Neither Star Nor Planet

by | Oct 5, 2004 | Exoplanetary Science

And it’s not a brown dwarf, either. That’s the verdict of astronomers using the Keck II and Gemini North telescopes (supported by observations at Kitt Peak National Observatory), who have been studying a binary system with a difference. One of the stars involved has lost huge amounts of mass, enough that it no longer qualifies as
a star. We do not, in fact, know what to call it.

“Like the classic line about the aggrieved partner in a romantic relationship, the smaller donor star gave, and gave, and gave some more until it had nothing left to give,” says Steve B. Howell, an astronomer with Wisconsin-Indiana-Yale-NOAO (WIYN) telescope and the National Optical Astronomy Observatory, Tucson, AZ. “Now the donor star has reached a dead end – it is far too massive to be considered a super-planet, its composition does not match known brown dwarfs, and it is far too low in mass to be a star. There’s no true category for an object in such limbo.”

EF Eridani

Image: EF Eridanus 500 Million Years Ago. Onset of mass transfer some 500 million years ago when the donor object (right), began losing mass to the compact yet more massive white dwarf companion (left). At the time of this illustration, the star system appeared much brighter in optical light than it does today. Illustration by Jon Lomberg/Credit: Gemini Observatory.

The system, EF Eridanus, is located about 300 light years from Earth. The star in the system is a white dwarf with approximately 60 percent of the mass of the Sun; it is a burnt-out stellar remnant about as big as the Earth, and it is still producing light. The inert object — whatever we choose to call it — has 1/20th the mass of the Sun, and is now roughly the diameter of Jupiter. The two objects are separated by about the same distance as the Earth and the Moon.

“There are about 15 other known binary systems out there that may be similar to EF Eri, but none has been studied enough to tell,” Howell says. “We are working on some of them right now, and trying to improve our models to better match the infrared spectra.”

Source: National Optical Observatory, Tucson. More at this Keck Observatory page.

← Previous Article Of H.G. Wells, Burt Rutan and the World of Tomorrow
Next Article → Defining the Future of Robotics

0 Comments

Now Reading

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

Recent Posts

On Comments

If you'd like to submit a comment for possible publication on Centauri Dreams, I will be glad to consider it. The primary criterion is that comments contribute meaningfully to the debate. Among other criteria for selection: Comments must be on topic, directly related to the post in question, must use appropriate language, and must not be abusive to others. Civility counts. In addition, a valid email address is required for a comment to be considered. Centauri Dreams is emphatically not a soapbox for political or religious views submitted by individuals or organizations. Human comments only, please -- cut and paste from AI will not be acceptable. A long form of the policy can be viewed on the Administrative page. The short form is this: If your comment is not on topic and respectful to others, I'm probably not going to run it.





Advanced Propulsion Research




Beginning and End







Archives