Gravitational waves were first predicted by Einstein in 1916 as a consequence of his general theory of relativity, but have not yet been directly detected. Einstein@Home was developed as part of the World Year of Physics 2005 activities of the American Physical Society. For the past five years, Einstein@Home has been searching for gravitational waves in data from the U.S. LIGO detectors.
Radio pulsars are rapidly spinning neutron stars that emit lighthouse-like beams of radio waves that can sweep past the Earth as often as 716 times per second. They were discovered in 1967 by Jocelyn Bell and Antony Hewish. (Coincidentally, the first one to be discovered was also in the constellation of Vulpecula.) Pulsars that have orbiting companions are called binary pulsars. They have been used to verify Einstein’s theory of general relativity to very high precision.
Disrupted Recycled Pulsar
When two massive stars are born close together from the same cloud of gas, they can form a binary system and orbit each other from birth. If those two stars are at least a few times as massive as our Sun, their lives will both end in supernova explosions. The more massive star explodes first leaving behind a neutron star. If the explosion does not kick the second star away, the binary system survives. The neutron star can now be visible as a radio pulsar, and slowly loses energy and spins down. Later, the second star can swell up, allowing the neutron star to suck up its matter. The matter falling onto the neutron star spins it up and reduces its magnetic field. This is called "recycling" because it returns the neutron star to a quickly-spinning state. Finally, the second star also explodes in a supernova, producing another neutron star. If this second explosion also fails to disrupt the binary, a double neutron star binary is formed. Otherwise, the spun-up neutron star is left with no companion and becomes a "disrupted recycled pulsar", spinning between a few and 50 times per second.
Arecibo Observatory is the largest single-dish radio telescope on the planet and is used for studies of pulsars, galaxies, solar system objects, and the Earth's atmosphere. The first binary pulsar was discovered at Arecibo in 1974 and led to Hulse and Taylor's 1993 Nobel Prize in Physics, because of its stringent test of general relativity. The Pulsar ALFA (PALFA) survey now being conducted at Arecibo uses a specialized radio camera, the Arecibo L-band Feed Array, and is conducted by the PALFA Consortium of astronomers. The large data sets from the Arecibo survey are archived and processed initially at Cornell and other PALFA institutions. For the Einstein@Home project, data are sent from the Cornell Center for Advanced Computing to the Albert Einstein Institute in Hannover via high-bandwidth Internet links, pre-processed and then distributed to computers around the world. The results are returned to AEI and Cornell for further investigation.
The Pulsar ALFA (PALFA) Consortium was formed in 2003 to conduct a large scale pulsar survey with the Arecibo telescope. It includes astronomers at twenty universities, institutes and observatories worldwide.
The Max Planck Institute for Gravitational Physics (Albert Einstein Institute) is the largest research institute in the world devoted to the study of general relativity. Its two branches in Potsdam and Hannover support research in astrophysics, theoretical physics, mathematics, and experimental physics. The AEI Hannover is a joint undertaking of the Max Planck Society and the Leibniz Universität Hannover. Together with British partners it operates the GEO600 gravitational wave detector near Hannover, Germany, is a partner in the American LIGO project, and plays a major role in the analysis of the data from all existing gravitational wave detectors, including the VIRGO detector in Italy. The software that is used in the Einstein@Home radio searches was developed by the AEI in Hannover.
The Center for Gravitation and Cosmology at the University of Wisconsin–Milwaukee hosts the Einstein@Home project and plays a major role in the data analysis activities of the LIGO Scientific Collaboration. It also carries out Arecibo radio observations as an Arecibo Remote Control Center (ARCC).
BOINC is the Berkeley Open Infrastructure for Network Computing used by Einstein@Home and many other volunteer computing projects like SETI@Home. It was developed at the University of California at Berkeley's Space Sciences Laboratory, in an effort led by Dr. David Anderson.
The U.S. National Science Foundation supports this work through grants to the Einstein@Home project, to the PALFA project, to the BOINC project at the University of California, Berkeley, and through a cooperative agreement with Cornell University to operate the Arecibo Observatory. The Albert Einstein Institute for Gravitational Physics is supported by the Max Planck Society and the Leibniz Universität Hannover.