LIGO Scientific Collaboration logo

Public Webpage of the Continuous Wave Group

LIGO Scientific Collaboration and Virgo Collaboration

Virgo Collaboration logo

What are Continuous Gravitational Waves?

Gravitational waves have been detected by the LIGO (Laser Interferometer Gravitational-wave Observatory) and Virgo gravitational wave detectors. The gravitational wave events detected thus far have been from the collision and merger of two black holes (e.g. GW150914), or two neutron stars (e.g. GW170817). The detectable signatures of events of this type are typically very short, lasting from much less than a second to a few minutes.

Continuous gravitational waves are a different, hypothesised class of gravitational waves which have so far not been detected. Unlike the short-lived chirp events from binary black holes and binary neutron stars, continuous gravitational waves are expected to be always present, like a background humming sound, in the LIGO and Virgo detectors.

The most likely sources of continuous gravitational waves are spinning neutron stars in our Galaxy. A small bump on the star's surface a few millimetres in height, or a slight wobble in its rotation, could generate gravitational disturbances that would be detectable as gravitational waves here on Earth. These waves would, however, be much weaker than those generated by binary black hole or binary neutron star collisions, which makes them much more challenging to detect.

The youngest neutron stars which could be radiating continuous gravitational waves are likely to be hundreds of years old, if not much older. However, it is also possible that a very young neutron star — born in the collision and merger of two neutron stars — may also radiate continuous gravitational waves for a short period of time.

The Continuous Wave Group

The Continuous Wave Group is a joint working group of the LIGO Scientific Collaboration (LSC) and Virgo Collaboration, and is tasked with searching for the signatures of continuous gravitational waves in data from the LIGO and Virgo detectors. We carry out searches for continuous gravitational waves targeted at known astronomical objects: pulsars such as the Crab pulsar, low-mass X-ray binaries such as Scorpius X-1, and supernova remnants such as Cassiopeia A. We also perform all-sky surveys for as-yet unknown sources, e.g. spinning neutron stars in our Galaxy which radiate continuous gravitational waves but are not visible in the electromagnetic spectrum.

In searching for continuous gravitational wave sources, we must make corrections for the intrinsic change in the frequency of the waves over time, the Earth's rotation and orbital motion around the Sun, and in some cases the motion of the source itself if it is in orbit around a companion star. As the timespan of the data being analysed increases, these corrections become very computationally challenging to perform when all or some of the parameters of the source (e.g. its sky position and intrinsic frequency) are not known a priori. For example, an all-sky survey for sources spinning at detectable frequencies, if carried out using the most sensitive search algorithm, would easily exhaust the capability of all computers in existence! For these kinds of searches, we must therefore make use of different algorithms which are not the most sensitive, but are computationally cheap enough to run on modern supercomputers. More information can be found in the publications linked below.


Scientific Publications

This table lists all scientific publications produced (to date) by the Continuous Wave Group and authored by the LSC and/or Virgo Collaborations. See this page for a list of all scientific publications of the LSC-Virgo Collaboration.

