Discovery challenges theory about rejuvenated stars

Tuesday, September 10, 2013

The discovery shows that blue stragglers -stars that appear to be younger than how they really are- would form by a process of stellar cannibalism between binary stars and not by stellar collisions in low density environments.

Study was led by Felipe Santana and Ricardo Muñoz, astronomers from Universidad de Chile and researchers from the Center for Excellence in Astrophysics and Associated Technologies (CATA). A group of North American and european astronomers were also collaborating in this research.

The discovery

“We found blue stragglers in different stellar groups and galaxies in which the huge separation between their stars make impossible for them to collide with each other. Thus, we provided unprecedented evidence favoring another blue straggler formation theory that would not be related to collisions but with a slow merge or mass-transfer between stars that are born together, called binaries. Our data shows that collisions are not only unnecessary for blue straggler formation in low density environments, but furthermore, they seem to prevent binaries to form this unique type of stars. The next step of this research would be to determine the detail of how these stars could end up merging or transferring material to form a blue straggler.” Explains Felipe Santana, Ph.D. student from the Astronomy Department at Universidad de Chile.

What are blue stragglers

Blue stragglers are stars unusually hot, that show temperatures higher than others with similar characteristics, which is why they are bluer. This objects have the peculiarity that took longer to evolve than their pairs, and thus astronomers believe that at some point in their lives, these stars received an external input of mass. This extra mass would allow “blue stragglers” to keep producing energy and light for more time, which make them look younger than what they really are.

The original theory stated that blue stragglers obtained this fuel injection from a stellar collision that happened in the past. Which is why we used to believe that this objects could only exist in environments where a stellar collision could occurred.

Binary Stars

These stars are the ones that are formed from the same gas cloud and once born orbit each other because they are gravitationally bound. This pair of stars display the same age and composition, although they often differ in mass.

How it was done

The research took 2 years of work and half-dozen astronomers that analyzed the data. The investigation used data from the Canada-France-Hawaii telescope, located at the big Hawaiian Island. “Images from the telescope corresponded to different galaxies and stellar groups from the outer regions of the Milky Way, i.e., at distances several million times the distance from the Earth to our Sun. For each object in our sample we look for stars that were unusually blue, and hence, potential blue stragglers and then we studied their properties.” Says Santana.

“Later on, we will try to complement this work with images that are already taken at the Magellan II telescope, located at Cerro las Campanas in the north of Chile. This way we are going to have data from both hemispheres, which will allow us to access to different regions of the sky and obtain a complete sample.” Explains Ricardo Muñoz.