF theory can unify the jet formation across different objects within a purely hydrodynamic framework that does not depend on magnetic fields.

A Unified Model for Jet Formation

Assuming that the released gravitational potential energy can be temporarily stored in turbulence, the accretion disk near the central object can transition into a turbulent ADAF. This is similar to the Narayan-Yi ADAF but with a higher density and remains optically thick. A funnel-like structure forms at the center of the disk, facilitating jet escape. The turbulent ADAF does not require the two-temperature plasma assumption of the classical ADAF and can be applied to accretion flows of different objects.

The acceleration mechanism is another core issue that the jet model needs to address. According to standard thick-disk theory, the thickness of the accretion disk is related to the equipotential pressure, which can be converted using turbulent pressure. In the new theory, a parameter η is defined, representing the ratio of turbulent energy within the accretion disk to the local Keplerian energy, with 0 ≤ η < 1. The jet energy comes from three parts: first, the Keplerian rotational energy E_K of the standard thin disk; second, the random turbulent clump velocity deviating from the Keplerian velocity, with an average energy ηE_K; and third, the acceleration energy caused by the pressure difference between the middle and outer edges of the thick disk, also on the order of ηE_K. Therefore, near the central object, some turbulent clumps can be accelerated to (1+2η)E_K. As long as η > 0.5, the total energy of these turbulent clumps becomes positive, allowing them to escape through the funnel-like structure and form jets. This model does not depend on whether the central object is a black hole or a star; it relies solely on the accretion disk itself, making it applicable to various objects with jets, such as AGN, XRB, and YSO.

This model makes several basic qualitative predictions for jets: (1) An inner thick disk (i.e., η > 0.5) is a fundamental condition for jet formation; (2) Jets originate from the innermost region of the thick accretion disk adjacent to the central object; (3) The geometrically thick turbulent ADAF disk is also optically thick; (4) Jets are a collective effect of numerous high-velocity small clumps; (5) Jet material comes directly from the accretion disk and consists of ordinary baryonic matter.

Comparison with Observations of Different Objects

The AGN M87 is qualitatively consistent with the predictions of this model, with jets originating from near the black hole at the innermost part of the accretion disk, and the edge-brightened structure of the jet is also consistent with the model. The YSO HH 211 exhibits multi-layered CO and SiO jets perpendicular to the accretion disk, and analysis indicates that the jets originate from the innermost region of the disk, which is also qualitatively consistent with the model. For XRBs, observations show that jet phenomena occur exclusively in the low-hard state corresponding to the thick disk, rather than in the high-soft state corresponding to the thin disk, which is consistent with the model. From black holes in AGN to black holes or neutron stars in XRBs, to ordinary young stars, the astrophysical environments and temperatures vary enormously, and the central object masses differ by millions of times; nevertheless, their jet phenomena are qualitatively consistent with the model's predictions.

Due to the complexity of turbulence, the model is currently in a semi-quantitative state and cannot yet accurately predict observable parameters such as jet intensity and energy spectra. Future work will mainly focus on two aspects: first, comprehensive and detailed theoretical analysis and computer simulations; second, multi-wavelength comprehensive observations of specific sources, or re-analysis of existing data for comparison with the model.

Extensions of the Model

The proposed jet model, especially the turbulent ADAF model, has broad applications in X-ray Binary systems and Active Galactic Nuclei. This model can explain not only the outburst phenomena of black hole X-ray Binaries and the formation mechanism of the spectral index law, but also the inner-disk truncation debate in the hard state of the well-known object GX 339-4, and the origin of the 35-day period of the X-ray Binary Her X-1. It can also explain the formation mechanism of Changing-Look AGN and the classification phenomena of Active Galactic Nuclei. In particular, phenomena such as jet formation, turbulent ADAF size, X-ray Binary outbursts, Changing-Look AGN, and AGN classification are all determined by the dimensionless parameter η and its variations. Preprints related to the model extensions have been placed on the arXiv platform.

arXiv:2603.10311: A variable ADAF disk model for X-ray binary systems
arXiv:2603.28666: Variable ADAF disk as the origin of Changing-Look AGN

This research was supported by the China Manned Space Station Project.

DOI: https://doi.org/10.1093/mnras/stag1236
Scientific Contact: Chun Xu, chun.xuu@shao.ac.cn