First solid evidence of the universal mechanism shaping cosmic jets revealed

An international team, including researchers from the Instituto de Astrofísica de Andalucía (IAA-CSIC), has discovered a universal mechanism that explains how jets—powerful streams of matter and energy—maintain their shape as they travel through space.

This breakthrough was made possible thanks to observations from the Karl G. Jansky Very Large Array (VLA), a highly versatile radio observatory located on the San Agustin Plains, United States.

08/01/2025

Jets are powerful streams of matter and energy observed on a wide range of scales across the universe, from supermassive black holes at the centers of galaxies to protostars—forming stars—within our own Milky Way. Despite the diversity of their energy sources, these jets, which travel at supersonic speeds—sometimes near the speed of light—and play a key role in shaping their environments, are believed to be different manifestations of a single universal phenomenon. However, their collimation mechanism—how they remain so tightly focused without dispersing into space—has remained a mystery for decades.

Now, this study, published in the journal Astrophysical Journal Letters, “provides the first solid evidence of the existence of a helical magnetic field – in the shape of a spiral spring – in a protostellar jet, thus supporting the universality of the jet collimation mechanism in different astrophysical environments,” states Adriana Rodríguez-Kamenetzky, of Institute of Theoretical and Experimental Astronomy (IATE), Argentinian National Scientific and Technical Research Council and National University of Córdoba (CONICET-UNC), who leads the work.

 

Results of the Rotation Measure analysis in the HH80-81 jet. The left image shows the streamline image of the component of the magnetic field parallel to the plane of the sky. In the middle panel, the color scale of the RM indicates the direction of the magnetic field along the line of sight, i.e., red, away from the observer, and blue, towards the observer. The right panel shows a scheme depicting the 3D configuration of the magnetic field, exhibiting a helical topology. Credit: Rodríguez-Kamenetzky et al. 2025, The Astrophysical Journal Letters

 

Image of the radio emission from the jet (white outlines) and the accretion disc (colour scale) of HH 80-81. It shows a region of approximately 5000 au x 10000 au (1 au = distance between the Earth and the Sun). The jet was imaged with the Very Large Array (VLA) and the disc with the Atacama Large Millimeter/submillimeter Array (ALMA). Credit: Guillem Anglada.

 

The finding, based on observations conducted with the Karl G. Jansky Very Large Array (VLA) radio observatory, operated by the National Radio Astronomy Observatory (NRAO) and managed by the U.S. National Science Foundation (NSF), reveals that this helical magnetic field is responsible for guiding these jets in both young stars and supermassive black holes.

“This study required long integration times and a highly intricate data calibration and reduction process, pushing the VLA to the limits of its capabilities,” explains Guillem Anglada, a researcher at the Instituto de Astrofísica de Andalucía (IAA-CSIC) and a member of the team behind the study.

 

A HELICAL MAGNETIC FIELD: THE KEY TO THE MYSTERY

The high sensitivity and broad bandwidth of the upgraded VLA enabled the research team to conduct an unprecedented analysis of the so-called Rotation Measure of synchrotron radiation—a type of electromagnetic emission produced by charged particles moving at high speeds in magnetic fields—from the jet known as HH 80-81, which originates from a young star in our galaxy.

This allowed the researchers to measure the rotation of the polarization angle of the radiation as it passes through a magnetized and ionized medium, known as Faraday rotation, revealing the true orientation of the magnetic field. Using this technique, they confirmed the presence of a helical magnetic field, similar to those detected in jets produced by supermassive black holes in distant active galaxies.

Since HH 80-81 is a much closer jet, its properties could be studied in significantly greater detail.

 

Artist's view of a protostar driving a bipolar jet within a helical magnetic field. Credit: Wolfgang Steffen, UNAM

 

This discovery provides the first clear evidence that jets from young stars and those from distant galaxies share the same mechanism to remain tightly focused.

 

A UNIVERSAL MECHANISM

In 2010, the first-ever map of the magnetic field distribution in a protostellar jet was created, showing the pattern of the field projected onto the sky plane. This discovery already revealed important similarities, though on a much smaller scale, with the jets emerging from the accretion disks around supermassive black holes in active galaxies. "Now, we have taken the next step by mapping not only the magnetic field distribution in the sky plane, but also in the line-of-sight direction, allowing us to obtain its three-dimensional structure," says Guillem Anglada (IAA-CSIC). "In doing so, the similarities with extragalactic jets are even more evident."

 

Artist's conception of a forming star with a dust disc and bipolar jets. Credit: Wolfgang Steffen, UNAM

 

One advantage of studying a protostellar jet is that, being a closer object, it can be observed in much greater detail, providing the research team with information about physical properties that remain unknown in extragalactic jets. Thus, it has been confirmed that the helical magnetic field is intrinsic to the disk-jet system and is not the result of interactions with the surrounding medium.

All these advancements point to the existence of a universal collimation mechanism that could be common to all astrophysical jets, from those of young stars to those of supermassive black holes. "This discovery helps us better understand the fundamental processes that govern the flows of matter and energy in the universe," concludes Guillem Anglada (IAA-CSIC).

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