Scientists from the U.S. and Canada reported that they were able to detect signs of permanent gravitational radiation, which passes through the universe and distorts the fabric of space-time. The findings were published in The Astrophysical Journal Letters.
In 2017, scientists conducting an experiment called the Laser Interferometer Gravitational-Wave Observatory (LIGO), won the Nobel Prize in physics for the first-ever direct detection of gravitational waves produced by the merger of two black holes about 1.3 billion light-years from Earth. The waves produced by this collision disturbed the gravitational-wave background of the Universe and reached the Earth.
In addition to such one-time strong disturbances, which astrophysicists have already learned to record, there is the so-called background gravitational wave – a constant stream of gravitational radiation, which, according to theory, is constantly washing over the Earth.
It is this background radiation that scientists from the North American Nanohertz Gravitational-Wave Observatory (NANOGrav) project have tried to detect. For 13 years, they have been studying the light coming from dozens of pulsars scattered throughout our galaxy, using it as a huge space observatory to find hints of a unique gravitational “ripple” in the universe.
“We have detected a strong signal in our data set. We can’t yet say it’s background gravitational waves, but our goal is getting closer,” astrophysicist Joseph Simon, the lead author of the new paper, is quoted as saying in a press release from the University of Colorado at Boulder.
“These early hints of a background of gravitational waves suggest that supermassive black holes are indeed merging and that we are wiggling in a sea of gravitational waves resulting from supermassive black holes merging in galaxies throughout the universe,” said Julie Comerford, associate professor of astrophysics and planetology at the University of Colorado, another study author.
NANOGrav is combined with two other projects from Europe and Australia into a single research network called the International Pulsar Timing Array, which looks for gravitational waves on a continuous basis.
According to the authors, no other observatories are able to detect background gravitational waves because they are focused on looking for one-time events lasting a few seconds.
“We, on the other hand, are looking for waves lasting years or decades,” Simon notes. – According to the theory, galaxy mergers and other cosmological events cause a continuous burst of huge gravitational waves. It takes years or even longer for one such wave to pass by Earth. For this reason, no other existing experiments can detect them directly.”
To capture background gravitational noise, NANOGrav scientists observed pulsars – cosmic sources of flashing pulses, bursts of radio emission whose periodicity remains unchanged – with ground-based telescopes. Pulsars can be compared to galactic beacons constantly in the same place.
Passing gravitational waves alter the steady pattern of light emanating from pulsars by increasing or contracting the relative distances that these beams travel through space. In other words, scientists can theoretically detect the background of gravitational waves by tracking correlated changes in the arrival times of pulsar radiation on Earth.
The goal of the scientists was to observe as many pulsars as possible and for as long as possible. To date, several years of data have been collected on 45 pulsars.
“The ability to detect the background of gravitational waves is huge, but only the first step,” Simon stresses. – Step two is to determine what’s causing these waves and find out what they can tell us about the universe.”
Analysis of the observations has shown that the light emanating from the pulsars is influenced by some common background process. Researchers can’t yet say exactly what causes the signals to shift.