A group of astronomers led by researcher Gaston Folatelli from the Kavli Institute of Physics and Mathematics of the Universe (IPMU) at the University of Tokyo, in collaboration with experts from the Department of Astronomy (DAS) at the University of Chile and Millennium Institute of Astrophysics (MAS) Mario Hamuy and Hanindyo Kuncarayakti, just found evidence of the last missing piece to explain a supernova discovered in 2011, which would be a yellow supergiant progenitor star.

According to the common theory, which applies to isolated stars, only the coldest and largest (red supergiants) or the hottest and bluest (Wolf-Rayet) stars could become supernovas. The idea that supernova SN 2011dh had as progenitor a yellow supergiant star consequently intrigued the experts. The team led by Folatelli postulated that it was a binary system composed of the yellow star and a companion that had not been found yet.

This theory turned out to be true when IPMU astronomers, in collaboration with MAS, found evidence of the companion through images obtained with the Hubble Space Telescope (HST). It was a bright blue star, the missing link to both corroborate the hypothesis of the research team, and show once again that most massive stars are not lonely, but belong to binary systems with deep interactions.

"Stars are the factories of chemical elements in the Universe. Therefore, to understand how it evolves, we need to know which are the stars that explode as supernovas allowing Earth-like planets to be formed. So far, we have identified a handful of progenitors of supernovae rich in hydrogen (type II), and knew about only one supernova poor in this element (type IIb). This study conclusively reveals a second case of type IIb supernova, that has its origin in a binary system. Therefore, it strengthen the idea that supernovae poor in hydrogen must be due to a companion responsible for 'stealing' this element. We are gradually exploring unknown territories", said Mario Hamuy, researcher at DAS and director of MAS.

Meanwhile, Hanindyo Kuncarayakti, MAS and DAS researcher who was part of the team that analyzed the images, notes that this discovery "introduces strong support for theories beyond the traditional paradigm that exists for supernovae, being important now to seriously consider the scenario of binary systems explaining the evolution of stars and supernovae."

The reason why the discovery of this blue star is so important is that this observation fits extremely well with the predictions made by the investigators. "One of the most exciting moments of my career was when I reduced the HST images that I had just obtained, and saw the object right where we had planned it to be from the beginning. It is the first time we can clearly see the companion, allowing us to study it in more details and determine their properties. The relevance of this finding goes beyond this particular supernova, it allows us to learn more about the connection between massive stars and supernovae", concludes Folatelli.