Astronomers have never seen anything like it, and neither did they expect to.
A team of researchers spotted the phenomenon while analyzing the dust and debris surrounding the star AU Microscopii, or AU Mic, using the Very Large Telescope’s SPHERE instrument. AU Mic is a relatively young star. By watching its protoplanetary disc, astronomers hope to gain a better understanding of how planets form and evolve.
But now, thanks to the high-contrasting imaging abilities of SPHERE, scientists have a new mystery.
“Our observations have shown something unexpected,” Anthony Boccaletti, an astronomer at the Observatoire de Paris, France, said in a press release. “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.”
Boccaletti is the lead author of a new paper on the phenomenon, published this week in the journal Nature.
Analysis shows the ripples are moving quite fast, and that portions of the wave-like feature are moving faster as they get farther away from star — fast enough to escape the gravitational pull of AU Mic. Scientists say the ripple’s speed suggests an external force is at play.
“Everything about this find was pretty surprising!” said co-author Carol Grady, a researcher with Eureka Scientific, in the United States. “And because nothing like this has been observed or predicted in theory we can only hypothesise when it comes to what we are seeing and how it came about.”
Researchers have ruled out asteroids and gravitational instability as possible causes of the ripple, but they still don’t know what might be responsible for the wave-like movements.
Currently, their most promising guess is that a stellar flare set of a chain reaction — a ripple effect.
“One explanation for the strange structure links them to the star’s flares. 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,” explained co-author Glenn Schneider, as astronomer at Steward Observatory, at the University of Arizona. “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.”