- News Home
5 December 2013 11:26 am ,
Vol. 342 ,
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
- 5 December 2013 11:26 am , Vol. 342 , #6163
- About Us
How Many Stars Never Make the Big Time?
24 May 2012 4:05 pm
Becoming a star can be a challenge. But new observations reveal that it's much easier in space than in Hollywood. Only about 14% of all aspiring celestial stars fizzle out, researchers report.
In principle, it's easy to deduce how many stars succeed: just compare the numbers of normal stars with the number of failed stars, also known as brown dwarfs. These flops are born with less than 8% of the sun's mass, so their centers never heat up enough to sustain the nuclear fusion of hydrogen-1, the isotope that powers so-called main-sequence stars like the sun. Most brown dwarfs do burn hydrogen-2, or deuterium, but it soon runs out, and all nuclear reactions cease. When young, a brown dwarf glows red—chiefly from the heat of its birth—and then cools and fades as it ages. That makes them hard to find—and thus hard to know whether they're rare or as plentiful as full-fledged stars.
Astronomer J. Davy Kirkpatrick of the California Institute of Technology in Pasadena and colleagues decided to take a look at infrared wavelengths, where the objects emit most of their radiation. The team used NASA's Wide-field Infrared Survey Explorer (WISE) spacecraft, launched in late 2009, to detect brown dwarfs near the sun, some of which have cooled to room temperature. WISE spotted 16 previously unknown brown dwarfs within 26 light-years of Earth. As the astronomers will report in the 10 July issue of The Astrophysical Journal, comparing the number of brown dwarfs with the number of full-fledged stars suggests that the solar neighborhood has one failed star for every six success stories.
"It was surprising to me," says Kirkpatrick, who had expected to find far more brown dwarfs. If they were more common, one might reside even closer than Alpha Centauri, the nearest star system to the sun. "It's a lot less likely we're going to find any brown dwarf that's that close." The two nearest known brown dwarfs orbit Epsilon Indi, a star 11.8 light-years away, which is nearly three times farther from Earth than Alpha Centauri.
Astronomer Aleks Scholz of the Dublin Institute for Advanced Studies says the new estimate for the number of brown dwarfs agrees with his team's result from a very different approach: searching star clusters so young their brown dwarfs haven't had time to fade, making them easier to spot. He and other astronomers have found an approximately 1:5 ratio between brown dwarfs and normal stars.
However, astronomer Todd Henry of Georgia State University in Atlanta is critical of the new work's conclusion. "I think it's premature," says Henry, who suspects that many of the brown dwarfs WISE has found are farther away from Earth than claimed. That would mean they are less abundant than the researchers estimated, and Henry says the ratio of brown dwarfs to normal stars could be anywhere between 1:5 and 1:20.