LIGO Scientific Collaboration and Virgo Collaboration
Public Web Pages
The LSC-Virgo Continuous-wave ("Pulsar") Working Group searches for continuous-wave gravitational radiation in data from the LIGO, Virgo, and GEO 600 gravitational wave detectors. The most likely sources of such radiation are rotating neutron stars in our Galaxy. A small bump on the star's surface (~mm high or less) or a slight wobble in its rotation could generate gravitational disturbances that would be detectable as waves here on Earth.
We carry out searches for radiation both from known pulsars (neutron stars that regularly beam electromagnetic radiation toward the Earth) and from as-yet-undiscovered neutron stars. In searching for continuous-wave sources, one must make corrections for the Earth's rotation and orbital motion around the Sun. These corrections depend on the precise location of an assumed source and become increasingly important as the time of observation increases. An all-sky search for sources spinning at detectable frequencies, if carried out at the intrinsic sensitivity of the interferometers, would exhaust the capability of all computers in existence!
As a result, one must make tradeoffs in sensitivity (or distance at which a source of given luminosity can be seen) in order to cover a large parameter space (sky location, frequency, frequency spindown). A variety of search methods have been developed that make different choices for those tradeoffs in searches carried out in the first six LIGO science runs (S1-S6) and first four Virgo science runs (VSR1-VSR4) to date. More information can be found in the publications linked below.
The most ambitious search we carry out is called Einstein@Home, one of the world's largest distributed-computing projects, modeled on and supported by the pioneering Seti@Home project. The Einstein@Home project allows any interested person to help search for unknown neutron stars by downloading a program that runs in background on a personal computer when the computer is otherwise idle. Einstein@Home has an eye-catching screen saver that shows a rotating celestial sphere, with the pulsars in the Milky Way marked in color. Although Einstein@Home has not yet found gravitational waves from a neutron star, it has discovered a new milli-second radio pulsar (PSR J2007+2722) in radio data from the Arecibo Observatory.
An especially notable result to date is a limit on the strength of gravitational radiation emitted by the Crab Pulsar, a young neutron star (created in a supernova reported by Chinese astronomers in 1045 A.D.) with a radius of only ~10 km, but more massive than the Sun, and spinning on its axis 30 times per second! The Crab's rotation frequency is decreasing perceptibly, implying a significant energy loss. Our most recent limits indicate that no more than one percent of that energy loss can be attributed to gravitational wave emission.
We are wrapping up searches in the data from the most sensitive of the initial LIGO and Virgo science runs (LIGO S5-6, Virgo VSR2-4) as we start looking at data from the first Advanced LIGO Observing run O1 (fall 2015).
Known neutron stars
|Setting upper limits on the strength of periodic gravitational waves from PSR J1939+2134 using the first science data from the GEO 600 and LIGO detectors.||Phys. Rev. D 69 (2004) 082004||gr-qc/0308050|
|Limits on gravitational wave emission from selected pulsars using LIGO data.||Phys. Rev. Lett. 94 (2005) 181103||gr-qc/0410007|
|Upper Limits on Gravitational Wave Emission from 78 Radio Pulsars.||Phys. Rev. D 76 (2007) 042001||gr-qc/0702039|
|Beating the spin-down limit on gravitational wave emission from the Crab pulsar||Astrophys. J. Lett 683 (2008) 45||arXiv:0805.4758|
|Searches for gravitational waves from known pulsars with S5 LIGO data||Astrophys. J. 713 (2010) 671||arXiv:0909.3583|
|First search for gravitational waves from the youngest known neutron star||Astrophys. J. 722 (2010) 1504||arXiv:1006.2535|
