Unexplained ripples streaking away from neighboring star could hold clues to planet formation

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The scientists say that the objects are moving too quickly to resemble conventional disc features that might be pulled away by nearby objects, such as planets orbiting the star(Credit: ESO, NASA & ESA)

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Astronomers have been left puzzled after images from the ESO's Very Large Telescope in Chile revealed mysterious wave-shaped structures around a nearby star, the likes of which have never been seen before. The features were observed in the disc of dust surrounding the young star AU Microscopii (AU Mic), and could lead to a new understanding of how planets form inside such discs.

At around 12 million years old, AU Mic is a very young star located only 32.3 light years away from Earth. Astronomers have combed the discs of space debris that circle stars, such as AU Mic, in hope of uncovering hints as to how they bring about the formation of planets. Last year, a team of astronomers pointed SPHERE, an exoplanet hunting imaging instrument on the Very Large Telescope, at AU Mic for this very purpose, yielding some very surprising results.

"Our observations have shown something unexpected," says Anthony Boccaletti of Observatoire de Paris, France. "The images from SPHERE show a set of unexplained features in the disc which have an arch-like, or wave-like, structure, unlike anything that has ever been observed before."

The team liken the features to water ripples, observing five wave-like arches each at varying distances to the star. Looking to consolidate its findings, the team dug up previous images of AU Mic's disc taken by the Hubble Space Telescope in 2010 and 2011, which added even further to the mystery.

"We reprocessed images from the Hubble data and ended up with enough information to track the movement of these strange features over a four-year period," explains member of the research team Christian Thalmann, from ETH Zürich, Switzerland. "By doing this, we found that the arches are racing away from the star at speeds of up to about 40, 000 km/h (25,000 mph)!"

The scientists say that the objects are moving too quickly to resemble conventional disc features that might be pulled away by nearby objects, such as planets orbiting the star. They say that the outer waves are moving much faster than the inner ones, and at least three of the features are moving at such a rate they could well escape the star's gravitational pull.

So what does it all mean exactly? The scientists are not yet sure, but they do have a few ideas.

"One explanation for the strange structure links them to the star’s flares," says Glenn Schneider of Steward Observatory, a member of the research team. "AU Mic is a star with high flaring activity — it often lets off huge and sudden bursts of energy from on or near its surface. One of these flares could perhaps have triggered something on one of the planets — if there are planets — like a violent stripping of material which could now be propagating through the disc, propelled by the flare’s force."

If nothing else, the researchers are pleased that SPHERE is already proving valuable so quickly, having only been installed on the Very Large Telescope midway through last year. They plan to continue observing the AU Mic system in hope of unraveling the mystery.

The research was published in the journal Nature.

Source: ESA

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