Just 29 light-years away from us, the star AU Microscopii can be described as a close neighbor. This red dwarf, which is ‘only’ half the mass of our Sun, lies in the southern constellation Microscopium — unfortunately, is not visible in the northern hemisphere. Until 2014, astronomers considered it a ‘simple’ young star surrounded by a large disc of dust (the protoplanetary disk, the cradle of planets)… but AU Microscopii is not simple, its hide something very unusual.
From data provided by ESO’s Very Large Telescope (VLT) in Chile and the Hubble Space Telescope, an international team of astronomers, led by Dr. Anthony Boccaletti of the Paris Observatory, revealed an intriguing phenomenon within the dusty disc around AU Microscopii: a fast-moving wave-like structures traveling at high speed in the protoplanetary disk — unique features unlike anything ever observed.
Our observations have shown something unexpected. 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,
said Dr. Boccaletti ~ lead author on a study published in the journal Nature.
The ‘waves’ in question, are moving away from the star at speeds ranging from 4 to 10 kilometers per second, and those located furthest from the star appear to move fastest. At least three of them go fast enough to eventually escape the gravitational attraction of AU Microscopii.
We reprocessed images from the Hubble data and 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 about 22,000 miles per hour (10 km per second),
said co-author Dr Christian Thalmann.
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,
said co-author Dr Carol Grady.
So, what cause these mysterious ripples? For now, scientists are left to speculate. After dismissing the possibility of gravitational perturbations caused by the planets, or the collision of large asteroids, they issued a theory: ‘guilty’ could be … solar flares.
One explanation for the strange structure links them to the star’s flares,
said co-author Dr Glenn Schneider.
AU Microscopii is a star with high flaring activity – it often lets off huge and sudden bursts of energy from on or near its surface.
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,
Young stars, like AU Microscopii, are wildly active. They emits large amounts of energy and matter in space — as huge eruptions of charged particles. If one of these eruptions, common on AU Microscopii, hits a forming planet, it could easily strip material away from the planet and propagate it outward at rapid speeds.
For now, no planet has been observed. Researchers continue, of course, to study the star and its disk of debries to understand what is happening.
We wish we knew what it was,
says co-author John Debes.
But sometimes you just have to throw up you hands and say ‘We don’t know what it is yet and we’ll keep looking and keep thinking to try to come up with the answer.
© Featured image credit: Top and middle rows show Hubble images of the AU Microscopii disc from 2010 and 2011, the bottom row is an image taken with VLT’s SPHERE instrument in 2014. The black central circles show where the brilliant light of the central star has been blocked off to reveal the much fainter disc, and the position of the star is indicated schematically. The scale bar at the top of the picture indicates the diameter of the orbit of the planet Neptune in the Solar System (60 AU). Image credit: ESO / NASA / ESA.