Gravitational waves are ripples in space-time that come in many forms. So far, short-duration gravitational wave signals have been observed from colliding black holes and colliding neutron stars, but scientists expect to find other kinds of gravitational waves. Recently published research led by the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)studied continuous waves: long-lasting gravitational waves, in this particular case, waves from neutron stars—old dead stars—in specific star systems called low-mass X-ray binaries. Gravitational-wave detectors LIGO (Laser Interferometer Gravitational-wave Observatory) and Virgo provide excellent data to search for continuous waves as their signals are likely to be present in the detector data all the time (compared to gravitational waves from colliding black holes, which last only a second or so).
Source:
https://phys.org/news/2020-07-gravitational-x-ray-star-systemsthe.html