49 China, from which we are separated by some 189 light years away, would be the most common star, if not the environment. It would seem, and spectral A1VC class is not as rare as the blue giants (though not as frequent as red dwarfs), and metallicity the most that neither is common, and mass (2,17 sun) is not extraordinary. But there is an important detail: around it at a distance and fifty. that is a lot of gas, this cloud.

Meanwhile, the star, according to different estimates, from 40 to 60 million years. Usually the gas cloud as the formation of planetary systems naturally resolved. That is, after the first million years of life excess gas around a star just can't be (unless it's from a region with a high concentration of interstellar gas). But 49 China for 17 years (in spite of the puzzled astronomers?) demonstrates what should not be. So where does gas there?

Benjamin Zuckerman from the University of California in Los Angeles and Inseok song from the University of Georgia (both - USA) suggested the following. It's all in excessive, exaggerated version of the Kuiper belt, present in this young system. The mass of our zone is 0.1 earth. The last 4.5 billion years pretty thinned it: many comets falling, and falling on the planet. In the beginning, after the formation of the Solar system, it weighed 40 earth masses and is successfully implemented intense bombardment and Earth and other celestial phone

According to the calculations of astronomers, "Kuiper belt" 49 whale weighs 400 earth masses, that is ten times heavier than the young Sun, and 4 thousand times than now.

The conditions are extreme. "Hundreds of trillions of comets revolve around 49 China and another star that little younger, about 40 million years. Imagine this Prorva, each comet the size of the campus of the University of California (about 1.6 km in diameter), it all revolves around a star, and now and then stumbles upon each other, - draws large strokes Mr. Zuckerman. - According to our calculations, comets around both stars [with powerful analogues of the Kuiper belt] face every six seconds. I was astonished when we got these numbers". Moreover, the situation lasts for 10 million years. Something similar around other stars? Astronomers were able to find only one example. Tellingly, it was also white young star of spectral class a - HD 21997.

In our system, collisions between comets extremely rare, for they comets are small. Usually, "our" comet collide with planets or other large bodies. But where hundreds of trillions, everything is turned on its head, no matter how small comets, there are too many, so you can avoid a dozen mutual shocks per minute.

Still not clear what implications this may have for the development of the whole system. More or less accurately you can evaluate only the amount of gas released after these collisions. Again, a little closer to the star, especially inside her "snow line", the comet should encounter less that can prevent the formation of planets there, although the instruments and do not discover them. But you can say that the formation of giant planets in the area where the comet belt of such weight, should radically differ from the well-known scenarios.

Report on the study published in the Astrophysical Journal, and its Preprint available here.

Based on the materials of the University of California in Los Angeles.