A Star at the Edge of Eternity
A Saturn-size star just 40 light-years away will outlive nearly all of its peers
By Ken Croswell
Every star that now shines will one day die, but some stars live far longer than others. Our 4.6-billion-year-old sun will shrivel into a white dwarf in 7.8 billion years. Now astronomers say a dim red star south of the constellation Orion will outlive any other yet examined. "It actually will live for much longer than the current age of the universe—for literally trillions of years," says Sergio Dieterich, an astronomer at Georgia State University.
Paradoxically, the less mass a star is born with, the longer it lives. Most stars, including the sun, create their energy by using nuclear reactions to convert hydrogen into helium at their centers. Because these stars constitute the vast majority, astronomers call them main-sequence stars. To such a star, mass is both a blessing and a burden. On the one hand, mass provides the fuel that powers the star. On the other hand, the more massive the star, the hotter its center gets, which speeds up the nuclear reactions, making the star shine more brightly and exhaust its fuel more quickly.
The least massive and thus longest-lived main-sequence stars, born with only 8 to 60 percent of the sun's mass, are red dwarfs. Cool, faint and small, red dwarfs outnumber all other stars put together but are so dim that you can't see a single one with the naked eye. The smallest and least massive red dwarfs will live for trillions of years.
There's a limit, though, to how small and long-lived a successful star can be. If an aspiring star arises with too little mass, it becomes not a red dwarf but a failed star known as a brown dwarf. Despite the name, a brown dwarf glows red when young—from both the heat of its birth and nuclear reactions that later dwindle—then fades to black. Because a young brown dwarf looks like a red dwarf, distinguishing the two is often difficult.
more
http://www.scientificamerican.com/article.cfm?id=a-star-at-the-edge-of-eternity