The Atacama Large Millimeter/submillimeter Array (ALMA) continues to unravel the mysteries of planetary system formation with its latest groundbreaking observation of HL Tauri, a young star located 480 light-years away. Surrounded by a protoplanetary disk, HL Tauri provides a captivating glimpse into the intricate dance of gas and dust from which planets emerge.
ALMA’s high-resolution image of HL Tauri, one of its initial captures, revealed visible gaps in the protoplanetary disk—potential cradles for emerging protoplanets. To delve deeper into the complexities of planetary formation, a recent study led by Ian Stephens has delivered an unparalleled polarization image of HL Tauri.
This achievement is no small feat; it is based on ten times more polarization measurements than any other disk and a staggering 100 times more than most disks studied to date. Published in Nature on November 15, the study showcases a polarization image of unprecedented depth, offering a close-up view of the subtle patterns within the disk.
Captured at a remarkable resolution of 5 astronomical units (AU)—roughly the distance from the sun to Jupiter—the image reveals intricate details about the orientation of light waves emitted by the dust grains within the disk. The study emphasizes that understanding the polarization of these dust grains is crucial for unraveling the enigma of planetary system evolution.
Dust grains, often non-spherical, exhibit diverse shapes, from oblate to prolate. When light interacts with these grains, it becomes polarized, meaning the waves align in a specific direction. The new findings from ALMA suggest that the dust grains in HL Tauri’s disk behave more like prolate grains, shedding light on their size and shape.
A surprising revelation from the study is the prevalence of polarization within the gaps of the disk, surpassing that of the rings, despite the latter containing more dust. This difference suggests that polarization within the gaps arises from aligned dust grains, possibly due to their unique distribution or properties.
The study leaves questions about the exact mechanisms behind the alignment of dust grains unanswered. While it is unclear whether the alignment follows the magnetic field of the disk, typical for dust outside protoplanetary disks, the data indicate a mechanical alignment—potentially influenced by the aerodynamics of the revolving dust grains around the young star.
ALMA’s exceptional capabilities as the world’s most powerful millimeter/submillimeter telescope position it as a fundamental instrument for ongoing research into the intricate details of planetary system formation. As ALMA continues to push the boundaries of observational precision, the mysteries within the dusty realms of young stars like HL Tauri are poised to unfold further.