There's something strange going on inside the protoplanetary disk of a nearby star and astronomers are at a loss to explain what it means.
AU Microscopii (AU Mic) is a young star sporting one of the finest examples of an edge-on dusty circumstellar disk. Planetary formation models predict that this disk will one day give rise to a system of planets, but there's something stirring inside the disk that no planetary formation model can currently account for.
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After astronomers analyzed observational data from the European Southern Observatory's SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) instrument, which is attached to the Very Large Telescope (VLT) in Chile, they saw what appeared to be very fast-moving wave-like structures traveling away from the star through the disk.
Located only 32 light-years from Earth allows us a very detailed view of this disk, and after looking back over archived Hubble Space Telescope data, the features were detected after some image analysis.
Anthony Boccaletti, of the Paris Observatory and lead author of a paper published in the journal Nature, explains that the structures have "an arc-like, or wave-like structure, unlike anything that has ever been observed before."
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Now, it is well known that circumstellar disks, particularly disks surrounding young stars like AU Mic, are highly dynamic places, but the speed at which these objects are moving doesn't seem to match any known planet formation phenomenon. After clocking the distance traveled between 2011 to 2015, the researchers calculated these things are moving at a velocity of 10 kilometers per second (22,000 miles per hour).
At these speeds, the objects are likely going to escape the gravitational pull of the star, a factor that discounts some possible formation mechanisms. These mechanisms include collisions between large asteroids in the disk and gravitational perturbations by small, young planets.
Although this is a mystery for now, the researchers' best guess is the driving mechanism behind these wave-like structures originates from the star itself and not from within the thick circumstellar material. A fascinating possibility being considered is that the wave-like pattern is the result of a pretty savage space weather event.
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"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 Glenn Schneider, of Steward Observatory in Tucson, Ariz., in a statement. "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."
This hypothesis is far from being proven, however. Other flaring stars with well-formed circumstellar disks have been observed before and yet AU Mic is the first example that exhibits this behavior. It could be that the mystery is far from being solved and astronomers may need to adjust their models to account for violent flows of matter during the formation of planets. Or it could be evidence of one very unlucky exoplanet being savaged by its host star.
Source: Hubblesite.org, h/t Lance Thomas