Researchers from Japan have identified changes in X-ray emissions that could help predict when black holes are likely to eject powerful jets of particles and high-energy radiation. The warning signs, observed up to 10 days before jet ejections, could give astronomers valuable time to prepare follow-up observations.
The study, led by the University of Toyama in collaboration with Nagoya University, examined four black hole binary systems. The findings were published in The Astrophysical Journal on November 5, 2026.
Black holes are known for pulling surrounding matter inward, but they can also produce powerful jets that travel through space at speeds approaching that of light. Understanding what triggers these ejections remains a major challenge in astrophysics.
Changes in Accretion Disks May Provide Early Warning Signs
Matter drawn towards a black hole forms an accretion disk, where gas heats up as it spirals inward and emits X-rays. Researchers have previously observed changes in these X-ray emissions before jet ejections, including alterations in the X-ray spectrum and reductions in variability.
However, these observations have not consistently provided enough information to predict when a jet will emerge.
To investigate the possibility of more reliable forecasting, a team led by Professor Toshihiro Kawaguchi of the University of Toyama analysed archived X-ray and radio observations from four black hole binary systems.
The research built on a 2025 study of XTE J1859+226, which suggested that jets could be launched when the inner edge of an accretion disk rapidly moves towards the innermost stable circular orbit (ISCO). This is the closest orbit around a black hole in which matter can maintain a stable circular path.
The latest investigation examined three additional systems: XTE J1550-564, GX 339-4, and MAXI J1820+070.
Four Black Hole Systems Reveal a Common Pattern
The researchers tracked three main parameters: the inner radius of the accretion disk, changes in X-ray variability, and the rate at which gas flows towards the black hole.
They compared these measurements with radio observations, using radio flares as indicators of jet ejection activity.
The analysis revealed a recurring pattern across all four systems. The inner radius of the accretion disk and X-ray variability both decreased approximately one to 10 days before a jet ejection.
However, the researchers did not observe any major increase in the rate of gas flowing towards the black holes.
Another important finding concerned the Eddington limit, which represents the theoretical threshold at which the outward pressure of radiation balances the inward pull of gravity.
In two of the four systems, jets formed when the gas flow rate was below this threshold. This challenges models that explain jet ejections primarily through unusually high accretion rates.
Researchers Propose a Black Hole Jet Forecasting System
The findings suggest that monitoring changes in the accretion disk’s inner radius could help astronomers anticipate jet ejections.
“Monitoring of Rin seems to be suitable for predicting the timing of jet ejections,” said Professor Kawaguchi.
The research team proposes developing an alert system that would notify astronomers when the inner radius and X-ray variability continue to decline, particularly as the disk approaches the ISCO.
Such alerts could provide an observation window ranging from several hours to several days, allowing researchers to coordinate telescope facilities and collect data around the expected time of an ejection.
“The development of a ‘jet forecast’ would enable us to concentrate observing facilities on the expected timing of jet ejections, thereby accelerating our understanding of jet physics,” Professor Kawaguchi added.
Understanding the Wider Effects of Black Hole Jets
Predicting jet ejections could help scientists investigate the physical processes responsible for some of the universe’s most energetic phenomena.
These jets release high-energy photons and particles, including neutrinos and cosmic rays, which can travel across vast distances and interact with their surroundings.
“Jet ejections in the Universe produce high-energy photons and particles, such as neutrinos, and such cosmic rays have long influenced the evolution of living creatures on Earth, including human beings,” Professor Kawaguchi said.
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