AU Microscopii, AU Mic in short, is a star in the Southern hemisphere at a distance of about 10 parsec i.e. 33 light years. This is a young system about twenty million years old, which still contains large quantities of dust.
This dust constitutes a ring shaped disc referred to as a debris disc, since the dust grains are produced by the constant collisions of large asteroid type bodies, or are left behind by comets. This is probably a newly created planetary system in which planets could already have been formed.
The disc of AU Mic is such that it can be seen edge on, and it extends to over 200 astronomical units (1 u.a. = Earth-Sun distance).
The first observations made by the SPHERE instrument in 2014 showed the presence of large dusty structures with wave like ondulations “above” the equatorial plane of the disc. A comparison with earlier data from the Hubble space telescope shows that these structures were already present in 2010 and that they have moved during the period 2010 to 2014, certain of them at very high speeds (about 10 km/s), which is higher than the escape speed.
As a consequence, this dust is likely to have been ejected from the system and freed from the gravitational attraction of the star.
AU Mic is in fact less massive than the Sun, but is much more active.
Observations published on Friday June 15 2018 in the journal Astronomy & Astrophysics show that the motion of the structures continued from 2014 to 2017 at speeds of several km/s and that new structures were born. Furthermore, the analysis of earlier data has shown that these structures were already present as early as 2004.
Two hypotheses involving stellar activity could explain this surprising phenomenon :
- either the production of the dust in these structures is limited to the system and is located at a definite point with respect to the observer ; this could then be the result of an earlier collision, corresponding to the disintegration of an asteroid or a dwarf planet.
- or it could come from a body rotating around the star. In this latter case, a planet could eject this dust directly via an as yet unknown mechanism.
In order to find an answer to these questions and to understand the formation of dusty structures in the AU Mic system, it is essential to continue the observations with the SPHERE instrument and the HST as well as with the upcoming telescopes such as the JWST.
To know more :
https://www.obspm.fr/decouverte-de-mysterieuses.html?lang=en