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Astronomers discover first Thorne-ytkow object, a bizarre type of hybrid star | CU Boulder Today | University of Colorado Boulder

A joint news release of CU-Boulder and Lowell Observatory

In a discovery decades in the making, scientists have detected the first of a theoretical class of stars first proposed in 1975 by physicist Kip Thorne and astronomer Anna ytkow. Thorne-ytkow objects (TOs) are hybrids of red supergiant and neutron stars that superficially resemble normal red supergiants, such as Betelgeuse in the constellation Orion. They differ, however, in their distinct chemical signatures that result from unique activity in their stellar interiors.

TOs are thought to be formed by the interaction of two massive starsa red supergiant and a neutron star formed during a supernova explosionin a close binary system. While the exact mechanism is uncertain, the most commonly held theory suggests that, during the evolutionary interaction of the two stars, the much more massive red supergiant essentially swallows the neutron star, which spirals into the core of the red supergiant.

While normal red supergiants derive their energy from nuclear fusion in their cores, TOs are powered by the unusual activity of the absorbed neutron stars in their cores. The discovery of this TO thus provides evidence of a model of stellar interiors previously undetected by astronomers.

Project leader Emily Levesque of the University of Colorado Boulder, who earlier this year was awarded the American Astronomical Societys Annie Jump Cannon Award, said, Studying these objects is exciting because it represents a completely new model of how stellar interiors can work. In these interiors we also have a new way of producing heavy elements in our universe. You've heard that everything is made of star stuffinside these stars we might now have a new way to make some of it.

The study, accepted for publication in the Monthly Notices of the Royal Astronomical Society Letters, is co-authored by Philip Massey, of Lowell Observatory in Flagstaff, Arizona; Anna ytkow of the University of Cambridge in the U.K.; and Nidia Morrell of the Carnegie Observatories in La Serena, Chile.

The astronomers made their discovery with the 6.5-meter Magellan Clay telescope on Las Campanas, in Chile. They examined the spectrum of light emitted from apparent red supergiants, which tells them what elements are present. When the spectrum of one particular starHV 2112 in the Small Magellanic Cloudwas first displayed, the observers were quite surprised by some of the unusual features. Morrell explained, I dont know what this is, but I know that I like it!

When Levesque and her colleagues took a close look at the subtle lines in the spectrum they found that it contained excess rubidium, lithium and molybdenum. Past research has shown that normal stellar processes can create each of these elements. But high abundances of all three of these at the temperatures typical of red supergiants is a unique signature of TOs.

I am extremely happy that observational confirmation of our theoretical prediction has started to emerge, ytkow said. Since Kip Thorne and I proposed our models of stars with neutron cores, people were not able to disprove our work. If theory is sound, experimental confirmation shows up sooner or later. So it was a matter of identification of a promising group of stars, getting telescope time and proceeding with the project.

The team is careful to point out that HV 2112 displays some chemical characteristics that dont quite match theoretical models. Massey points out, We could, of course, be wrong. There are some minor inconsistencies between some of the details of what we found and what theory predicts. But the theoretical predictions are quite old, and there have been a lot of improvements in the theory since then. Hopefully our discovery will spur additional work on the theoretical side now.

This work was partially supported by NASA and the National Science Foundation.

Read the full study at

Science Contacts:

Emily Levesque, CU-Boulder, Philip Massey, Lowell Observatory,

Media Contacts:

Laura Snider, CU-Boulder, Kevin Schindler, Lowell Observatory, 928-233-3210 (daytime), 928-607-1387 (nights/weekends)

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