Over 13 years, a consortium of astronomers has been monitoring the signals from rotating stars in hopes of capturing narrow waves in space, known as gravitational waves.
Finally, they may have discovered the first low-frequency gravity waves ever discovered.
The news came from a team of researchers from the North American Nanohertz Observatory for Gravity Waves (NANOGrav), who say they have found a weak signal that could be caused by low-frequency gravity waves, first of its kind. Surprisingly, this data comes from the now obsolete Arecibo Observatory.
The new finding is outlined in a study published in the January issue of The Astrophysical Journal, and it has a huge impact on how we look – or rather, listen to the universe.
Here is the background – On September 15, 2015, scientists first discovered a signal from gravitational waves. The sign was the star that came as a result of a merger between two black holes that hit 1.3 billion years ago.
Gravity waves are caused by accelerated masses of cosmic creatures, which emit waves at the speed of light. If electromagnetic radiation, or light, is a way for astronomers to see the universe, gravitational waves are a way to listen in to the universe.
Using the Gravitational-Wave Observatory (LIGO) Laser Interferometer detectors and the Virgo detector, scientists are able to detect the signals created by these waves.
By the time they reach Earth, the gravitational waves are relatively weak and last only a few seconds. Scientists study the signals and trace the origin of the waves of gravity, listening into the early events of the universe.
Most of these incidents that caught the detectors are caused by hitting two black holes.
Low frequency gravity waves different. They are formed over billions of years by large numbers of black holes orbiting each other, producing signals with much longer waves.
Compared to their high-frequency counterparts, low-frequency gravity waves provide more stable background noise.
As a result, they have to find years of data.
How they did it – NANOGrav is made up of more than 100 astronauts from across the United States and Canada united by the same quest to detect low frequency gravitational waves.
The astronomers used a type of star called a pulsar to find them. Pulsars are dense stars with a strong magnetic field, and they rotate while emitting a charge of electromagnetic radiation. Because of their unique properties, scientists often use pulsars as cosmic lighthouses. ‘
Pulsar stars are known as the timekeepers of the universe, emitting light at a constant time. Thus, any irregularities at that time could have been caused by gravitational waves stretching and declining space-time, according to the study.
The ripples caused by gravity waves cause small movements in the time expected for the pulsar signal to reach the Earth, indicating that the Earth’s position has shifted.
The researchers saw a group of pulsars using the Arecibo Observatory in Puerto Rico, which collapsed in December 2020, complete its rule as one of the largest radio telescopes in the world.
They measured the time of the signals that the particles were scattering across the sky at the same time, a method known as the “pulsar time series,” and were able to detect minute changes in the Earth’s position from the stars.
Don’t search – This is still the strongest signal of a low frequency gravity wave. The scientists have not yet been able to prove that the minute changes are due to a low frequency gravity wave signal. But they did not rule out other possibilities for these changes, such as a ban from another issue in the Solar System.
“It is interesting to see such a strong signal emerge from the data,” Joseph Simon, a member of NANOGrav and the study ‘s lead researcher, said in a statement.
“However, because the gravitational wave signal we are looking for spans our entire view, we need to understand our sound carefully,” he said.
“We can strongly rule out some known sound sources, but we still can’t say if the signal is actually from gravitational waves. For that, we need more data,” he says.
What Now – This discovery took years in the making, but it may take a few more years for the scientists at NANOGrav to prove that low-frequency gravitational waves caused the shift in the Earth’s position from the pulsar signal.
To do that, the researchers need to expand the database, add more pulsar stars and look for even longer periods.
At the same time, they also need to rule out other possible reasons for the space-time disorder. The team at NANOGrav is performing computer simulations to determine if the detected sound was caused by something other than gravitational waves.
“Trying to detect gravitational waves with a pulsar time series must be patient,” Scott Ransom, a researcher at the National Radio Astronomy Observatory and current chairman of NANOGrav, said in a statement.
“We’re currently analyzing more than a dozen years of data, but definitive discovery is likely to give a couple more. It’s good that these new results are exactly what we’d expect to see as we climb closer to find. “
Whether or not this discovery is confirmed as the first low-frequency gravitational wave, scientists are certainly keeping an ear closer to the cosmos.
Summary: We find the background of an isotropic stochastic wave (GWB) in the 12.5 yr amplitude data set collected by the North American Nanohertz Observatory for Gravitational Waves. Our analysis finds strong evidence of a stochastic process, modeled as a law of power, with common amplitude and spectral slope over pulsars. Under our fiducial model, the Bayesian posterior of the amplitude is for f−2/3 the power-law spectrum has a median of 1.92, expressed as the normal GW species × 10−15 and 5% –95% sizes 1.37–2.67 × 10−15 at a Bayes factor reference frequency favorable to the common spectrum process versus independent red noise processes in each pulsar greater than 10,000. However, we do not find statistically significant evidence that this process has quadratic space correlations, which we would think would be necessary to apply GWB detection according to general relevance. We find that the process has no monopolar or dipolar correlations, which may come from, for example, a reference clock or systematics ephemeris solar system, respectively. The posterior amplitude is significantly supported above previously reported high levels; we explain this in terms of the Bayesian primates being adopted for pulsar red sound. We study the potential effects to the binary population of black hole under the assumption that the signal is indeed astrophysical in nature.