The Beginnings of a Supermassive Star?
Title: MY Camelopardalis, a very massive merger progenitor
Authors: J. Lorenzo, I. Negueruela, A.K.F. Val Baker, M. García, S. Simón-Díaz, P. Pastor, M. Méndez Majuelos
At 13,000 light years away, MY Camelopardalis (MY Cam) is the brightest stellar object in the open cluster Alicante 1. Since its initial discovery, MY Cam was later identified to be a binary star, consisting of two O-type stars that orbit around each other. MY Cam is one of the most massive binary star systems, and studying it provides insight into the theory of how extremely massive single stars are formed.
The authors used spectroscopic data, obtained in 2004, and photometric data, obtained in 2008, to determine the properties of the two stars. The primary star is the largest and hottest of the two, with a temperature of 42,000K and a mass 37.7 times greater than our Sun. The secondary star is 39,000K and has a mass 31 times the Sun. They are both early O-type main sequence stars.
By studying the light curve, the authors found that MY Cam has a short period of a little over one day. With such a fast orbit, these massive stars must be so close together that they are touching. This is known as a contact binary, and MY Cam is one of the largest. In addition, the two stars eclipse one another from our point of view, making MY Cam an eclipsing binary.
It was found that these close binary stars were overfilling their Roche lobes, the region around a star where matter is gravitationally bound to it. As a result, mass from the smaller star is being transferred to the larger one. The fate of these two stars is unknown, but it is likely the two stars will merge into a single, very massive star. There isn’t much insight into massive stellar mergers. Observations are limited to non-massive binary systems and models of their evolution just don’t exist. But based on theoretical predictions, the authors suggest that this merger will result in a single massive star that will have very unusual properties.
Image: The open cluster Alicante 1. The binary star MY Cam is circled in blue. (Credit: Ignacio Negueruela and Javier Lorenzo)
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