Sand clouds reveal the age of brown dwarfs

(ORDO NEWS) — Archival data from the Spitzer telescope made it possible to examine clouds of silicate particles in the atmospheres of dozens of brown dwarfs and determine the conditions under which such “sand clouds” arise.

Clouds form not only in the earth’s atmosphere, but also on many other celestial bodies. They can be very different from the clubs of water vapor we are used to.

For example, in the hydrogen atmosphere of Jupiter, clouds are formed by ammonia, and on the hot exoplanet MASCARA-2, by iron and other metals.

Clouds are also known on brown dwarfs – objects that occupy an intermediate position between the largest planets and the smallest full-fledged stars.

They are the subject of a new paper by Genaro Suárez and Stanimir Metchev from the University of Western Ontario in Canada.

Back in the 2000s, observations with the Spitzer telescope showed that brown dwarf clouds are composed of particles of silicate minerals – quartz and olivine, like the sand we are used to.

Such “sand clouds” have been found on only a few dwarfs, although theoretically they should be much more common.

Therefore, astronomers recently turned to archival images of the already completed Spitzer and analyzed data on all small stars and brown dwarfs that fell into his lens – a total of 113 objects.

Indeed, “sand clouds” have been found on most brown dwarfs. However, these data made it possible to trace a new curious dependence.

In dwarfs heated above 1700 ° C, clouds are not observed: their atmospheres are too hot, and even silicates are present in them in gaseous form.

Clouds of these silicates are found in cooler brown dwarfs, and the maximum “cloudiness” reaches at 1300 °C. Finally, in dwarfs with temperatures below 1000 ° C, clouds are again not visible: they go to the depths of their atmospheres.

The temperature of a brown dwarf may indicate its age. Thermonuclear reactions on them never reach such strength to compensate for energy losses, so young dwarfs are hot, but cool down over time.

Judging by the new data, these “age-related changes” should also affect the cloudiness in the atmosphere. Newborn dwarfs are not yet cool enough for particles of “sand clouds” to condense here. Gradually, conditions become more suitable until the already old dwarf is too cold to be cloudy.

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