Free Astronomy Magazine November-December 2025

49 NOVEMBER-DECEMBER 2025 to play a crucial role in how disks evolve and create planets, but until now, no one had been able to un- ambiguously map their presence and structure directly in a disk like TW Hya’s. Previous searches looked for magnetic fields by detecting specific patterns of polarized light, but those signals are exceedingly faint and easily lost amid other ef- fects. Teague and colleagues exam- ined the broadening of specific radio signals—the fingerprints of molecules swirling in the disk— measured by ALMA. By decoding subtle changes in light from the CN molecule, the team could spot the signature widening caused by mag- netic field interactions, a phenome- non known as the Zeeman Effect. The scientists’ analysis revealed magnetic fields as strong as 10 mil- ligauss—a thousand times weaker than a refrigerator magnet, but im- mense on planet-forming scales— threading the disk between 60 and 120 astronomical units (AU) from the star (one AU is the distance from Earth to the Sun). Intriguingly, the field’s structure changes at a lo- cation where a prominent gap slices through the disk, suggesting a di- rect link between magnetic activity and the sculpting of planet-forming regions. “The presence and pattern of these fields look remarkably like the kind that may have threaded the solar nebula as our own planets were forming,” said Teague, “This is the best look we’ve ever had at the invisible hand shaping the birth- places of new worlds.” This ap- proach opens a new window onto questions that have puzzled scien- tists for decades: how do magnetic fields drive the evolution of disks? How do they influence which plan- ets form and where? As telescopes and instruments grow more sensi- tive, astronomers hope to apply these techniques to many more disks. “We are entering an era where we can finally see the mag- netic blueprints that help build new planetary systems,” adds Teague. Improvements to ALMA, like the up- coming Wideband Sensitivity Up- grade, have been designed to do exactly this, “Our findings show that what has been promised with the upgrade will be possible on a grand scale.” This research is a major leap toward understanding not just how planets form around other stars, but how our own cosmic neighborhood came to be. ! T his artist's impres- sion of magnetic fields threading TW Hydrae’s protoplane- tary disk shows a change in morphol- ogy as they encounter gaps and structures in the disk, suggesting a direct link between magnetic fields and the sculpting of planet-forming re- gions. [NSF/AUI/NSF NRAO/M. Weiss]