Mystery Feature Surrounds Star: It's a (Dust) Trap!

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Dust. It’s insignificant to us, or at most, a nuisance. Dust is that little bit of nothing in our daily lives. Dust collects on things that are old or forgotten. Dust has a bad name on Earth, while elsewhere in the Universe, it turns out to be a key ingredient of the life cycles of stars and planets.

The proliferation of exoplanet discoveries over the last two decades has also been accompanied by a greater understanding of how planets form around stars. Truly,  planets come from star dust, or the left over material from the gravitational collapse of a gas cloud into a hot, nuclear powered furnace. The actual details of how this occurs, however, is still literally shrouded in mystery.

PHOTOS: ALMA: New Jewel of the Atacama Desert

One often needs a radio or infrared telescope to peer through the dark, dusty regions around forming stars and planetary systems. Sometimes, these instruments can be used to view the dust itself, which holds valuable information about the physics involved.

Above is a new image from that famous new telescope in the Chilean desert, the Atacama Large Millimeter/Submillimeter Array, or ALMA. While still in its commissioning phases, it was used to resolved a “cashew-shaped” feature of dust around the star Oph IRS 48, 390 light-years away from Earth.

The lead author of the paper is Nienke van der Marel, a Ph.D. student at Leiden Observatory in the Netherlands. He expressed initial skepticism at the strange feature, but the sharpness and sensitivity of ALMA, even without its full complement of antennas, made it clear that the “dust trap” was real.

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Such a trap, or vortex or bump, of material has been theorized as a way of solving the problems of how tiny dust grains clump together for form larger dust grains, and eventually larger and larger structures to form planets. Somehow, over just a few short million years, these need to go from dust to pebbles to boulders to worlds without self-destructing first. The action of a large gas giant in the system could create such a dust trap by gravitational interactions, thus allowing a safe space for the clumps to form. Previous observations of the forming planetary system show a gap in the disk of gas and dust, indicative of a large planet that has already begun to clear out its orbit.

The cartoon model (pictured here) of Oph IRS 48 gives a clear picture of the current working model. The blue of the disk represents the gas seen in observations of the carbon monoxide molecule. The brown indicates everything from small dust grains to larger pebbles, shown to be larger within the dust trap. These are “herded” together in a sense by the young, still-forming planet believed to be in the disk’s gap.

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ALMA is especially well suited for studying the origins of things in the Universe: planets, stars, and galaxies. High in the Atacama Desert in the Chilean Andes, it sits above much of the water vapor in the atmosphere, providing a clear view through a certain window in the electromagnetic spectrum that allows such scientific questions to be answered. Where did we come from? A simple dust trap may be a part of that answer.

Images: Top - ALMA image of the dust trap around Oph IRS 48. Credit – ALMA (ESO/NAOJ/NRAO) / Nienke van der Marel. Bottom – Artist’s impression of the proposed disk structure of Oph IRS 48. Credit – Nienke van der Marel

Of course, I can’t take credit for the Star Wars reference in the title… the good people at the National Radio Astronomy Observatory beat me to it!