July 26, 2012
The Universe’s Brightest Stars Prefer Company, New Study Finds
Lee Rannals for redOrbit.com - Your Universe Online
The brightest stars in the universe apparently do not like to live alone, according to a new study using ESO's Very Large Telescope (VLT).
Nearly three-quarters of the brightest, high mass stars are found to have a close companion star, which is far more than previous thought.
Most of these pairs of stars are also experiencing disruptive interactions, like mass transfer from one star to the other. Another third of them are expected to ultimately merge to form a single star.
A team used the VLT to study a star variety known as O-type, which have a very high temperature, mass and brightness. These stars have short and violent lives and play a key role in the evolution of galaxies.
The stars are also linked to extreme phenomena like "vampire stars," which is when a smaller companion star sucks matter off the surface of its larger companion star.
“These stars are absolute behemoths,” Hugues Sana, the lead author of the study published in the journal Science, said in a press release. “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 stars and stars in pairs in six nearby young star clusters in the Milky Way. Most of the observations were obtained using ESO telescopes.
The team discovered that 75 percent of all O-type stars exist inside binary systems, which is a higher proportion than what scientists previously thought.
They also found that the proportion of these pairs that are close enough to interact is higher than anyone had thought before.
O-type stars make up only a fraction of a percent of the stars in the Universe, but the violent phenomena associated with them leaves them with a disproportionate effect on their surroundings.
"The winds and shocks coming from these stars can both trigger and stop star formation, their radiation powers the glow of bright nebulae, their supernovae enrich galaxies with the heavy elements crucial for life, and they are associated with gamma-ray bursts, which are among the most energetic phenomena in the Universe," ESO wrote in a press release.
Selma de Mink of Space Telescope Science Institute and a co-author of the study says 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 neighbor," de Mink said in a press release.
Mergers between stars can be violent events that will be the end of around 20 to 30 percent of O-type stars. However, the vampire stars, which account for 40 to 50 percent of cases, have a large effect on how these stars evolve.
Astronomers mostly considered that closely-orbiting massive binary stars were the exception, which is something that only needed to explain phenomena like X-ray binaries, double pulsars and black hole binaries.
The study published in Science shows that in order to properly interpret the Universe, scientists must understand that these double stars are not just common, but their lives are fundamentally different from those of single stars.
In the case of vampire stars, the lower-mass star is rejuvenated as it sucks the fresh hydrogen from its companion. The stars mass will increase substantially and will outlive its companion, surviving much longer than a single star of the same mass would. The star that becomes the vampire star's victim is stripped of its envelope before it has a chance to become a luminous red super giant.
Ultimately the stellar population of a distant galaxy may appear to be much younger than it really is, because the effects of a vampire star leaves the pair mimicking the appearance of younger stars.
“The only information astronomers have on distant galaxies is from the light that reaches our telescopes," Sana said in a press release. "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."
He said this study shows that the assumption that most stars are single can lead to the wrong conclusions when observing the universe.