Combined VLA/ALMA view of the forming planetary system HL Tauri

vlashowsearl

Image: Combined ALMA (red) and VLA image of HL Tau. Credit: Carrasco-Gonzalez, et al.; Bill Saxton, NRAO/AUI/NSF. The paper is Carrasco-Gonzalez et al., “The VLA view of the HL Tau Disk – Disk Mass, Grain Evolution, and Early Planet Formation,” accepted by Astrophysical Journal Letters (preprint). The image above is certainly ground-breaking, and has been noted extensively elsewhere. The age of the system is thought to be less than 100,000 (105) years and HL Tau itself is quite Sun-like, spectral type K5. It was already known to host a protoplanet (the bright clump in the yellow VLA data above) about 14 times as massive as Jupiter and about twice as far from HL Tau as Neptune is from our Sun. From the abstract:

The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk-planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surface density profiles and grain size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. We obtain a total disk dust mass of 0.001 – 0.003 Msun, depending on the assumed opacity and disk temperature. Our optically thin data also indicate fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright rings.

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