|Beating the spin-down limit on gravitational wave emission from the Vela pulsar||Astrophys. J. 737 (2011) 93||arXiv:1104.2712|
|Gravitational-waves from known pulsars: results from the initial detector era||Astrophys. J. 785 (2014) 119||arXiv:1309.4027|
|Narrow-band search of continuous gravitational-wave signals from Crab and Vela pulsars in Virgo VSR4 data||Phys. Rev. D 91 (2015) 022004||arXiv:1410.8310|
|A directed search for gravitational waves from Scorpius X-1 with initial LIGO||Phys. Rev. D 91 (2015) 062008||arXiv:1412.0605|
|Searches for continuous gravitational waves from nine young supernova remnants||Astrophys. J. 813 (2015) 39||arXiv:1412.5942|
Unknown possible sources
|First all-sky upper limits from LIGO on the strength of periodic gravitational waves using the Hough transform.||Phys. Rev. D 72 (2005) 102004||gr-qc/0508065|
|Coherent searches for periodic gravitational waves from unknown isolated sources and Scorpius X-1: results from the second LIGO science run.||Phys. Rev. D 76 (2007) 082001||gr-qc/0605028|
|All-sky search for periodic gravitational waves in LIGO S4 data||Phys. Rev. D 77 (2008) 022001||arXiv:0708.3818|
|The Einstein@Home search for periodic gravitational waves in LIGO S4 data||Phys. Rev. D 79 (2009) 022001||arXiv:0804.1747|
|All-sky LIGO Search for Periodic Gravitational Waves in the Early S5 Data||Phys. Rev. Lett.102 (2009) 111102||arXiv:0810.0283|
|Einstein@Home search for periodic gravitational waves in early S5 LIGO data||Phys. Rev. D 80 (2009) 042003||arXiv:0905.1705|
|All-sky Search for Periodic Gravitational Waves in the Full S5 LIGO Data||Phys. Rev. D 85 (2012) 022001||arXiv:1110.0208|
|Einstein@Home all-sky search for periodic gravitational waves in LIGO S5 data||Phys. Rev. D 87 (2013) 042001||arXiv:1207.7176|
|A directed search for continuous Gravitational Waves from the Galactic Center||Phys. Rev. D 88 (2013) 102002||arXiv:1309.6221|
|Application of a Hough search for continuous gravitational waves on data from the 5th LIGO science run||Class. Quant. Grav. 31 (2014) 085014||arXiv:1311.2409|
|Implementation of an F-statistic all-sky search for continuous gravitational waves in Virgo VSR1 data||Class. Quant. Grav.31 (2014) 165014||arXiv:1402.4974|
|First all-sky search for continuous gravitational waves from unknown sources in binary systems||Phys. Rev. D 90 (2014) 062010||arXiv:1405.7904|
|A search of the Orion spur for continuous gravitational waves using a "loosely coherent" algorithm on data from LIGO interferometers||Phys. Rev. D 93 (2016) 042006||arXiv:1510.03474|
|First low frequency all-sky search for continuous gravitational wave signals||Phys. Rev. D 93 (2016) 042007||arXiv:1510.03621|
|Comprehensive All-sky Search for Periodic Gravitational Waves in the Sixth Science Run LIGO Data||To appear in Physical Review D||arXiv:1605.03233|
|Results of the deepest all-sky survey for continuous gravitational waves on LIGO S6 data running on the Einstein@Home volunteer distributed computing project||To appear in Physical Review D||arXiv:1606.09619|
|Search for continuous gravitational waves from neutron stars in globular cluster NGC 6544||Submitted for publication||arXiv:1607.02216|
We have hosted a series of meetings with neutron star experts since October 2006, in order to ensure that the tradeoffs we make in our computationally limited searches are guided by the latest observational results and theoretical findings. These meetings have proven useful, with the most recent held in Boston in May 2011. Astronomers with an interest in gravitational wave emission from neutron stars are strongly encouraged to attend. Below are the web sites for the meetings in this series.
In addition, a workshop devoted to Probing Neutron Stars with Gravitational Waves was held at Penn State University in June 2009.
Working group chairs: Keith Riles (LSC), Alicia Sintes (LSC), Andrzej Krolak (Virgo)
Astronomy liaison: Ben Owen
This web site is supported by the National Science Foundation.