6 July 2012

Astronomers ponder proto solar system vanishing act

by Will Parker

Displaying all of the characteristics of a solar system in the making, a massive cloud of dust and rocky debris orbiting a nearby star has vanished, leaving astronomers mystified as to what could have happened to the dusty disc that was much more massive than Saturn's rings.

"It's like the classic magician's trick - now you see it, now you don't," enthused University of California San Diego's Carl Melis, lead author of a paper detailing the disappearing act in Nature. "A perplexing thing about this discovery is that we don't have a satisfactory explanation to address what happened around this star," he adds. "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."

The cosmic vanishing act occurred around a star designated TYC 8241 2652, around 450 light years from Earth in the direction of the constellation Centaurus. Size-wise, if the disappeared disc were in our solar system, it would have extended from the Sun halfway out to Earth's orbit.

The dust had been present around the star since at least 1983, and it continued to glow brightly in the infrared for 25 years. In 2009, it started to dim. By 2010, the dust was gone; the astronomers observed the star twice that year from the Gemini Observatory in Chile, six months apart. An infrared image obtained by the Gemini telescope as recently as May 1 of this year confirmed that the dust has now been gone for two-and-a-half years.

"Nothing like this has ever been seen in the many hundreds of stars that astronomers have studied for dust rings," said paper co-author Benjamin Zuckerman, from the University of California - Los Angeles. "This disappearance is remarkably fast, even on a human time scale, much less an astronomical scale. The dust disappearance at TYC 8241 2652 was so bizarre and so quick, initially I figured that our observations must simply be wrong in some strange way."

The lack of an existing model for what is going on around this star is forcing astronomers to rethink what happens within young solar systems in the making. The dust likely resulted from a violent collision - but that does not explain where it went.

"We've identified a couple of mechanisms that are potentially viable," Melis offered. "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 disc, which then instigate a runaway process where small grains chip into oblivion both themselves and also larger grains."

But the authors concede that these two scenarios are probably unlikely. "None [of our scenarios] are really compelling," Melis opined.

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Source: University of California - Los Angeles