April 17, 2013
Astronomers Locate Massive Binary Star In The Large Magellanic Cloud
April Flowers for redOrbit.com - Your Universe Online
A team of astronomers, led by Hugues Sana of the University of Amsterdam, has observed a binary star that potentially weighed 300 to 400 times the mass of our Sun at its birth.The present day combined mass of the two stars is between 200 and 300 times the solar mass, depending on its evolutionary stage. This makes it potentially the most massive binary star discovered to date. The findings of this study have been published in Monthly Notices of the Royal Astronomical Society Letters.
The star, R144, is found in the outer area of the star nursery region 30 Doradus in the Large Magellanic Cloud. In the center of that region, a number of particularly bright stars with a characteristic pattern of spectral lines can be found. These so-called Wolf-Rayet stars - which are hot, massive stars with a high rate of mass loss - have masses up to 250 times that of our Sun. R144 is the brightest light source of this type in the 30 Doradus region, with a strong emission of X-rays as well, which suggested to the researchers that R144 is a binary system. Due to the discovery of periodic, orbital changes in the spectrum, this suggestion has been confirmed.
The team obtained spectra of R144 using the X-shooter spectrograph on the Very Large Telescope at the European Southern Observatory (ESO) in Chile. Able to observe light from the near-ultraviolet to the near-infrared in one shot, the X-shooter is one of the most sensitive spectrographs on Earth.
“The identification of this candidate would have been a great challenge without X-shooter. This spectrograph makes observations a lot easier and much more efficient, especially because less observation time is required to cover a large spectral range,” explains Sana.
The spectrum of a star can be thought of like its fingerprint. The changing shape and position of the spectral lines makes it clear that R144 is a binary star formed by two hydrogen-rich Wolf-Rayet stars with similar masses. Before this discovery, NGC 3603-A1 was known as the most massive binary star, with a total mass of 212 times the mass of the Sun.
“It is a mystery how extremely massive stars form,” explains Frank Tramper of the University of Amsterdam. “According to the most widely accepted theories, stars of hundreds of solar masses can only form in massive star clusters. The fact that R144 lies far out from the central star cluster in 30 Doradus is possibly an indication that these systems can form in isolation.”
“There is an alternative scenario for the formation of R144,” says Alex de Koter, “namely, that R144 was formed in the central star cluster, but that it was ejected by dynamical interactions with other massive stars.”
The team intends to continue their research with follow-up observations to determine if R144 is a "runaway" star. They also want to definitively establish its mass and other physical properties, in order to decide if R144 is truly the most massive double star ever discovered.