Twinkle, twinkle new little star

by Allison Mills
Tuesday, August 19, 2014

A new hybrid star, called a Thorne-Zytkow object, was observed in the Small Magellanic Cloud, one of the closest and brightest galaxies near the Milky Way. Credit: NASA/CXC/JPL-Caltech/STScI.

What’s red, sparkly and far from home? Not Dorothy’s shoes, but a Thorne-Zytkow object (TZO), a type of hybrid star theorized since 1975 to exist but not observed until now.

TZOs are hybrid stars thought to form as a red supergiant star swallows a neutron star. Although the newly seen TZO glows the color of Betelgeuse, a red supergiant, its interior composition is different. Using a 6.5-meter Magellan Clay telescope in Chile, the researchers observed the TZO in the Small Magellanic Cloud, a nearby galaxy about 210,000 light-years away. The researchers noted in the light spectra from the galaxy’s red supergiants that one had a distinct chemical signature: Although the TZO’s temperature is typical of a red supergiant, it has excess rubidium, lithium and molybdenum — not characteristic of these big stars.

The TZO’s chemistry doesn’t perfectly match the theoretical model, however, the researchers pointed out in their study published in the Monthly Notices of the Royal Astronomical Society Letters. “The theoretical predictions are quite old, and there have been a lot of improvements in the theory since then,” said Philip Massey, a co-author and an astronomer at the Lowell Observatory in Flagstaff, Ariz., in a statement. “Hopefully our discovery will spur additional work on the theoretical side now.”

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