Planet creates dust trap 

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Do you recognize this image? If you are a regular visitor of the ALMA website, you may have seen similar photos before. Yes, this is a protoplanetary disk – a flat, rotating disk of gas and dust around a newborn star. In the future, particles in the disk will clump together to form new planets. 

The star itself cannot be seen in the ALMA images. That’s because it is young and hot. It hardly emits any radiation at millimeter and submillimeter wavelengths – the type of radiation that ALMA is sensitive to. The disk, however, has a much lower temperature. It glows at submillimeter wavelengths. 

The disk consists of two parts: a bright inner ring and a fainter outer ring. The dark gap between the two rings contains much less dust. That’s probably because a planet is already orbiting there. The planet sweeps up the dust and creates an empty zone. 

But if you look closely, you’ll see that the outer ring is uneven. On the top of the image, it’s much brighter than on the bottom. Apparently, there’s more dust there. 

This region is called a ‘dust trap’. Dust particles are trapped by the gravitational influence of the planet in the empty zone. The particles stay close to each other. Eventually, they may clump together to form yet another planet. 

Astronomers already suspected that dust traps must exist in protoplanetary disks. Without them, dust particles would slowly spiral into the central star. No planets would ever form. But this ALMA image is the first one that clearly shows the dust trap. 

The star at the center of the disk is called V1247 Orionis. It lies about a thousand light-years away, in the constellation Orion. The ALMA observations of the disk were carried out by a large international team of astronomers, led by Stefan Kraus of the University of Exeter in the United Kingdom. The new observations have been published in The Astrophysical Journal Letters.

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