Planet-Forming Dust Abruptly Disappears Around Star
July 5, 2012

Planet-Forming Dust Abruptly Disappears Around Star

Lee Rannals for - Your Universe Online

One star pinpointed as a prime location for a planet-forming disk decided enough was enough, and closed-up shop suddenly.

While observing TYC 824126521, a young star located about 456 light years from Earth, researchers discovered that the planet-forming dust that once surrounded the star abruptly disappeared.

Between 2008, when the star was being observed by a powerful infrared telescope in Chile, and 2010, when NASA's WISE infrared space telescope was staring at the same star, dust that was once glowing brightly had disappeared.

"It's like the classic magician's trick: now you see it, now you don't," Carl Melis of the University of California, San Diego, who led the team, said in a prepared statement. "Only in this case we're talking about enough dust to fill an inner solar system and it really is gone!"

The dust was first seen by NASA's Infrared Astronomical Satellite back in 1983, and it remained brightly glowing for 25 years.

"A perplexing thing about this discovery is that we don't have a really satisfactory explanation to address what happened around this star. The disappearing act appears to be independent of the star itself, as there is no evidence to suggest that the star zapped the dust with some sort of mega-flare or any other violent event," Melis said.

Co-author of the paper published in the journal Nature, Ben Zuckerman, said it´s like looking at Saturn two years later, and finding its rings are no longer visible.

He said the team's observation was so bizarre, that he assumed they had just simply made an error of some sort.

One theory of what happened is that friction with intervening gas caused the dust to slow and fall onto the star.  Another idea is that the dust grains continued to crash into each other until they got blasted out of the solar system.

"The disappearance ... in less than two years is incredibly fast by our current understanding, and the impact of this is difficult to predict," astronomer Margaret Moerchen, with the European Southern Observatory (ESO) in Chile, wrote in an analysis of the research published in Nature.

It is believed the dust results from planetary system formation, and is due to collisions and reprocessing of objects like comets and asteroids. However, the disappearing dust disk is something new to astronomers.

"Although we've identified a couple of mechanisms that are potentially viable, none are really compelling," Melis said. "In one case, gas produced in the impact that released the dust helps to quickly drag the dust particles into the star and thus to their doom.

"In another possibility, collisions of large rocks left over from an original major impact provide a fresh infusion of dust particles into the disk which then instigate a runaway process where small grains chip into oblivion both themselves and also larger grains."

Image 2 (below): Artist's conceptualization of the TYC 8241 2652 system as it might appear now after most of the surrounding dust has disappeared -- based on observations by the Gemini Observatory and other ground and space-based observatories. Credit: Gemini Observatory/AURA artwork by Lynette Cook.

Image 3 (below): A hypothetical view of Saturn (with its moon Titan) with and without rings illustrating co-PI Ben Zuckerman's statement about an imaginary analogue to the TYC 8241 2652 system: "It's as if you took a conventional picture of the planet Saturn today and then came back two years later and found that its rings had disappeared." Gemini image obtained using the Near-Infrared Imager (NIRI) on Gemini North with the Altair adaptive optics system. Image alteration by Joy Pollard/Gemini Observatory/AURA.