ESO reveal most massive stars have companions

Small stars are sucking energy from their giant counterparts


ESO/M. Kornmesser/S.E. de Mink

'Vampire stars' leach hydrogen from much larger companions

It appears that even some of the biggest, most brutish objects in the Universe can’t live without company. According to a new study using ESO’s Very Large Telescope (VLT), almost 75 per cent of incredibly large and bright O-type stars – the giants responsible for the evolution of galaxies – have a close companion star, a figure far higher than previously thought.

Furthermore, the vast majority of these pairs are interacting with one another, transferring mass from one star to the other – known as the 'vampire star' phenomenon – with a third of them even expected to merge into a single star.

Although O-type stars only make up a small percentage of the stars in the Universe, they have a major effect on their surroundings. The winds and shocks coming from these stars can directly affect star formation. Their radiation also powers the glow of bright nebulae, their supernovae enrich galaxies and they are associated with gamma-ray bursts, which are among the most energetic phenomena in the Universe. These stellar giants have a pivotal role to play in the evolution of galaxies.

Astronomers studied a sample of 71 O-type single stars and binary stars located in six nearby young star clusters in the Milky Way.

By analysing the light coming from these stars in greater detail than ever before, the team discovered that 75 per cent of all O-type stars exist inside binary systems. This is a far higher proportion than previously thought, and the first precise determination of this number. On top of this, the team discovered that the proportion of these pairs close enough to interact is far higher than anyone had thought.

The existence of this large number of vampire stars fits well with a previously unexplained phenomenon. Around a third of stars that explode as supernovae are known to have surprisingly little hydrogen in them. However, the proportion of hydrogen-poor supernovae closely matches the proportion of vampire stars found by this study. Vampire stars are expected to cause hydrogen-poor supernovae in their victims, as the hydrogen-rich outer layers are torn off by the vampire star’s gravity before the victim has a chance to explode as a supernova.

This new investigation will provide scientists with a greater understanding of the life cycles of O-type stars, which could eventually change our view of galaxy evolution, as they play such an important part in this process.



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