Mystery of R Coronae Borealis and other helium stars solved

Astronomers Dr Simon Jeffery of the Armagh Observatory and Dr Hideyuki Saio of Tohoku University, Japan, have finally solved a long-standing mystery concerning the creation of two particular kinds of rare stars. They have found that a class of variable stars named after their prototype R Coronae Borealis (RCrB), and a related group called `extreme helium stars` are the products of mergers between pairs of white dwarf stars. What kind of star results from the merger depends on the composition of the white dwarfs. The research is to be published in the Monthly Notices of the Royal Astronomical Society.

RCrB stars and their hotter cousins, the extreme helium stars, are highly unusual. While most ordinary stars are typically three-quarters hydrogen (by weight), these oddities have hardly any hydrogen on their surfaces. Instead, they are made primarily of helium, with some carbon, traces of hydrogen and other peculiarities. For some time, astronomers have suspected that they are the mixed-up remains from inside old stars, where nuclear fusion has created helium, carbon and other chemical elements. The question has been, how did it happen?

The problem has haunted Simon Jeffery for much of his career. He began studying extreme helium stars about 20 years ago, and his collaboration with Hideyuki Saio started in 1985. A breakthrough came when Jeffery realised that the helium stars are giving out more energy than they produce inside them by nuclear processes. That meant they must be shrinking. Observations he made of four helium stars with the orbiting International Ultraviolet Explorer (IUE) observatory demonstrated that they were getting hotter by 30120 degrees per year. And observations of some pulsating helium stars showed that they are 90% the mass of the Sun.

Saio, an expert on computer modelling, developed the simulations of stellar mergers needed to convince other astronomers that two white dwarfs coming together could explain the observations. It was a difficult job. Conventional thinking said that if you added hydrogen from one white dwarf to another, it would either just be blown away or there would be a supernova explosion. But what would happen if you added helium?

White dwarfs are the cores left over when old, evolved stars blow off their outer layers. They are by no means all the same and their compositions cover a bewildering range. A simulated merger between two helium white dwarfs produced a star matching very closely the properties of a nitrogen-rich helium star called V652 Herculis. A merger between a carbon-oxygen white dwarf and a helium white dwarf matched the shrinking helium stars Jeffery had observed with IUE and explained very well the properties of RCrB stars and extreme helium stars.

“There are still some unanswered questions, though” says Jeffery. “The actual merger, when one white dwarf is ripped apart by its companion, is
likely to be extremely violent, taking a matter of a few minutes. We don`t yet know how the material will be spread out – into a big disk around the star perhaps – or what happens as the new helium star expands by a factor of 10,000″.

Media Contact

Dr Simon Jeffery alphagalileo

Alle Nachrichten aus der Kategorie: Physics and Astronomy

This area deals with the fundamental laws and building blocks of nature and how they interact, the properties and the behavior of matter, and research into space and time and their structures.

innovations-report provides in-depth reports and articles on subjects such as astrophysics, laser technologies, nuclear, quantum, particle and solid-state physics, nanotechnologies, planetary research and findings (Mars, Venus) and developments related to the Hubble Telescope.

Zurück zur Startseite

Kommentare (0)

Schreib Kommentar

Neueste Beiträge

A rich source of nutrients under the Earth’s ice sheets

Data from Greenland and Antarctica show: under ice trace elements are mobilised at higher rates than previously assumed. Trace elements such as iron, manganese and zinc are an integral part…

Life cycle of moon jellyfish depends on the microbiome

Research team at Kiel University uses Aurelia aurita as an example to demonstrate the relationship between microbial colonization and reproduction in marine cnidarians The body tissue of all multicellular living…

Fraunhofer IWM closes gaps in the mechanics of materials digital value chain

The greatest potential of digitalization in companies in which materials play a prominent role lies in the cross-process linking of materials data. This promises to shorten component development times, faster…

By continuing to use the site, you agree to the use of cookies. more information

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.

Close