NO FLYING TOASTERS HERE: A screen shot of Einstein@Home, a volunteer computing program that taps idle computer time to scan astrophysical data for gravitational waves and pulsars. Image: EINSTEIN@HOME/B. KNISPEL, ALBERT EINSTEIN INSTITUTE
A newfound stellar remnant some 17,000 light-years away is not your everyday pulsar. For starters, the hyperdense, swiftly pirouetting object appears to belong to a rare class known as disrupted recycled pulsars. Pulsars are so known because they rotate rapidly—this one spins more than 40 times a second—and give off a beam of radio waves that sweeps across the sky, much like a lighthouse. To an outside observer the radiation appears to pulse each time the beam points in the observer's direction.
A disrupted recycled pulsar is a former member of a binary stellar pairing that first exploded as a supernova and collapsed to an extraordinarily dense object known as a neutron star, before cannibalizing matter from its neighbor, spinning faster all the while, and finally breaking free from its binary companion when the neighbor exploded as a supernova itself. Disrupted recycled pulsars are uncommon—a recent study estimated that of more than 1,500 known pulsars, only eight are of the disrupted recycled variety.
That life history surely qualifies as interesting, but the most noteworthy aspect of the newly located pulsar, known as PSR J2007+2722, is the way it was discovered. The celestial rarity was located by the personal computers of individuals in the U.S. and Germany who had lent their idle processor time to Einstein@Home, a campaign that has used hundreds of thousands of volunteered computers to mine astrophysical data sets for interesting phenomena. The discovery was announced in a paper published online in Science August 12.
Volunteer computing entered the limelight in 1999 with the launch of SETI@home, a program that farms out data from radio telescopes to volunteers, whose computers automatically sift through the telescopic signals for possible signs of alien life. (SETI stands for search for extraterrestrial intelligence.) In 2002 the University of California, Berkeley, expanded the volunteer-computing platform with the launch of BOINC (for Berkeley Open Infrastructure for Network Computing), an open-source system that allowed other data-heavy projects to follow the lead of SETI@home. Nowadays there are dozens of projects available through BOINC, including Climateprediction.net, which uses volunteer computers to test climate models; Rosetta@home, which explores three-dimensional protein structures; and Einstein@Home, which started in 2005 as a search for ripples in spacetime known as gravitational waves.
But the direct detection of gravitational waves, which are a fundamental prediction of Albert Einstein's theory of general relativity, appears to be years—and possibly decades—away, as the current generation of gravitational-wave detectors has so far failed to find any. So in 2009 Einstein@Home's minders added a more achievable goal to the program. About one third of the time, the campaign now mines data from the 305-meter Arecibo Observatory in Puerto Rico, the largest single radio telescope on Earth, looking for the signature of pulsars.
"The search for gravitational waves is probably going to take a long time," says Einstein@Home's director Bruce Allen, a physicist at the Max Planck Institute for Gravitational Physics in Hannover, Germany, and the University of Wisconsin–Milwaukee. It would be nice, Allen and his colleagues thought, "if we could look for something that we might find more often." A more attainable target, Allen notes, might also serve as an enticement to keep volunteers engaged in the program.
The first year or so in the pulsar hunt passed without incident. But in June, just a few months after an upgrade to the Einstein@Home code sped the search roughly sevenfold, a pair of volunteer computers snagged the campaign's first pulsar. (All work is done twice for validation, Allen notes.) The discovery came from the PCs of Daniel Gebhardt of the University of Mainz in Germany and of Chris and Helen Colvin of Ames, Iowa.
The Colvins, who both work for Wells Fargo bank—she as a software tester and he as a systems architect—are longtime participants in volunteer computing projects. "We signed up for SETI@home before there was even BOINC," Helen Colvin says.
The pulsar discovery highlights the power of cooperative computing—even a "run-of-the-mill desktop PC," as Chris Colvin describes his home-built machine, can contribute to scientific knowledge. (And moreover, he says, the program makes for a pretty screen saver.)
It is fitting that American and German machines co-discovered PSR J2007+2722, as the U.S. and Germany contribute the most resources to Einstein@Home and to BOINC projects as a whole. But even those contributions come from a tiny fraction of 1 percent of the population, notes Benjamin Knispel, a graduate student in physics at the Max Planck Institute for Gravitational Physics and the lead author of the Science paper. "That means there is huge potential if even 10 times as many people attached their computers," Knispel says.
But volunteer contributions have involved more than just idle processor time. Knispel, who wrote much of the pulsar code for Einstein@Home, says that volunteers have contributed to the programming effort as well, helping to boost the program's speed.
As for the Colvins, they say that they plan to continue contributing their PC downtime to BOINC projects. "There is still plenty more to be discovered," Chris Colvin says. But the couple's computer, despite its newfound status as a pulsar-finder, has now been relegated to a perch in the basement. The Colvins are expecting their first child in a matter of days, and they need the space for a nursery.