An artist's conception of the now-vanished dust disc surrounding… (Gemini Observatory/AURA…)
A disc of planet-forming dust around a distant star has disappeared unexpectedly, leaving astronomers scratching their heads and questioning current theories of how planets are formed. "It's like the classic magician's trick: Now you see it, now you don't," said astronomer Carl Melis of UC San Diego, who led the team that discovered the phenomenon. "Only in this case, we're talking about enough dust to fill an inner solar system and it is really gone." The team has proposed several possible explanations for the disappearance, but "none are really compelling," Melis said.
The star in question is a called TYC 8241 2652. It is a younger version of our own sun, only about 10 million years old (our own solar system is 4.5 billion years old), and lies 450 million light-years away in the constellation Centaurus. It was first seen in 1983 by NASA's Infrared Astronomical Satellite (IRAS). The dust disc heats up from absorbed light from its star and re-emits the energy in the infrared, giving the system a characteristic appearance. IRAS has discovered hundreds of such stars.
The team reported Thursday in the journal Nature that they reexamined the star in 2008 using the Gemini South Observatory in Chile and found the same infrared signature observed in 1983. But when they looked at it again in 2009 with NASA's orbiting Wide-field Infrared Survey Explorer, about two-thirds of the dust had disappeared. Observations with other telescopes the following year showed that virtually all of the dust was gone. "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," said co-author Ben Zuckerman of UCLA.
Researchers have offered at least three potential mechanisms for the disappearance. One might be runaway planetary accretion. It is generally believed that the condensation of such dust particle around a star into a planet occurs over long periods -- hundreds of thousands of years. In this case, it could have been accelerated by some unknown force, occurring over just a few years. The star is too far away to observe any potential planet, however.
A second possibility is that, for some reason, the dust has all fallen into the star itself, perhaps as a result of the star's gravity or some external force. The third explanation might be that the dust particles are so small that the constant stream of light from the star has ejected them all into space, where they have cooled off.
"Many astronomers feel uncomfortable with the suggested explanations for the disappearance of the dust because each of them has nontraditional implications," said co-author Inseok Song of the University of Georgia. "But my hope is that this line of research can bring us closer to a true understanding of how planets form."