Winding up for planet formation

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By ScienceAdviser. 

Excerpt: Understanding how planets form in the disks of dust and gas around newborn planets is a work in progress. Only recently have astronomers spied planets carving out rings in the disks by scooping up material. But some disks have a spiral structure. Is that the result of gravitational interactions in the disk itself, before planets form, or are newborn planets themselves warping the disk into a spiral? A team of astronomers say they’ve resolved this chicken-and-egg puzzle using the Atacama Large Millimeter/submillimeter Array (ALMA), a collection of 66 dish antennas high up in the Chilean Andes which can see dust in disks but not the planets themselves. If the spiral arms formed in the disk spontaneously, over time they would wind tighter, like the spring in a wind-up clock. Arms formed by planets would keep their shape as they move around the nascent star. The team used archival and new images taken over 7 years of the young star IM Lup to make a stop-motion video of the spiral disk around it. The video shows the spiral winding tighter as it turns which, the team says in Nature Astronomy on 24 September, shows it is a disk on the cusp of forming planets.... 

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