Astronomers have created a detailed map revealing the magnetic fields weaving through TW Hydrae, one of the closest known stars with a planet-forming disk, using the Atacama Large Millimeter/submillimeter Array (ALMA). Led by Dr. Richard Teague at MIT, this new research sheds light on the invisible forces shaping new planets, like those that formed our own solar system over 4.5 billion years ago.
Planets originate in swirling disks of gas and dust that encircle young stars. While telescopes have revealed the shapes and gaps in these disks, scientists have struggled to measure magnetic fields, the unseen agents that guide and sculpt planet-forming material. Magnetic fields are widely thought to play a crucial role in how disks evolve and create planets, but until now, no one had been able to unambiguously 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 effects. Teague and colleagues examined 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 magnetic field interactions, a phenomenon known as the Zeeman Effect.
The scientists’ analysis revealed magnetic fields as strong as 10 milligauss—a thousand times weaker than a refrigerator magnet, but immense 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 location where a prominent gap slices through the disk, suggesting a direct 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 birthplaces of new worlds.”
This approach opens a new window onto questions that have puzzled scientists for decades: how do magnetic fields drive the evolution of disks? How do they influence which planets form and where? As telescopes and instruments grow more sensitive, astronomers hope to apply these techniques to many more disks. “We are entering an era where we can finally see the magnetic blueprints that help build new planetary systems,” adds Teague. Improvements to ALMA, like the upcoming Wideband Sensitivity Upgrade, 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.
About NRAO
The National Radio Astronomy Observatory (NRAO) is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
About ALMA
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (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 (NSTC) in Taiwan 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.