An article just published in the journal “Nature” describes the discovery of mysterious ripples across the disk of dust surrounding the star AU Microscopii, or AU Mic. Through SPHERE, an instrument mounted on ESO’s Very Large Telescope, a team led by Anthony Boccaletti, LESIA (Observatoire de Paris/CNRS/UPMC/Paris-Diderot), France, discovered these structures never seen before and yet to be explained.
AU Microscopii is a very young star since its age is estimated at around 12 million years. Its distance is about 32 light years from Earth and is invisible to the naked eye because it’s a red dwarf that has a brightness much lower than that of the Sun. Its name is due to the fact that it’s located in the constellation Microscopium.
The dust disk around AU Microscopii was discovered in 2003 and has since been the subject of several observations, also with the Hubble Space Telescope, looking for planets, also in formation. Recently, it’s been possible to study this star and its dust disc with SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch), an instrument that entered its test phase a little over a year ago.
The main purpose of SPHERE is to study exoplanets thanks to the possibility of seeing them directly. In the case of AU Microscopii, instead of finding planets, the astronomers were surprised to discover strange structures like no one had ever seen before.
After this discovery, the astronomers went to search the archive of images captured by the Hubble Space Telescope finding those structures in observations made in 2010 and 2011. At the time, the ripples weren’t recognized because no one realized that there could be such an anomaly but this time the astronomers knew what to look for. In fact, they found the structures already seen with SPHERE and they realized that they changed over time.
These ripples change rapidly over time and those distant from the star appear to move faster than those close to it, up to 40,000 km/h (about 22,000 mph). The astronomers found at least three structures that move so quickly that they could well escape the gravitational attraction of the star.
For now there are only hypotheses about these ripples. According to Glenn Schneider of Steward Observatory, USA, co-author of the research, they could be linked to the star’s flares. A flare could have triggered some reaction in a possible planet ripping material violently from it. That material may have propagated through the disc because of the flare’s strength.
More observations will be needed to see if there are planets in the AU Microscopii system and in that case if the hypothesis about the ripples origin makes sense. SPHERE has proved very useful in the study of a dust disk but other instruments can help this research such as the ALMA radio telescope.
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