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Astronomers Spot Whirlwind Crescent Of Dust Where A Planet May Be Forming

Schematic view of the vortex surrounding a potential planet-in-the-making around the star HD 163296. Image Credit: J. Varga et al.
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Astronomers have detected a peculiar whirlwind of pebbles, dust, and gas surrounding a young star. They suspect it could be an exoplanet forming within the crescent of material.

Published in Astronomy & Astrophysics, the discovery is around a star already known for having fledgling exoplanets. In 2019, researchers found that this system was forming three exoplanets on wide orbits. In particular, they were able to detect evidence of the enormous vertical flow of gas in the disk of material from which the planets were forming. They pictured it as an enormous waterfall powered by the planet formation.

The potential new planet around HD 163296 – a star located 330 light-years away from us in the constellation Sagittarius – is actually much closer to the star than the three other planets. This new disk feature is roughly the same distance from its star as Mercury is from the Sun, but is moving more quickly than Mercury, with the hottest part of the disk rotating about once a month.

It's this temperature that attracted the team to investigate the whirlwind. Compared to the rest of the disk, this region appeared much hotter. The team suspected that the hot spot was indeed a vortex, where dust was the dominant component.

Simulations supported this idea. Computer models suggest that collisions in the vortex would grind pebbles down so that only dust would remain, unlike the rest of the disk where dust and pebbles clump together. This finding is important in understanding how planets might form. In particular, it could be an indication of how rocky terrestrial planets like ours come to be.

ALMA image of the protoplanetary disk surrounding the young star HD 163296, the new observations zoomed right into the middle. Image Credit: ALMA (ESO/NAOJ/NRAO); A. Isella; B. Saxton (NRAO/AUI/NSF) CC BY 4.0

The observations were possible thanks to a very clever trick. By combining infrared observations from four of the telescopes of the ESO Observatory's Very Large Telescope on Cerro Paranal, a mountain in the Atacama Desert, Chile, the team was able to create a “virtual telescope” with a diameter of 200 meters (660 feet), much bigger than each individual telescope in the observatory. This is certainly a case of the whole being greater than the sum of its parts, as long as you know how to put those parts together.

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The gas disk surrounding the star is among the brightest seen so far, which made the observations possible over the last few years. The team hopes to apply this approach to other systems, expanding our understanding of planetary formation.  

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