A collaborative research team from the Universities of Tübingen and Potsdam have discovered a new star type whilst searching for ‘hot stars.’
How did the research team come across this new star?
Scientists discovered this new star type whilst searching for ‘hot stars’ with the Large Binocular Telescope in Arizona, in an attempt to better understand the final stages of stellar evolution.
The conventional life cycle of a star, like our Sun, begins with the nuclear fusion of hydrogen into helium. Then, deep inside the incandescent body, a nuclear reaction begins that converts helium into carbon and oxygen. The star ‘dies’ in the course of millions of years and shrinks to a white dwarf.
Thus, normal stellar surfaces are composed of hydrogen and helium. However, these stars, found under the direction of Professor Klaus Werner of the University of Tübingen, are wrapped in carbon and oxygen – the ash of a helium nuclear fusion.
This unusual composition is all the more perplexing because the temperatures and diameters of the incandescent bodies indicate that helium nuclei continue to fuse inside them. Scientists have noted the presence of objects covered with carbon and oxygen instead of hydrogen; the cause is proposed to be an explosive resumption of helium fusion, which then brings the burning ash – carbon and oxygen – to the surface.
Werner explained: “We normally expect stars with the chemical surface composition of the stars discovered to have completed the helium fusion in their centres and to be in the final stages of becoming white dwarfs.
“However, this event cannot explain these newly discovered stars. They have larger radii and carry out helium fusion peacefully at their centres.”
How are scientists explaining the existence of this incandescent body?
A potential explanation for the formation of these new incandescent bodies is provided by a parallel paper published by astronomers at the University of La Plata, conducted by Marcelo Miller Bertolami: “We believe that the stars discovered by our German colleagues were formed by a very rare type of merging between two white dwarfs,” commented Bertolami.
The merger of white dwarfs in close binary star systems can occur because the distance between their orbits is constantly decreasing due to the emission of gravitational waves. Nicole Reindl of the University of Potsdam concluded: “This does not normally lead to the formation of a star enriched in carbon and oxygen. However, we believe that in binary systems with very specific stellar masses, a white dwarf with a carbon-oxygen core can be ripped apart by tidal forces.
“Its material is then dumped on the surface of its white dwarf companion, leading to the formation of these exotic stars.”
However, scientists have noted that more detailed evolutionary models are needed to fully explain the phenomenon.
These results have been published in the Monthly Notices of the Royal Astronomical Society.