The EPTA (European Pulsar Timing Array) consortium, which brings together astronomers from European countries, announced the discovery of a new type of gravitational waves: these are ultra-low-frequency gravitational waves, which are supposed to be emitted by systems of supermassive binary black holes weighing from millions to billions of solar masses, located in the centers emerging galaxies. Such gravitational waves can have frequencies on the order of nanohertz and are inaccessible to observation by existing gravitational wave detectors.
European astronomers made the discovery in collaboration with colleagues from Japan and India, studying pulsar observations at six of the world's most sensitive radio telescopes in the UK, Germany, the Netherlands, Italy and France over a period of 25 years.
Gravitational waves are "ripples" on the "fabric" of space-time. Our universe is flat , but massive objects bend space-time around them. If they make a periodic motion, then the gravitational curvature of space-time takes on the character of a wave. Such space-propagating deviations from flat space-time are called gravitational waves; they travel at the speed of light.
When a gravitational wave arrives, it causes all objects to increase or decrease in length a little. In this case, an increase or decrease in the length occurs in directions perpendicular to the direction of wave arrival. Observation of gravitational waves is carried out on installations, which, due to the use of interferometric methods, make it possible to very accurately and quickly measure the change in the length of the detector. Thus, in 2015, gravitational waves were experimentally discovered , which were generated by the merger of black holes; the frequency of the recorded waves ranged from tens to hundreds of hertz.
Gravitational waves can be detected by observing pulsars. These are neutron stars with a magnetic field that rotate at a very high angular velocity (up to 700 revolutions per second) and emit radio emission from their magnetic poles. Due to this, they play the role of cosmic "beacons": they are visible to the earth observer as very regular periodic bursts of radio emission. Their oscillation period is kept with very high accuracy, so they can play the role of a cosmic "clock". The period of their "ticking" can change due to the arrival of low-frequency gravitational waves.
In their work, EPTA astronomers used 25 pulsars in our galaxy as time references. This made it possible to "assemble" from pulsars a "detector" of gravitational waves the size of a galaxy.
Observing gravitational waves from supermassive black hole binaries will provide a "window" for scientists to the early universe and could help understand phenomena such as galaxy mergers.