An international team of astronomers has announced a baffling discovery never seen before: an extraordinary amount of dust around a nearby star mysteriously disappeared.
An artist's conceptualization of the dusty TYC 8241 2652 system as it may have appeared several years ago, when it was emitting large amounts of excess infrared radiation, left, and as it might appear now after most of the surrounding dust has disappeared (Gemini Observatory/AURA artwork by Lynette Cook)
This cosmic vanishing act occurred around a star some 450 light years from Earth, in the direction of the constellation Centaurus.
“It’s like the classic magician’s trick — now you see it, now you don’t,” said Dr Carl Melis, a postdoctoral scholar at the University of California in San Diego and lead author of a paper describing the discovery in the journal Nature. “Only in this case, we’re talking about enough dust to fill an inner solar system, and it really is gone!”
“It’s as if the rings around Saturn had disappeared,” said co-author Prof Benjamin Zuckerman of the University of California in Los Angeles. “This is even more shocking because the dusty disc of rocky debris was bigger and much more massive than Saturn’s rings. The disc around this star, if it were in our Solar system, would have extended from the Sun halfway out to Earth, near the orbit of Mercury.”
“A perplexing thing about this discovery is that we don’t have a satisfactory explanation to address what happened around this star,” Dr Melis said. “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.”
Dr Melis describes the star, called TYC 8241 2652, as a “young analog of our Sun” that only a few years ago displayed all of the characteristics of “hosting a solar system in the making,” before transforming completely. Now, very little of the warm, dusty material thought to originate from collisions of rocky planets is apparent.
“Nothing like this has ever been seen in the many hundreds of stars that astronomers have studied for dust rings,” Prof Zuckerman said. “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 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 emission 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 warm dust has now been gone for two-and-a-half years.
“Because so much dust had been orbiting around the star, planets very likely are forming there,” Prof Zuckerman said.
“Although we’ve identified a couple of mechanisms that are potentially viable, none are really compelling,” Dr 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 disc, which then instigate a runaway process where small grains chip into oblivion both themselves and also larger grains.”
Major dusty regions are known to exist in our own Solar system and include the asteroid belt between the orbits of Mars and Jupiter and another located beyond the orbit of Neptune. Nearly 30 years ago, NASA’s Infrared Astronomical Satellite (IRAS) first discovered many similar regions orbiting other stars — but no disappearing act like the one at TYC 8241 2652 has ever been seen during these three decades.
“We were lucky to catch this disappearing act,” Prof Zuckerman said. “Such events could be relatively common, without our knowing it.”
_______
Bibliographic information: Melis C et al. 2012. Rapid disappearance of a warm, dusty circumstellar disk. Nature 487, 74–76 (05 July 2012); doi: 10.1038/nature11210
