Continuous-Wave Group

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).

Observational results to date

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

Meetings with Neutron Star Astronomers

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.

Other links of interest:

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.