Helical Magnetic Fields: A Universal Mechanism for Jet Collimation?

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. Hi-Res File

Artistic view of a protostar driving a bipolar jet within a helical magnetic field.
Credit: Wolfgang Steffen, UNAM. Hi-Res File

---

New observations from the National Science Foundation National Radio Astronomy Observatory’s (NSF NRAO) Karl G. Jansky Very Large Array (NSF VLA) provide compelling evidence supporting a universal mechanism for the collimation of astrophysical jets, regardless of their origin. A new study, published in the Astrophysical Journal Letters , reveals the presence of a helical magnetic field within the HH 80-81 protostellar jet, a finding that mirrors similar structures observed in jets emanating from supermassive black holes.

Jets, powerful, highly collimated outflows of matter and energy, are observed across a vast range of scales in the universe. From the supermassive black holes at the centers of galaxies to the young stars in our own Milky Way, these jets play a crucial role in the evolution of their host systems. However, the precise mechanism that guides these jets and prevents them from dispersing into space has remained a long-standing puzzle.

“This is the first solid evidence that helical magnetic fields can explain astrophysical jets at different scales, supporting universality of the collimation mechanism”, said 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) and leader of the work.

Previous research using the NSF VLA, highlighted by NSF NRAO press releases in 2010 and 2021, showed the existence of magnetic fields in some protostellar jets and established the importance of helical magnetic fields in collimating jets from supermassive black holes. However, until now, definitive evidence confirming the presence of helical magnetic fields in protostellar jets had been elusive.  The challenge lies in the fact that the emission from protostellar jets is predominantly thermal, making it difficult to trace the magnetic field structures.

“Back in 2010, we used VLA to detect non-thermal emission and the presence of a magnetic field, but we couldn’t study its 3D structure”, said Carlos Carrasco-González, of the Institute of Radio Astronomy and Astrophysics (IRyA) of the National Autonomous University of Mexico (UNAM).

This new study overcomes these limitations by utilizing the enhanced capabilities of the upgraded NSF VLA. The high sensitivity and broad bandwidth of the NSF VLA allowed astronomers to perform an unprecedentedly detailed Rotation Measure (RM) analysis of the HH 80-81 jet. The RM analysis allows researchers to correct for Faraday rotation – the rotation of the polarization of light as it passes through a magnetized plasma – revealing the true orientation of the magnetic field.

“For the first time, we were able to study the 3D configuration of the magnetic field in a protostellar jet”, said Alice Pasetto, of IRyA-UNAM.

This groundbreaking analysis produced the following key results:

• First-ever RM analysis of a protostellar jet:
  
  This study marks the first time RM analysis has been successfully applied to a protostellar jet, providing a unique insight into its three-dimensional magnetic structure.


• Evidence for a helical magnetic field:
  The analysis definitively reveals a helical magnetic field configuration within the HH 80-81 jet. This result mirrors observations of helical magnetic fields in extragalactic jets, strongly suggesting a common mechanism for jet collimation across vastly different scales.


• Confirmation of universality:
  By analyzing both the approaching jet and the receding counterjet – a feature readily observable in protostellar jets, unlike those originating from supermassive black holes – researchers confirmed that the helical magnetic field is intrinsic to the disk-jet system and not a result of interactions with the surrounding medium.

These findings provide robust support for the hypothesis that helical magnetic fields are a universal mechanism for collimating astrophysical jets, regardless of the scale or origin of the jet. This unifying theory helps unravel the complex physics governing the launch and evolution of these important cosmic structures.

Adriana Rodríguez-Kamenetzky and Alice Pasetto worked with Carlos Carrasco-González and Luis Felipe Rodríguez (IRyA-UNAM) in collaboration with scientists from the Spanish National Research Council (CSIC), the Institute of Space Sciences (ICE-CSIC), the Institute of Space Studies of Catalonia (IEEC), the University of Jaén (Spain) and the Indian Institute of Space Science and Technology (IIST).

Source: National Radio Astronomy Observatory (NRAO)/News

---

About NRAO

The NSF National Radio Astronomy Observatory (NSF NRAO) is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

For media inquiries or further information, please contact:

NRAO Media Contact:

Corrina C. Jaramillo Feldman
Public Information Officer – New Mexico
Tel: +1 505-366-7267
cfeldman@nrao.edu

---

ALMA Spots Metamorphosing Aged Star

ALMA image of the old star system W43A. The high velocity bipolar jets ejected from the central aged star are seen in blue, low velocity outflow is shown in green, and dusty clouds entrained by the jets are shown in orange. Credit: ALMA (ESO/NAOJ/NRAO), Tafoya et al.

