Most of the very bright large stars do not live alone but with another tiny star. Scientists have found that the majority of tiny companion stars act as a "vampire", as they suck the life energy or essential gases from the larger companion, according to a European Space Agency report.
Using the ESO's Very Large Telescope (VLT), an international team of scientists discovered the vampire stars while studying O-type stars which have high temperatures, mass and brightness compared to the sun.
"These stars are absolute behemoths. 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," said Hugues Sana, researcher at the University of Amsterdam.
Scientists had studied 71 O-type single stars and stars in pairs (binaries) in six nearby young star clusters in the Milky Way.
The study found that the vampire stars are relatively smaller and of lower mass compared to other stars. The vampire stars rejuvenate themselves as they suck hydrogen from their companion stars. In the process their mass increases substantially making them outlive their companions.
Scientists claim that the vampire stars survive much longer than a single star with the same mass would. However, the victim star becomes a red giant instead of a blue hot core.
As a result, the stellar population of a distant galaxy may appear to be much younger than it is because of the rejuvenated vampire stars that become hotter and bluer in colour, mimicking the appearance of younger stars.
"The life of a star is greatly affected if it exists alongside another star. If two stars orbit very close to each other they may eventually merge. But even if they don't, one star will often pull matter off the surface of its neighbour," said Selma de Mink, researcher at the Space Telescope Science Institute."
Previously, scientists believed that there were only a few blue giant stars in our galaxy, but now the team has discovered that there are more blue giants. Almost three-quarters of these stars are found to have a close companion star, far more than previously thought.
Understanding how big these effects are, and how much this new perspective will change our view of galactic evolution. Scientists claim that further studies will help them know the true mass of these stars.
"The only information astronomers have on distant galaxies is from the light that reaches our telescopes. Without making assumptions about what is responsible for this light we cannot draw conclusions about the galaxy, such as how massive or how young it is. This study shows that the frequent assumption that most stars are single can lead to the wrong conclusions," Hugues Sana said.