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 Space radiation won't stop NASA's human exploration
18.10.2017 | NASA/Johnson Space Center

nachricht Study shows how water could have flowed on 'cold and icy' ancient Mars
18.10.2017 | Brown University

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: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Osaka university researchers make the slipperiest surfaces adhesive

18.10.2017 | Materials Sciences

Space radiation won't stop NASA's human exploration

18.10.2017 | Physics and Astronomy

Los Alamos researchers and supercomputers help interpret the latest LIGO findings

18.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>