Double star discovered with sand ring

First direct observation of a particle ring in the earth's distance

Double star system KH-15D © Rice University
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For the first time, astronomers have discovered grit-like grains in orbit around a star system. As they report in "Nature", the particles orbit a young binary star at a distance similar to the Earth's sun. They could represent the beginning of planet formation.

In previous studies, astronomers had already succeeded in detecting microscopic dust particles around distant stars. But for more information, the accuracy of this method is insufficient. Therefore, the size of these particles as well as whether they orbit their central star relatively close to that of the Earth, or rather at a distance that corresponds to the orbit of a Jupiter or Saturn, was open.

"When and how planets are formed is still an open question, " explains Christopher Johns-Krull, professor of astronomy and physics at Rice University and co-author of the study. "We believe that the disk-shaped clouds of dust condense around young stars, form microscopic grains of sand and then aggregate into pebbles, chunks and eventually entire planets."

Double star with unusual lighting behavior

Whether this really is the case could help the new study of scientists from the USA, Germany and Uzbekistan now clarify. They analyzed photometric and spectrographic data collected over the past 12 years from various observatories, including the Very Large Telescope in Chile and the Keck Observatory in Hawaii.

Star pair in the constellation Monocerus © Rice University

They came across a strange reflection around a pair of stars in the constellation Monocerus. The double star system KH-15D, which is about 2, 400 light-years away from Earth, is around three million years old and thus still very young according to cosmic standards. "We became aware of this because at different times this system shines brightly and sometimes weak, which is strange, " explains Johns-Krull. It quickly became apparent that a ring of tiny particles of sand was responsible for the changing brightness. display

Orbit comparable to the earth

Viewed from Earth, this particle ring permanently obscures one of the two stars, but the other star moves in an elliptical orbit and therefore emerges periodically behind the sand ring. "These obscurations have enabled us to study the system with the star and without it, " the astronomer says. "This is a good fortune for us, because if the star were visible all the time, it would be so bright that we could not see the sand."

The astronomers were able to determine that the sand ring actually orbits the two stars at a distance roughly equivalent to Earth orbit. And further information could still reveal the favorable arrangement. "Because of the way the light is reflected, there are now ways to make observations on the chemical composition of these sand-like particles, " explains William Herbst of Wesleyan University in Connecticut. This is very exciting because it opens many doors for new research opportunities.

(Rice University, 13.03.2008 - NPO)