Star and Planet Formation and Evolution, and the Search for Life

Figure-1-1-3-1.pngMost models of planet formation entail growth from accretion from small pebbles to rocks to planetesimals in a dusty disk. But the possibility exists for planets to form from large collapsing clouds in a disk with spiral arms, if the disk is more than 10% the stellar mass and gravitationally unstable to non-Keplerian dynamics. ALMA observations of the CO emission from the disk around the Class II protostar and disk, AB Aurigae (2.4 M⊙ and 3.5 Myr old), shows such an unstable spiral disk of gas and dust, with a disk to stellar mass ratio of about 1/3. This unstable gas disk suggests that there may be multiple channels toward planet formation in protoplanetary disks, including direct collapse of a massive gas fragment.

Left: ALMA and VLT images of the gas and dust in the protoplanetary disk around AB Aurigea, showing dynamical evidence for a massive disk and spiral structure that may enhance monolithinc massive planet formation (Speedie et al. 2024 Nature 633, 58).  The CO column density, mean velocity, and velocity dispersion are shown.

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Complex molecular chemistry, including large organic molecules, has become a key field in astronomy, on the path toward understanding the development of life in the Universe. One challenge for such studies is accurate knowledge of rest frame frequencies of transitions from these molecules. The GBT has been used, in concert with high resolution (2 kHz) laboratory measurements, to obtain an accurate spectrum of propynal (HCCCHO) emission from the well-studied molecular cloud, TMC-1. These measurements also provide a greatly improved knowledge of the rest frequencies of the complex spectrum of propynal. The new data imply a propynal column density of 7x1012 cm-2, five times higher than previous studies, with a surprisingly low excitation temperature of 3 K. The results highlight the synergy between laboratory and astronomical chemistry, and emphasize that accurate spectral catalogs are essential to the success of modern astronomical facilities, and will only become more important as the next generation of facilities come online.

Right: GBT spectra of propynal (HCCCHO) emission transitions from TMC-1 (black trace), plus model fitting based on new laboratory measurements combined with the GBT spectra (Remijian et al. 2024 arXiv:2409.16435).

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The Protostellar Outflows at the EarliesT Stages (POETS) large program at the VLBA is designed to understand the enigmatic mechanisms behind jet launching from forming massive stars via measurements of water maser proper motions in a sample of 37 young stellar objects. A detailed study of the YSO 21078+5211 shows a maser 3D velocity field consistent with a magnetohydrodynamic (MHD) model of a wind created in an accretion disk associated with the forming star, with the jet launch radius of about 10 au. The jet both collimates and accelerates to 60 km/s out to 50 au. At 100 au distance, the masers trace a slower shock front possibly driven by magnetic pressure.

Left: Water maser 3D velocities in IRAS 21078+5211 from the VLBA. Right: 3D model of the MHD disk-wind in this source, with maser spots overlaid on MHD streamlines predicted by simulations of a jet around a forming massive star (Moscadelli et al. 2024 arXiv:2408.11968).

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The VLA, ALMA, and the JWST have teamed-up for an in-depth study of star formation in the luminous infrared Seyfert galaxy NGC 7469, at a resolution of ~100 pc, in particular in the starburst ring that dominates star formation in this AGN host galaxy. Observations include 1.2 mm dust continuum, CO2-1 line, VLA 22 GHz continuum, and starlight and polycyclic aromatic hydrocarbon (PAH) emission with the JWST. A star formation rate of 11.5 M⊙/yr and molecular gas mass of 6.4x109 M⊙ are derived. The star formation distribution along the ring is traced closely by the 22 GHz, 1.3 mm, and 7.7 µm PAH emission. The gas mass to star formation rate relationship in NGC 7469 is found to be intermediate between starburst galaxies and galaxies hosting an active nucleus.

Right: VLA 22 GHz continuum (color and white contours) plus ALMA 1.3mm continuum contours (black) of the IR-luminous Seyfert galaxy NGC 7469. Right: JWST F770W image, with same black ALMA contours  (Zanchettin et al. 2024, arXiv:2406.07901).

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