ALMA Captures the Birthplace of a Magnetized Protostellar Jet for the First Time

Released: 20th August, 2025, Academia Sinica, Institute of Astronomy & Astrophysics (ASIAA), Taiwan

In the universe, stars and planets don’t just appear out of nowhere — their birth is like a long construction project. Around a young star,  there is often a surrounding accretion disk made of gas and dust. Material within this disk continually rotates, clumps together, and eventually falls onto the star, allowing it to grow over time.

However, this process faces a key challenge: if the material in the accretion disk spins too fast, it becomes difficult for it to fall toward the center. Astronomers have long suspected that jets — streams of gas shot out at high speeds from near the star — can carry away the excess rotational energy, making it easier for material to move inward. But the launching points of such jets lie extremely close to the star, tens of times closer than the Earth is to the Sun, and previous observations have not been sufficient to clearly resolve their details or confirm their origins.

An international research team, led by Chin-Fei Lee at Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), has used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe an extremely young protostar system known as HH 211. This protostar is only about 35,000 years old, has just 6% of the Sun’s mass, and lies about 1,000 light-years away. It possesses a bright bipolar jet — and remarkably, this jet is among the very few known examples where a magnetic field has been detected, offering a rare opportunity to test magnetic field–driven ejection models.

The observations show that the jet moves at over 100 kilometers per second, but rotates very slowly, with a specific angular momentum of only 4 au·km/s. Using conservation of angular momentum and energy, the team determined that the jet originates from the innermost edge of the accretion disk, just 0.02 astronomical units from the star — in excellent agreement with the theoretical X-wind model. This model describes how a magnetic field can act like a slingshot to hurl gas outward, and it predicts a magnetic field strength consistent with previous measurements.

This discovery marks the first time the launch point of a magnetized jet has been pinpointed with such high precision, and directly confirms that jets are indeed the “plumbers” of star formation — removing the last bits of angular momentum from the accretion disk so that material can fall smoothly onto the star. In the future, such observations will not only help solve the mystery of how stars are born, but also improve our understanding of the early stages of planet formation — since planets are nurtured within these very same disks.

More Information:

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organization 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 National Science and Technology Council of Taiwan (NSTC), 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.

This research was presented in a paper “A magnetized protostellar jet launched from the innermost disk at the truncation radius” by Lee et al. appeared in Scientific Reports.

The team is composed of Chin-Fei Lee (ASIAA, Taiwan; TARA, Taiwan), Kai-Syun Jhan (ASIAA, Taiwan; National Taiwan University, Taiwan) and Anthony Moraghan (ASIAA, Taiwan; University of Manchester, UK )

Media Contact:

Dr. Chin-Fei Lee, Email: cflee@asiaa.sinica.edu.tw , Tel: +886 2 2366 5445