Rare properties of young binary star system determined for first time

Using NASAs Far Ultraviolet Spectroscopic Explorer (FUSE) satellite and ground-based telescopes, astronomers have determined, for the first time, the properties of a rare, extremely massive, and young binary star system.

Washington, May 29 : Using NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) satellite and ground-based telescopes, astronomers have determined, for the first time, the properties of a rare, extremely massive, and young binary star system.

The system, known as LH54-425, is located in the Large Magellanic Cloud, a satellite galaxy of our Milky Way.

According to Georgia State University Astronomer Stephen Williams, who obtained the spectra of the system at the 1.5 metre telescope at the Cerro Tololo Inter-American Observatory in Chile, the binary consists of two O-stars, the most massive and luminous types of stars in the Universe.

The more massive star is shedding material at a rate of 500 trillion tons per second with a speed of 5.4 million miles per hour. This is about 400 times greater than the rate the sun loses mass through the solar wind. The smaller star is ejecting mass at about one-tenth the rate of its sibling.

The mass loss rate of both stars though is consistent with other single stars having the same temperature and luminosity, said Rosina Iping of the Catholic University, Washington and NASA Goddard Space Flight Center, Greenbelt, and leader of the team that observed LH54-425 with FUSE.

The spectra also revealed the two stars to contain about 62 and 37 times the mass of our Sun.

"The stars are so close to each other -- about one-sixth the average Earth-Sun distance -- that they orbit around a common centre of mass every 2.25 days. With a combined mass of about 100 suns, the system is one the most extreme binaries known. The stars are probably less than 3 million years old," said Williams' colleague Douglas Gies of Georgia State University, Atlanta.

According to the researchers, each star blows off a powerful stellar wind, and FUSE's observations have provided them with the first details of what happens when the two supersonic winds collide.

"The wind collision zone wraps around the smaller star and produces a curved surface of superheated gases that emit X-rays and far-ultraviolet radiation. FUSE is ideal for these measurements because the lines that best indicate the properties of stellar winds show up in the far ultraviolet part of the spectrum, where FUSE is most sensitive," said Williams.

FUSE project scientist George Sonneborn of NASA Goddard Space Flight Center, Greenbelt, Md. said the "merger of two massive stars to make a single super star of over 80 suns could lead to an object like Eta Carinae, which might have looked like LH54-425 one million years ago".

Eta Carinae is one of the most massive and luminous stars in the Milky Way Galaxy, with perhaps 100 solar masses.

"Finding stars this massive so early in their life is very rare. These results expand our understanding of the nature of very massive binaries, which was not well understood. The system will eventually produce a very energetic supernova," said Sonneborn.

"These stars are evolving in the blink of an eye compared to the sun, which has looked pretty much the same for over four billion years. But this binary looks totally different from Eta Carinae even though there is maybe only one million years difference in age. These massive stars zoom through their life cycle really fast. Will this binary system produce something like Eta Carinae? We don't know," added Iping.

The findings are being presented at the spring 2007 American Astronomical Society meeting in Honolulu, Hawaii.

ANI