Target Source(s) Title, link to Science Summary where available Journal Article Preprint
Searches of data from LIGO/Virgo observing run O2
All-sky survey for unknown sources All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO O2 data 1903.01901
33 pulsars, using relaxed ephemerides Narrow-band search for gravitational waves from known pulsars using the second LIGO observing run 1902.08442
222 pulsars Searches for Gravitational Waves from Known Pulsars at Two Harmonics in 2015-2017 LIGO Data 1902.08507
Searches of data from LIGO/Virgo observing run O1
15 supernova remnants and Fomalhaut b Searches for Continuous Gravitational Waves from Fifteen Supernova Remnants and Fomalhaut b with Advanced LIGO 1812.11656
Long-lived neutron star remnant of GW170817 Search for gravitational waves from a long-lived remnant of the binary neutron star merger GW170817 1810.02581
All-sky survey for unknown sources Full Band All-sky Search for Periodic Gravitational Waves in the O1 LIGO Data Phys. Rev. D 97, 102003 (2018) 1802.05241
11 pulsars, using relaxed ephemerides First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data Phys. Rev. D 96, 122006 (2017) 1710.02327
200 pulsars, sensitive to nontensorial modes First search for nontensorial gravitational waves from known pulsars Phys. Rev. Lett. 120, 031104 (2018) 1709.09203
All-sky survey for unknown sources All-sky Search for Periodic Gravitational Waves in the O1 LIGO Data Phys. Rev. D 96, 062002 (2017) 1707.02667
All-sky survey for unknown sources First low-frequency Einstein@Home all-sky search for continuous gravitational waves in Advanced LIGO data Phys. Rev. D 96, 122004 (2017) 1707.02669
Low-mass X-ray binary Scorpius X-1 Upper limits on gravitational waves from Scorpius X-1 from a model-based cross-correlation search in Advanced LIGO data Astrophys. J. 847, 47 (2017) 1706.03119
Low-mass X-ray binary Scorpius X-1 Search for gravitational waves from Scorpius X-1 in the first Advanced LIGO observing run with a hidden Markov model Phys. Rev. D 95, 122003 (2017) 1704.03719
200 pulsars First search for gravitational waves from known pulsars with Advanced LIGO Astrophys. J. 839, 12 (2017) 1701.07709
Searches of data from LIGO science run S6 and Virgo science runs VSR2VSR4
Globular cluster NGC 6544 Search for continuous gravitational waves from neutron stars in globular cluster NGC 6544 Phys. Rev. D 95, 082005 (2017) 1607.02216
All-sky survey for unknown sources Results of the deepest all-sky survey for continuous gravitational waves on LIGO S6 data running on the Einstein@Home volunteer distributed computing project Phys. Rev. D 94, 102002 (2016) 1606.09619
All-sky survey for unknown sources Comprehensive All-sky search for periodic gravitational waves in the sixth science run LIGO data Phys. Rev. D 94, 042002 (2016) 1605.03233
Direction of Orion spur Search of the Orion spur for continuous gravitational waves using a loosely coherent algorithm on data from LIGO interferometers Phys. Rev. D 93, 042006 (2016) 1510.03474
All-sky survey for unknown sources First low frequency all-sky search for continuous gravitational wave signals Phys. Rev. D 93, 042007 (2016) 1510.03621
9 supernova remnants Searches for continuous gravitational waves from nine young supernova remnants Astrophys. J. 813, 39 (2015) 1412.5942
Crab & Vela pulsars, using relaxed ephemerides Narrow-band search of continuous gravitational-wave signals from Crab and Vela pulsars in Virgo VSR4 data Phys. Rev. D 91, 022004 (2015) 1410.8310
All-sky survey for unknown sources in binary systems First all-sky search for continuous gravitational waves from unknown sources in binary systems Phys. Rev. D 90, 062010 (2014) 1405.7904
195 pulsars Gravitational waves from known pulsars: results from the initial detector era Astrophys. J. 785, 119 (2014) 1309.4027
Searches of data from LIGO science run S5 and Virgo science runs VSR1VSR2
Low-mass X-ray binary Scorpius X-1 Directed search for gravitational waves from Scorpius X-1 with initial LIGO data Phys. Rev. D 91, 062008 (2015) 1412.0605
