Merging of stars to Thorne-Zytkow Objects creates stellar show
By Amanda Jermyn

Back in 1975 Dr. Anna Zytkow of Cambridge University and Dr. Kip Thorne of Caltech predicted the existence of a bizarre type of star within a star, which became known as a Thorne-Zytkow Object. Just earlier this year an unusual hybrid star was observed that fits this description and helps confirm their theory.

Using the 21.3 foot Magellan Clay telescope in Chile, a team of astronomers led by Dr. Emily Levesque of the University of Colorado Boulder, and including Dr. Zytkow, discovered what at first appeared to be a red supergiant star, HV2112, in the Small Magellanic Cloud.

The difficulty in finding Thorne-Zytkow Objects is that they superficially resemble red supergiants, the largest type of star by volume, but not by mass. However, a detailed analysis of the spectrum of a star (the characteristics of the electromagnetic radiation it emits) can help clarify what kind of star it is. In the case of HV2112, the object observed by Dr. Levesque’s team, the unusual features of its spectrum led them to conclude that what they were in fact seeing was likely a Thorne-Zytkow Object or TZO.

A TZO results from the merger of a neutron star with a red supergiant in a binary system. A neutron star is a super-dense object formed during a supernova when a massive star collapses under gravity after burning all its nuclear fuel. The merger of the neutron star and red supergiant creates an exotic new system consisting of a neutron star surrounded by a large diffuse envelope of material.

In theory, Thorne-Zytkow Objects are expected to emit signals indicating an abundance of the elements lithium, molybdenum and rubidium, as indeed occurred with HV2112. However, as these elements were detected in slightly lower quantities than expected, further analysis will be necessary to confirm that the new discovery is in fact a Thorne-Zytkow Object.

According to Dr. Levesque, “Studying these objects is exciting because it represents a completely new model of how stellar interiors can work.” A normal red supergiant is powered by nuclear fusion in its core. However, while a Thorne-Zytkow Object is mostly powered by thermonuclear energy produced at the core of the envelope of material, a small amount of its energy derives from the gravitational accretion of material from the envelope onto the neutron star. The unusual interactions in the interiors of these stars result in heavy elements produced in ways not seen before.

Astronomers think it likely that several Thorne-Zytkow Objects exist within our own galaxy, the Milky Way. Hopefully the discovery and detailed study of such objects will provide new insights into our weird and wonderful universe.

Join the Springfield Stars Club on Tuesday, October 28th at 7pm (please note earlier starting time) at the Springfield Science Museum for a talk by Dr. David Wexler on “Cosmology.” Dr. Wexler will discuss how astrophysicists model the large-scale structure and evolution of the universe. A Stars Club board member, Dr. Wexler studied neuroscience and engineering at Case Western Reserve University, and completed medical studies at Stanford University. He works as an ear, nose and throat specialist at Baystate Wing Hospital in Palmer. Dr. Wexler has a Master’s degree in astronomy and is currently a distance-learning student in astronomy-physics with Open University, UK. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.

Also, on Friday, November 7th, the Stars Club and Springfield Science Museum will host “Stars over Springfield.” Dave Gallup will speak on “Splendors of the Autumn Night Sky.” Gallup is president of the Naturalist Club and a past president of the Stars Club. A fee of $3 for adults and $2 for children under 18 will be charged.