Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Mystery of R Coronae Borealis and other helium stars solved

25.03.2002


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".

Dr Simon Jeffery | alphagalileo
Further information:
http://www.arm.ac.uk/~csj/movies/merger.mpg

More articles from Physics and Astronomy:

nachricht SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute

nachricht New survey hints at exotic origin for the Cold Spot
26.04.2017 | Royal Astronomical Society

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Scientist invents way to trigger artificial photosynthesis to clean air

26.04.2017 | Materials Sciences

Ammonium nitrogen input increases the synthesis of anticarcinogenic compounds in broccoli

26.04.2017 | Agricultural and Forestry Science

SwRI-led team discovers lull in Mars' giant impact history

26.04.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>