Tiny crystals in frozen comets are created by outbursts from stars

May 14th, 2009 - 2:35 pm ICT by ANI  

Washington, May 14 (ANI): Astronomers have used NASA’s Spitzer Space Telescope to determine that outbursts from stars create tiny silicate crystals in frozen comets.

Scientists have long wondered how tiny silicate crystals, which need sizzling high temperatures to form, have found their way into frozen comets, born in the deep freeze of the solar system’s outer edges.

The crystals would have begun as non-crystallized silicate particles, part of the mix of gas and dust from which the solar system developed.

Now, a team of astronomers believes they have found a new explanation for both where and how these crystals may have been created, by using NASA’s Spitzer Space Telescope to observe the growing pains of a young, Sun-like star.

The researchers from Germany, Hungary and the Netherlands found that silicate appears to have been transformed into crystalline form by an outburst from a star.

They detected the infrared signature of silicate crystals on the disk of dust and gas surrounding the star EX Lupi during one of its frequent flare-ups, or outbursts, seen by Spitzer in April 2008.

These crystals were not present in Spitzer’s previous observations of the star’s disk during one of its quiet periods.

“We believe that we have observed, for the first time, ongoing crystal formation,” said Attila Juhasz of the Max-Planck Institute for Astronomy in Heidelberg, Germany, one of the research paper’s authors.

“We think that the crystals were formed by thermal annealing of small particles on the surface layer of the star’s inner disk by heat from the outburst. This is a completely new scenario about how this material could be created,” Juhasz added.

Annealing is a process in which a material is heated to a certain temperature at which some of its bonds break and then re-form, changing the material’s physical properties.

The crystals appear to be forsterite, a material often found in comets and in protoplanetary disks.

The crystals also appear hot, evidence that they were created in a high-temperature process, but not by shock heating.

“At outburst, EX Lupi became about 100 times more luminous,” said Juhasz.

“Crystals formed in the surface layer of the disk but just at the distance from the star where the temperature was high enough to anneal the silicate - about 1,000 Kelvin - but still lower than 1,500 Kelvin. Above that, the dust grains will evaporate,” Juhasz added.

The radius of this crystal formation zone, the researchers note, is comparable to that of the terrestrial-planet region in the solar system. (ANI)

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