THE UNIVERSE - ENIGMATIC STAR

Enigmatic disappearance around a star

Is there any magician around the TYC 8241 2652 1 star? This very young star, similar to our Sun and located at 456 light years from us, just disappear, as if by magic, almost the entirety of the huge disk of dust which surrounded it. "It is like the Tower of magic classic: move is, a blow there is more", summarizes Carl Melis, astronomer at the University of California (San Diego), and main author of the article published in Nature on 5 July, where this enigmatic disappearance is described first. Except that this time, it's not a rabbit that can slip into the bottom of a high hat of shape: "in this case, we are talking about a quantity of sufficient dust to fill an inner solar system (in the case of our system solar, it's space including the orbits of mercury, Venus, Earth, Mars and the asteroid belt)"(,_NDLR), and it is really a party ", adds Carl Melis.

TYC 8241 2652 1 is a star of about 10 million years. Next to our Sun and its almost 4.6 billion years, it is a young child. But this is not really a baby who is born. In its short existence - scale astronomical - residues of its formation (gas, ice, dust) have had the time to try agglomerate in planet (s). It is not known if this process has resulted because no companion has for the moment been detected around this star not really close, but astronomers believe that the dust disk that a few years ago, surrounded TYC 8241 2652 1 was not the original disk from which to manufacture the planets but rather a secondary diskconsisting of grain from the multiple collisions that embryos of planets (planetesimals) had suffered. Heated by the Sun, these dust fishnets in infra-red and it is in this wavelength that they had been detected as early as 1983.

That have thus been exactly astronomers?They followed the evolution in time of infra-red radiation of this drive by recovering data from four space telescopes working in this field - IRAS in 1983, Akari in 2006, WISE in 2010 and Herschel in 2011-, that they were supplemented by observations on the ground made with the telescope at Gemini South in the Chile (in 2008, 2009, 2012) and the NASA Infrared Telescope Facility of Hawaii (2011). Until 2008, the amount of light emitted by the disk is stable. When new measures are carried out in 2009, it fell close to a third party. And in 2010, this figure has again been divided by ten and what is left of the disk is at the limit of detectable. "It is as if the rings of Saturn were missing, said one of the authors of the Naturearticle, Benjamin Zuckerman, Professor in the Department of physics and Astronomy of the University of California (Los Angeles)." " Is even more surprising because this dusty debris disk was larger and much more massive than Saturn's rings."

The problem of the researchers, is that no known model is able to do away with such a quantity of matter within two years. "Nothing similar has never been observed around hundreds of stars that astronomers have studied the disks of dust, adds Benjamin Zuckerman." " The disappearance of the dust around TYC 8241 2652 1 was so weird and so fast as in the beginning, I thought that strange stuff had distorted our observations."But that was not the case. In addition, during the two years in question, the star demonstrated stability and seems to have known no violent anger to sweep the dust.

For the moment, the astronomers have in hand than two assumptions a little dysfunctional to try to understand what happened. The first imagine that the presence of gas in the disk causes accretion of dust in the direction of the star. The problem is there, to succeed such cleaning in such a short time, a mass of gas 10 times superior to that of the disk of dust and that the authors of the study are well confused to explain where such a quantity of gas could come. The latter staged a violent collision between planetesimals or even the breakup of one of them. In both cases, a large amount of small debris is ejected in the disk. Under certain conditions, they would be able to cause a snowball effect, hitting grains of dust from the disk, with chips, in turn, going to hit other grains, etc. This avalanche of collisions could lead to the disintegration and the evacuation of the majority of the grain. The scenario is pretty but, also, it faces a problem of size because the model that he resumed, conceived in 2006, refers to a process for about... one thousand years, not two.

The puzzle of the TYC 8241 2652 1 star adds yet more complexity to the poorly known phenomena that are at work in these disks of dust. Phenomena that interest astronomers because they are responsible for the formation of the planets and all systems solar, more or less exotic, that researchers discovered since 15 years.