Mysterious Ripples Found Racing Through AU Mic's Disk

Posted on October 7, 2015

Astronomers have found mysterious wave-like ripples racing through the planet-forming circumstellar disk of star AU Microscopii (AU Mic). The features were discovered using NASA's Hubble Space Telescope and the European Southern Observatory's (ESO) Very Large Telescope in Chile. The astronomers say nothing like it has been observed before - or even predicted - in a circumstellar disk.

AU Mic is located 32 light-years away in the southern constellation Microscopium. The star's circumstellar disk is tilted edge-on to our view from Earth making it an optimal star for astronomers to observe. The image above shows the ripple observations and the image below is the debris disk of AU Mic. The wave-like ripples were discovered using ESO's SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) instrument.

Anthony Boccaletti, the study's lead author from the Paris Observatory, says in a statement, "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."

The astronomers also looked back at earlier Hubble images of the disk from 2010 and 2011 and were able to find the ripples that had not been noticed at the time the images were taken. The astronomers also observed that the ripples are moving very fast at speeds up to 22,000 miles per hour (10 kilometers per second).

Team member Christian Thalmann of the Swiss Federal Institute of Technology in Zurich, Switzerland, says, "We ended up with enough information to track the movement of these strange features over a four-year period. 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)!"

The astronomers have ruled out the possibility that the features are caused by the gravitational attraction of the star itself or of nearby objects. They have also ruled out comet or asteroid collisions. One theory that has not been ruled out is high energy flares coming from AU Mic.

A research paper on the fast-moving features in AU Mic's debris disk can be found here in the journal Nature. All the released images can be found here on HubbleSite.



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