AU Microscopii
Astronomers using NASA's Hubble Space Telescope and the European
Southern Observatory's (ESO) Very Large Telescope in Chile have
discovered never-before-seen moving features within the dusty disk
surrounding the young, nearby star AU Microscopii (AU Mic). The
fast-moving, wave-like structures are unlike anything ever observed in a
circumstellar disk, said researchers of a new analysis. This new,
unexplained phenomenon may provide valuable clues about how planets
form inside these star-surrounding disks.
AU Mic is located 32 light-years away in the southern constellation
Microscopium. It is an optimal star to observe because its circumstellar
disk is tilted edge on to our view from Earth. This allows for certain
details in the disk to be better seen.
Astronomers have been searching AU Mic's disk for any signs of clumpy
or warped features that might offer evidence for planet formation.
They discovered some very unusual, apparently outward-moving features
near the star by using ESO's SPHERE (Spectro-Polarimetric High-contrast
Exoplanet Research) instrument, mounted on the Very Large Telescope.
"The images from SPHERE show a set of unexplained features in the
disk, which have an arc-like, or wave-like structure, unlike anything
that has ever been observed before," said Anthony Boccaletti of the
Paris Observatory, the paper's lead author.
The images reveal a train of wave-like arches, resembling ripples in
water. After spotting the features in the SPHERE data the team turned
to earlier Hubble images of the disk, taken in 2010 and 2011. The
wave-like nature of some of these features were not recognized in the
initial Hubble observations. But once astronomers reprocessed the Hubble
images they not only identified the features but realized that they
had changed over time. The researchers report that these ripples are
moving — and they are moving very fast.
"We ended up with enough information to track the movement of these
strange features over a 3- to 4-year period," explained team member
Christian Thalmann of the Swiss Federal Institute of Technology in
Zurich, Switzerland. "By doing this, we found that the arches are
racing away from the star at speeds of up to 10 kilometers per second
(22,000 miles per hour)!" Co-investigator Carol Grady of Eureka
Scientific in Oakland, California, added, "Because nothing like this has
been observed or predicted in theory we can only hypothesize when it
comes to what we are seeing and how it came about."
The ripples farther away from the star seem to be moving faster than
those closer to it. At least three of the features are moving so fast
that they are likely escaping from the gravitational attraction of the
star. Such high speeds rule out the possibility that these features are
caused by objects, like planets, gravitationally disturbing material
in the disk. The team has also ruled out a series of phenomena as
explanations, including the collision of two massive and rare
asteroid-like objects releasing large quantities of dust and spiral
waves triggered by instabilities in the system's gravity.
"One explanation for the strange structure links them to the star's
flares. AU Mic is a star with high flaring activity. This is typical
for such young, relatively cool, low-mass stars. AU Mic often lets off
huge and sudden bursts of energy from on or near its surface,” said
co-author and leader of the Hubble team Glenn Schneider of Steward
Observatory in Tucson, 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 disk, propelled by the flare's force."
The team plans to continue to observe the AU Mic system to try to
understand what is happening. But, for now, these curious features
remain an unsolved mystery.
The results will be published Oct. 8 in the British science journal Nature.
Contacts
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu
Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov
Mathias Jäger
ESA/Hubble, Garching, Germany
011-49-176-6239-7500
mjaeger@partner.eso.org
Anthony Boccaletti
Paris Observatory, CNRS, Paris, France
011-33-1-4507-7721
anthony.boccaletti@obspm.fr
Glenn Schneider
Steward Observatory, University of Arizona, Tucson, Arizona
520-621-5865
gschneider@as.arizona.edu
Source: HubbleSite
