Free Astronomy Magazine November-December 2025

27 NOVEMBER-DECEMBER 2025 streams of gas ejec- ted at high speeds from near the star — can carry away the excess rotational en- ergy, thereby easing the inward move- ment of material. However, the launch- ing points of these jets are extremely close to the star, only tens of times closer than Earth is to the Sun, and previous ob- servations have not been sufficient to re- solve their details or clearly determine their origins. An international research team led by Chin-Fei Lee at the Academia Sinica Institute of Astronomy and Astro- physics (ASIAA) used the Atacama Large Millimeter/submillimeter Ar- ray (ALMA) in Chile to observe an extremely young protostar system called HH 211. This protostar is only about 35,000 years old, has just 6% of the Sun’s mass, and is located ap- proximately 1,000 light-years away. It features a bright bipolar jet, and notably, this jet is one of the few known examples where a magnetic field has been detected, providing a rare opportunity to test models of magnetic-field–driven ejection. The observations reveal 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 [this unit measures how many astronomical units an object travels in one second]. Using conservation of angular momentum and energy, the team determined that the jet originates from the in- nermost edge of the accretion disk, just 0.02 astronomical units from the star — in excellent agreement with the theoretical X-wind model. This model explains how a magnetic field can act like a slingshot to propel gas outward, and it predicts a magnetic field strength consistent with previ- ous measurements. This discovery marks the first time the launch point of a magnetized jet has been identified with such high precision, directly confirming that jets are truly the “plumbers” of star formation—removing the last bits of angular momentum from the ac- cretion disk so material can fall smoothly onto the star. In the fu- ture, these observations will not only help solve the mystery of how stars form but also enhance our un- derstanding of the early stages of planet formation, since planets de- velop within these same disks. ! H H 211 Jet and Outflow Observed by JWST and ALMA. (a) The JWST compos- ite image (in color, Ray et al. 2023) reveals the jet and outflow traced by H ₂ and CO emission lines in the near-infrared. However, thick dust around the pro- tostar blocks JWST’s view of the jet structures within about 1,000 astronomical units. (b) In contrast, ALMA’s CO image in the submillimeter band (shown in grayscale) penetrates this obscured region, clearly unveiling the jet being launched from the accretion disk (green). [Lee et al.]