A study carried out by an international team led by Hugues Sana of the University of Amsterdam in the Netherlands has uncovered through the use of the VLT (Very Large Telescope), and other ESO’s (European Southern Observatory) telescopes that most of the O-type stars are part of binary systems. Even more, usually, one of two stars acts like a vampire sucking matter from its companion.

O-type stars have masses above 16 times the Sun’s and a  very high surface temperature, higher than 33,000 degrees Kelvin. They’re very bright and because of their color, they’re called blue giants. Because of their mass, the temperatures in their core are so high that they run out of hydrogen in a very short time from an astronomical point of view, even a few million years. Also for this reason, they represent a small percentage of the existing stars in the universe.

A sample of 71 O-type stars has been under observation for this study. These stars belong to six clusters in the Milky Way. It was found that 75% of these stars belong to binary systems, a higher percentage than previously thought. In particular, astronomers have discovered that most of these pairs of stars are close enough to interact with one of the two stars sucking material from its companion. In 20-30% of cases, probably the two stars will eventually merge in a violent event.

In the case of the vampire stars, the companion with a lower mass is rejuvenated by sucking hydrogen from its companion. For this reason, its mass is increased and it will live longer than its companion and more than a single star of the same mass normally lives.

The star to which the hydrogen is “stolen” loses its surface layer of hydrogen before it can become a red giant, leaving its hot core exposed. The consequence is that watching the stars in a galaxy far away, they can look younger than they actually are because both stars have become warmer so they have the color of younger stars.

This study will allow astronomers to get a better idea of how galaxies evolve. This is important because especially the evolution of these giant stars has significant effects on the clusters to which they belong. The phenomena associated with them may in fact start or stop the formation of new stars and the radiation they emit can make nebulae glow.

When these stars explode in supernovae, the elements that are created may help form new planets on which life might arise. We too are partly children of ancient supernovas. O-type stars are also associated with gamma-ray-bursts, where huge amounts of energy are released that can completely sterilize a planet if they hit it. It’s therefore clear that it’s important to understand how these stars live.