In the search for yet-undiscovered pulsars or ultra-fast spinning neutron stars, a grand-scale sky survey at the Cornell-managed Arecibo Observatory in Puerto Rico is now taking advantage of the combined processing power of personal computers around the world.

The PALFA Survey, a sky survey using the Arecibo L-band Feed Array (ALFA) -- a system of detectors with seven feeds that enables researchers to image large swaths of sky -- has joined forces with Einstein@Home, an effort based at the University of Wisconsin-Milwaukee (UWM). Einstein@Home involves more than 200,000 people worldwide who donate time on their computers to search for gravitational waves from unknown pulsars.

Using new methods developed at the Albert Einstein Institute (AEI) in Hannover, Germany, Einstein@Home will search for radio pulsars that are part of binary star systems with orbital periods as short as 15 minutes. Conventional searches for radio pulsars lose sensitivity if the pulsars are in orbits shorter than about one hour. But the enormous computational capabilities of the Einstein@Home project -- equivalent to a cluster of more than 50,000 computers -- make it possible to search for pulsars in binary systems with significantly shorter periods.

"Discovery of a pulsar orbiting a neutron star or black hole, with a sub-hour orbital period, would provide tremendous opportunities to test general relativity and to estimate how often such binaries merge," said Jim Cordes, professor of astronomy at Cornell and chair of the Arecibo PALFA Consortium.

Einstein@Home participants will automatically receive work for both the radio and gravitational-wave searches.

"We hope to discover at least a few new radio pulsars per year," said Bruce Allen, director of AEI. "We expect that most of the project's participants will be eager to do both types of searches."

"Combining the sensitivity of the world's largest radio telescope with the distributed computing capabilities of Einstein@Home creates a powerful partnership for discovery," added Dana Lehr, program manager for the Division of Astronomical Sciences at the National Science Foundation (NSF). Cornell's National Astronomy and Ionosphere Center manages Arecibo for the NSF.

All data for PALFA, which began in 2004 and is one of three ongoing sky surveys using the ALFA receiver, are archived and dispensed by the Cornell Center for Advanced Computing.

"The Einstein@Home computing resources are a perfect complement to the data management systems at the Cornell Center for Advanced Computing and the other PALFA institutions," Cordes said.

Gravitational waves were first predicted by Einstein in 1917 as a consequence of his general theory of relativity but have never been directly detected.

Radio pulsars are rapidly spinning neutron stars that emit a lighthouse-like beam of radio waves that sweeps past the Earth as frequently as 600 times per second. Radio pulsars in short-period binary systems are especially interesting because the effects of general relativity can be very strong. The discovery of new pulsars in short-period binaries would also improve estimates of the rates at which binary star systems form and disappear in our galaxy as well as provide new targets to search for gravitational waves.

The large data sets from the survey are archived and processed initially at Cornell and other PALFA institutions. For the Einstein@Home project, data are sent to AEI via high-speed network, preprocessed and then distributed to volunteers around the world. The results are returned to AEI, Cornell and UWM for further investigation.

The Arecibo Observatory is the largest single-aperture radio telescope on the planet and is used for studies of pulsars, galaxies, solar system objects and the Earth's atmosphere.

The NSF supports the work through grants to Einstein@Home; to PALFA; and through a cooperative agreement with Cornell to operate the Arecibo Observatory.