Glassy galaxies

Clouds of sand crystals resembling crushed glass envelop 21 infrared-bright galaxies, astronomers report.

Observed by NASA’s infrared Spitzer Space Telescope, the silicate crystals are the first recorded beyond the Milky Way. The galaxies that the crystals coat are known as ultraluminous infrared galaxies and are the product of a collision of two or more spiral galaxies.

Shock waves from the galaxy mergers triggered the birth of a huge population of massive stars, which ended their short lives in titanic explosions called supernovas, says Henrik Spoon of Cornell University. He and his colleagues propose in the Feb. 20 Astrophysical Journal that the silicate crystals were produced by the stars just before or during their explosions. Because the glassy crystals are fragile, they would quickly transform into an amorphous structure, say the researchers.

That suggests that Spitzer spotted the crystalline silicates around 21 of 77 infrared-bright galaxies because the craft looked at just the right time and the galaxies produced copious amounts of material. The team speculates that the galaxies that showed no evidence of the crystals either hadn’t yet produced much of the material or had already converted it to a noncrystalline form.

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