All-sky survey for unknown sources Implementation of an F-statistic all-sky search for continuous gravitational waves in Virgo VSR1 data Class. Quant. Grav. 31, 165014 (2014) 1402.4974
All-sky survey for unknown sources Application of a Hough search for continuous gravitational waves on data from the fifth LIGO science run Class. Quant. Grav. 31, 085014 (2014) 1311.2409
Direction of Galactic Center Directed Search for Continuous Gravitational Waves from the Galactic Center Phys. Rev. D 88, 102002 (2013) 1309.6221
All-sky survey for unknown sources Einstein@Home All-sky Search for Periodic Gravitational Waves in LIGO S5 Data Phys. Rev. D 87, 042001 (2013) 1207.7176
All-sky survey for unknown sources All-sky Search for Periodic Gravitational Waves in the Full S5 LIGO Data Phys. Rev. D 85, 022001 (2012) 1110.0208
Vela pulsar Beating the spin-down limit on gravitational wave emission from the Vela pulsar Astrophys. J. 737, 93 (2011) 1104.2712
Supernova remnant Cassiopeia A First Search for Gravitational Waves from the Youngest Known Neutron Star Astrophys. J. 722, 1504 (2010) 1006.2535
116 pulsars Searches for Gravitational Waves from Known Pulsars with Science Run 5 LIGO Data Astrophys. J. 713, 671 (2010) 0909.3583
All-sky survey for unknown sources Einstein@Home search for periodic gravitational waves in early S5 LIGO data Phys. Rev. D 80, 042003 (2009) 0905.1705
All-sky survey for unknown sources All-sky LIGO Search for Periodic Gravitational Waves in the Early S5 Data Phys. Rev. Lett. 102, 111102 (2009) 0810.0283
Crab pulsar Beating the Spin-Down Limit on Gravitational Wave Emission from the Crab Pulsar Astrophys. J. Lett. 683, L45 (2008) 0805.4758
Searches of data from LIGO science runs S1S4
All-sky survey for unknown sources Einstein@Home Search for Periodic Gravitational Waves in LIGO S4 Data Phys. Rev. D 79, 022001 (2009) 0804.1747
All-sky survey for unknown sources All-sky Search for Periodic Gravitational Waves in LIGO S4 Data Phys. Rev. D 77, 022001 (2008) 0708.3818
78 pulsars Upper Limits on Gravitational Wave Emission from 78 Radio Pulsars Phys. Rev. D 76, 042001 (2007) gr‑qc/0702039
Low-mass X-ray binary Scorpius X-1 Searches for periodic gravitational waves from unknown isolated sources and Scorpius X-1: Results from the second LIGO science run Phys. Rev. D 76, 082001 (2007) gr‑qc/0605028
All-sky survey for unknown sources First all-sky upper limits from LIGO on the strength of periodic gravitational waves using the Hough transform Phys. Rev. D 72, 102004 (2005) gr‑qc/0508065
28 pulsars Limits on gravitational wave emission from selected pulsars using LIGO data Phys. Rev. Lett. 94, 181103 (2005) gr‑qc/0410007
Pulsar PSR J1939+2134 Setting upper limits on the strength of periodic gravitational waves using the first science data from the GEO600 and LIGO detectors Phys. Rev. D 69, 082004 (2004) gr‑qc/0308050

Workshops

This is a list of workshops with a focus on the science of continuous gravitational waves. Several of these workshops were organised by the Continuous Wave Group to provide a forum for discussion with neutron star experts, in order to ensure that our searches are guided by the latest observational results and theoretical findings. Other workshops were independently organised with the involvement of Continuous Wave Group members.


Contacts

Enquries should be directed to the co-chairs of the Continuous Wave Group: Evan Goetz (LSC), Paola Leaci (Virgo), and Karl Wette (LSC).


Acknowledgements

The LIGO observatories are built and operated by the LIGO Laboratory (California Institute of Technology and Massachusetts Institute of Technology) with participation by the LIGO Scientific Collaboration, and are supported by the U.S. National Science Foundation.

The Virgo detector is designed, built and operated by a collaboration that includes the Centre National de la Recherche Scientifique (France), the Istituto Nazionale di Fisica Nucleare (Italy) and Nikhef (Netherlands), with Polish, Hungarian and Spanish institutes and the European Gravitational Observatory (EGO) consortium.

For general information, visit ligo.org and virgo-gw.eu.


This page was last modified on .