New research is dramatically sharpening our understanding of one of the universe’s most formidable phenomena: the colossal jets of plasma launched from the vicinity of black holes at nearly the speed of light. For decades, the precise mechanisms that power these relativistic jets have been a subject of intense debate. Now, separate, complementary studies are providing a more complete picture, combining unprecedented observational power with advanced theoretical simulations to reveal how black holes, both large and small, act as cosmic engines.
An international team of astronomers has leveraged a global network of radio telescopes to capture the sharpest images yet of the region where these jets are born, while theoretical astrophysicists have developed sophisticated models that simulate the chaotic interplay of magnetic fields and superheated matter under the extreme influence of a black hole’s gravity. Together, these findings are clarifying how a black hole’s rotation can be converted into outflows powerful enough to shape the evolution of entire galaxies, offering solutions to a mystery that dates back to the earliest observations of these strange celestial objects over a century ago.
A Sharper Observational View
To peer into the heart of these cosmic engines, an international collaboration of astronomers utilized the Event Horizon Telescope (EHT). The EHT is not a single instrument but a globe-spanning array of radio telescopes that work in concert, a technique known as Very Long Baseline Interferometry. This network effectively creates a virtual telescope with a diameter equivalent to that of the Earth, providing the extraordinary resolution necessary to resolve features close to a black hole’s event horizon—the point of no return. The team targeted 16 active galactic nuclei (AGNs), which are the luminous, energetic centers of galaxies powered by supermassive black holes actively feeding on surrounding gas and dust.
These observations allowed researchers to probe the structure of the jets closer to their launch point than ever before. The results revealed a consistent geometry: the jets start with a parabolic, or curved, shape near the black hole before transitioning into a more conical, straight-line form as they extend thousands of light-years into space. This structural detail is a crucial clue for theorists, as it constrains the physics of how the jet is initially accelerated and confined. The data for this groundbreaking work came from several key instruments, including the Atacama Large Millimeter/submillimeter Array (ALMA), the Green Bank Telescope, and the Very Large Baseline Array (VLBA).
The Engine of Ejection
While observations define the structure of these jets, theoretical models are required to understand the physics driving them. Researchers at Goethe University Frankfurt developed a new numerical code to simulate the extreme environment around a spinning black hole with immense precision. Their work focused on how the immense rotational energy of a black hole, such as the one at the center of the M87 galaxy, can be extracted and converted into a powerful, focused outflow. M87’s black hole, M87*, contains the mass of 6.5 billion suns and powers a jet that extends 5,000 light-years into space.
Magnetic Field Dynamics
The simulations confirm the critical role of magnetic fields, which become twisted and amplified by the black hole’s powerful spin and the swirling accretion disk of infalling matter. This process is central to the long-standing Blandford-Znajek mechanism, a leading theory for how jets are powered. However, the new simulations reveal a more complex and dynamic process at the black hole’s equator. They show intense magnetic reconnection, an event where magnetic field lines violently break and reassemble.
This reconnection converts magnetic energy into heat, radiation, and kinetic energy, accelerating particles in energetic “bubbles” of plasma known as plasmoids. According to the researchers, this process creates a chain of these plasmoids, which are then ejected outwards at relativistic speeds, contributing to the overall jet. This suggests that the Blandford-Znajek mechanism may not be the only process at play, with magnetic reconnection providing another powerful way to tap the black hole’s rotational energy.
A Universal Phenomenon
While much of the focus has been on supermassive black holes at the centers of galaxies, similar jets are produced by smaller, stellar-mass black holes, which form from the collapse of massive stars. For a long time, it was thought that the jets from these smaller black holes were less powerful and slower than their supermassive counterparts. However, new research is challenging this assumption. A recent study of a stellar-mass black hole in the X-ray binary system 4U 1543-47 used radio interferometry to track ejections during a single outburst.
The measurements revealed that the material was launched with a Lorentz factor—a measure of its speed relative to the speed of light—of at least 4.6 and likely around 8. This demonstrates that stellar-mass black holes can produce jets that are just as relativistic as those from the supermassive black holes found in active galactic nuclei. This finding is significant because stellar-mass systems evolve on much faster, human-observable timescales, allowing astronomers to study the full cycle of jet launching and quenching in detail, providing insights that can be applied across all mass scales.
Cosmic Architecture and Influence
The formation of these powerful jets is not an isolated event but is tied to the broader cosmic environment. One critical factor appears to be the history of the host galaxy. A 2015 study using the Hubble Space Telescope found a strong link between the presence of relativistic jets and galaxies that have undergone a merger with another galaxy. The astronomers observed that nearly all galaxies with powerful radio emissions indicating strong jets showed evidence of a recent or ongoing merger.
However, the study also found that a merger alone is not sufficient to guarantee a jet. About 40% of the other galaxies studied had also experienced mergers yet failed to produce powerful radio jets. This suggests that while a galactic merger is likely a necessary condition—perhaps by disrupting the gas dynamics and funneling large amounts of fuel toward the central black hole—other factors, such as the black hole’s spin, are also required. Once launched, these jets have a profound impact on their surroundings. They pump vast amounts of energy and matter into the interstellar and intergalactic medium, which can regulate the rate of star formation within the host galaxy and influence its overall evolution.