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Strange Hybrid Object Discovered --1st Ever Predicted in 1975

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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 Żytkow. Thorne-Żytkow objects (TŻOs) 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.

TŻOs are thought to be formed by the interaction of two massive stars―a red supergiant and a neutron star formed during a supernova explosion―in 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, TŻOs are powered by the unusual activity of the absorbed neutron stars in their cores. The discovery of this TŻO 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 Society’s 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 stuff’—inside 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 Żytkow 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 star—HV 2112 in the Small Magellanic Cloud―was first displayed, the observers were quite surprised by some of the unusual features. Morrell explained, “I don’t 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 TŻOs.

“I am extremely happy that observational confirmation of our theoretical prediction has started to emerge,” Żytkow 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 don’t 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.

The Daily galaxy via CU-Boulder and Lowell Observatory

Image credit: Image credit: NASA/CORBIS


I don't really understand how a star like this wouldn't collapse into a black hole. red giants already have enough mass to collapse into a black hole or neutron star which brings up the question of how would basically 2 of these stars in terms of mass not collapse unless both were low end mass red giants? Another point is red giants collapse because there is too much iron in the core and the star isn't burning enough so wouldn't a neutron core addition push that even further since neutron stars don't have fusion? Can anyone explain how a star like this can make sense?

In time somebody will either confirm or find an alternative as to what has happened with HV 2112.

May the wonders of our universe continue to unfold.

"red giants already have enough mass to collapse into a black hole or neutron star which brings up the question of how would basically 2 of these stars in terms of mass not collapse unless both were low end mass red giants?"

Stars collapse when the inward force of gravity gets stronger than the outward force of electromagnetism. Stars are relatively small when they burn hydrogen and then balloon to a bigger size when they start burning helium because the hydrogen is exhausted. When even the helium is exhausted, the star suddenly loses the outward force. The inward force, however, is still there - and the star implodes.

Objects don't become black holes because they're so heavy, they become black holes because they're so dense. A star may have easily enough mass to become a black hole, but as long as it is being pushed outward by its own fusion, its density will be way too low. In order for the sun to become a black hole, all of its mass would have to be compressed to a radius of about 3 km (which won't happen because the sun isn't heavy enough, but that's another topic entirely)

mica trieu:

The wiki article seems to have been updated to reflect this news, and explains the answer to your question, I think.–Żytkow_object

The surface of the neutron star at the center of the object is extremely hot, roughly 1 million Kelvin. It is also rotating at over 600 revolutions per second. The temperature and pressure at the interface between the outer core of the star and the small neutron star at the heart of the core are sufficient to sustain the fusion of hydrogen and later helium in the red giant. When the helium runs out, heavier elements will be fused at ever higher temperatures and pressures until the red giant collapses on the fusion star, after which, depending on how much mass remains in the red giant, there will either be a nova or a supernova, with the possibility of a black hole being created at that point.

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