Artist’s impression of W43A based on the ALMA observation results. Diffuse spherical gas was emitted from the star in the past. W43A has just started ejecting bipolar jets which entrain the surrounding material. Bright spots in radio emissions from water molecules are distributed around the interface of the jets and the diffuse gas. Credit: NAOJ.

An international team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) captured the very moment when an old star first starts to alter its environment. The star has ejected high-speed bipolar gas jets which are now colliding with the surrounding material; the age of the observed jet is estimated to be less than 60 years. These are key features to understand how the complex shapes of planetary nebulae are formed.

Sun-like stars evolve to puffed-up Red Giants in the final stage of their lives. Then, the star expels gas to form a remnant called a planetary nebula. There is a wide variety in the shapes of planetary nebulae; some are spherical, but others are bipolar or show complicated structures. Astronomers are interested in the origins of this variety, but the thick dust and gas expelled by an old star obscure the system and make it difficult to investigate the inner-workings of the process.

To tackle this problem, a team of astronomers led by Daniel Tafoya in Chalmers University of Technology, Sweden, pointed ALMA at W43A, an old star system in the constellation Aquila, the Eagle.

Thanks to ALMA’s high resolution, the team obtained a very detailed view of the space around W43A. “The most notable structures are its small bipolar jets,” says Tafoya, the lead author of the research paper published by the Astrophysical Journal Letters. The team found that the velocity of the jets is as high as 175 km per second, which is much higher than previous estimations. Based on this speed and the size of the jets, the team calculated the age of the jets to be less than a human life-span.

“Considering the youth of the jets compared to the overall lifetime of a star, it is safe to say we are witnessing the ‘exact moment’ that the jets have just started to shove through the surrounding gas,” explains Tafoya. “When the jets carve through the surrounding material in some 60 years, a single person can watch the progress in their life.”

In fact, the ALMA image clearly maps the distribution of dusty clouds entrained by the jets, which is telltale evidence that it is impacting on the surroundings.

The team assumes that this entrainment is the key to form a bipolar-shaped planetary nebula. In their scenario, the aged star originally ejects gas spherically and the core of the star loses its envelope. If the star has a companion, gas from the companion pours onto the core of the dying star, and a portion of this new gas forms the jets. Therefore, whether or not the old star has a companion is an important factor to determine the structure of the resulting planetary nebula.

“W43A is one of the peculiar so called ‘water fountain’ objects,” says Hiroshi Imai at Kagoshima University, Japan, a member of the team. “Some old stars show characteristic radio emissions from water molecules. We suppose that spots of these water emissions indicate the interface region between the jets and the surrounding material. We named them ‘water fountains,’ and it could be a sign that the central source is a binarity system launching a new jet.”

“There are only 15 ‘water fountain’ objects identified to date, despite the fact that more than 100 billion stars are included in our Milky Way Galaxy,” explains José Francisco Gómez at Instituto de Astrofísica de Andalucía, Spain. “This is probably because the lifetime of the jets is quite short, so we are very lucky to see such rare objects.”

---

Additional Information

These observation results were presented in D. Tafoya et al. “Shaping the envelope of the asymptotic giant branch star W43A with a collimated fast jet” published by the Astrophysical Journal Letters on February 13, 2020.

The research team members are Daniel Tafoya (Calmers University of Technology), Hiroshi Imai (Kagoshima University), José F. Gómez (Instituto de Astrofísica de Andalucía, CSIC), Jun-ichi Nakashima (Sun Yat-sen University), Gabor Orosz (University of Tasmania/Xinjiang Astronomical Observatory), and Bosco H. K. Yung (Nicolaus Copernicus Astronomical Center)

This research was supported by MEXT KAKENHI (No. 16H02167), the Invitation Program for Foreign Researchers of the Japan Society for Promotion of Science (JSPS grant S14128), MINECO (Spain) Grant AYA2017-84390-C2-R (co-funded by FEDER), State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award for the Instituto de Astrofisica de Andalucía (SEV-2017-0709), Australian Research Council Discovery project DP180101061 of the Australian government, CAS LCWR 2018-XBQNXZ-B-021, and National Key R&D Program 2018YFA0404602 of China.

The original press release was published by the National Astronomical Observatory of Japan (NAOJ), an ALMA partner on behalf of East Asia.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

Scientific Paper

---

Contacts

Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
Email: nicolas.lira@alma.cl

Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory
, Tokyo - Japan
Phone: +81 422 34 3630
Email: hiramatsu.masaaki@nao.ac.jp

Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Phone: +49 89 3200 6670
Email: pio@eso.org

Iris Nijman
News and Public Information Manager
National Radio Astronomy Observatory Charlottesville, Virginia - USA
Cell phone: +1 (434) 249 3423
Email: inijman@nrao.edu

Source: Atacama Large Millimeter/submillimeter Array (ALMA)

---