The unusual thin rings of comets and dust that surround Fomalhaut and several other young stars remain stable because small planets are constantly forming inside them, according to an article in the Astronomical Journal.
“The narrow boundaries of these rings have always been a mystery to us - as a rule, newborn star systems are not so orderly. Usually, matter in them moves in a chaotic manner until all the 'debris' is swept out and the planets settle in their constant orbits, like the Earth and other celestial bodies of the solar system,”says Carey Lisse of Johns Hopkins University (USA).
Over the past ten years, astronomers have discovered several extremely unusual structures in a number of newborn and young stars, which can be roughly called cosmic analogs of the "eye of Sauron" from Tolkien's books. They are very narrow and dense rings of gas, dust and comets that revolve around stars at very great distances.
Many of these rings, astronomers recently discovered, are often very close to each other. At the same time, they remain stable and do not disintegrate, which suggests that they could not be generated by large planets living in the intervals between the rings, and that some other celestial bodies keep them from "spreading".
Lisse and his colleagues have uncovered the secret of the formation of such cosmic "cometary rings" by studying images taken by the IRTF and Jiminy telescopes, as well as NASA infrared observatories, while observing three newborn star systems - Fomalhaut, HD 32297 in the constellation Orion and HR 4796A in constellation Centaurus.
According to Lisse, initially planetary scientists believed that the real "lord" and creator of these rings could be especially large exoplanets, which formed in the intervals between swarms of comets and imperceptibly "orchestrated" their movement.
New photographs of these rings around three stars, he said, cast doubt on this idea - in that case, some of the comets would inevitably fall to the surface of these "super-earths" and crash, creating huge clouds of dust and gas that should have been visible on infrared and optical photographs of these rings. Scientists did not find anything like this, which made them reject this hypothesis.
What then could have given rise to these rings? Planetary scientists found the answer to this question by analyzing the chemical composition and temperature of the rings orbiting the star HR 4796A. Inside it, they found dozens of comets, as well as several regions heated to about a thousand Kelvin and containing "pure" atoms of some chemical elements, which is an extremely unusual thing for cometary rings.
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On the other hand, relatively high temperatures and a similar chemical composition, according to the researchers, are characteristic of another class of objects - small protoplanets formed as a result of the collision of large asteroids or several comets.
Accordingly, if in a given ring there are several tens of such "embryos", then, as the calculations of scientists show, they should capture all the matter ejected during comet collisions and keep the rings from decaying.
Ultimately, these "embryos" will unite into mini-planets, whose mass is enough to form a full-fledged analogue of the Earth or even larger planets. Scientists believe that similar processes could occur in the early solar system, and they would well explain some of the oddities in the behavior and chemical composition of Uranus and Neptune, as well as how "super-earths" arise in relatively elderly exoplanetary systems.
