Vampire star and its victim

Using ESO’s Very Large Telescope (VLT) astronomers has shown that most very bright high-mass stars, which drive the evolution of galaxies, do not live alone. Many of such binaries transfer mass from one star to another, a kind of stellar vampirism depicted in this artist’s impression.   Image credit: ESO/M. Kornmesser/S.E. de Mink

Almost three quarters of these stars are found to have a close companion star, far more than previously thought.

Surprisingly most of these pairs are also experiencing disruptive interactions, such as mass transfer from one star to the other, and about one third are even expected to ultimately merge to form a single star. The results are published in the 27 July 2012 issue of the journal Science.

The Universe is a diverse place, and many stars are quite unlike the Sun. An international team has used the VLT to study what are known as O-type stars, which have very high temperature, mass and brightness. These stars have short and violent lives and play a key role in the evolution of galaxies. They are also linked to extreme phenomena such as “vampire stars”, where a smaller companion star sucks matter off the surface of its larger neighbour, and gamma-ray bursts.

These stars are absolute behemoths,” says Hugues Sana (University of Amsterdam, Netherlands), the lead author of the study. “They have 15 or more times the mass of our Sun and can be up to a million times brighter. These stars are so hot that they shine with a brilliant blue-white light and have surface temperatures over 30 000 degrees Celsius.

The astronomers studied a sample of 71 O-type single stars and stars in pairs (binaries) in six nearby young star clusters in the Milky Way. Most of the observations in their study were obtained using ESO telescopes, including the VLT.

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