A team of astronomers, led by researchers at the Instituto de Astrofísica de Canarias (IAC), may have unraveled the mystery behind the birth of some of the brightest and hottest stars in the cosmos, known as blue supergiants. These stars are at least 10,000 times brighter, two to five times hotter, and 16 to 40 times more massive than the sun. Despite their extreme characteristics, blue supergiants are commonly observed throughout the universe, which has puzzled scientists for decades.
The Mystery of Blue Supergiants
Blue supergiants are often found alone, without a gravitationally bound companion star. This is unusual as the more massive a star is, the more likely it is to have a companion. Around 50% of stars the size of the sun have a companion, but around 75% of much more massive stars are accompanied. However, blue supergiants, some of the most massive stars, are lonely. The reason for this may be that blue supergiant stars exist in systems in which the occupants have already spiraled together, collided, and merged.
Investigating the Origins
The team of scientists set about investigating this by analyzing 59 early B-type blue supergiants located in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, and creating novel stellar simulations. “We simulated the mergers of evolved giant stars with their smaller stellar companions over a wide range of parameters, taking into account the interaction and mixing of the two stars during the merger,” said study leader and IAC researcher Athira Menon.
Findings and Implications
The team’s findings suggest that blue supergiants slip into an evolutionary gap in conventional stellar physics — a phase of stellar evolution where astronomers would not expect to see stars. “Remarkably, we found that stars born from such mergers have greater success in reproducing the surface composition, particularly the nitrogen and helium enhancement, of a large fraction of the sample than conventional stellar models,” said team member and IAC researcher Danny Lennon. “This indicates that mergers may be the dominant channel to produce blue supergiants.”
The new results could represent a large step toward solving a lingering problem regarding the birth of blue supergiant stars, also indicating the importance of binary star mergers in shaping the stellar populations and overall shapes of galaxies.
Future Research
The next step in this research will see the team switch attention from the birth of blue supergiant stars to the death of these massive objects. The scientists will investigate how the supernova explosions of blue supergiant stars create neutron stars and black holes.
