Since scientists first detected gravitational waves from a pair of colliding black holes in 2015, there has been mounting evidence that the universe must be full of them.
Every mass event – every merger of black holes or neutron stars, every supernova – was supposed to send out gravitational waves ringing in spacetime.
The cumulative effect of all these waves would create a faint background hum that permeates the entire universe. This gravitational wave background is predicted to be weak and very difficult to detect. Nevertheless, a year ago, scientists from the international collaboration NanoGRAV said that they may have succeeded.
Now, preliminary new evidence has emerged from the International Pulsar Timing Array (IPTA) consortium that we may have detected a drone. If this is confirmed, it will be a very big deal indeed.
“This is a very exciting signal!” says astrophysicist Xiyuan Chen of the Paris Observatory and CNRS in France.
“While we don’t have definitive evidence yet, we may be starting to detect a background of gravitational waves.”
As we explained last year, the signal comes from the observation of a dead star called a pulsar. These are neutron stars that are oriented in such a way that they emit beams of radio waves from their poles, spinning at a speed of a millisecond, comparable to the speed of a kitchen blender.
These flares are incredibly accurate in timing, which means pulsars are arguably the most useful stars in the universe.
Changes in their time can be used for navigation, for exploring the interstellar medium and studying gravity. Since the discovery of gravitational waves, astronomers have also used them to find them.
This is due to the fact that gravitational waves distort spacetime by passing through them, which should theoretically change – very slightly – the synchronization of radio pulses emitted by pulsars when the spacetime between us and them stretches and contracts.
An individual pulsar has little to tell us, but if these temporal variations are observed across multiple pulsars, it could indicate the presence of gravitational waves. This is called a temporary pulsar array.
The team’s dataset is based on observations of 65-millisecond pulsars, whose timing is consistent with what we expect from a background of gravitational waves.
This is not solid evidence, at least not yet. But this is one step closer to that.
What scientists really need is to see a special signal in the pairs of pulsars, the strength of which depends on their spatial distance in the sky. We haven’t seen this yet because the signal is too weak, but the signal we saw is what we expected to see first.
“The first hint of a gravitational wave background might be a signal similar to that seen in issue 2 of the International Pulsar Synchronization System data,” says astrophysicist Bhal Chandra Joshi of the National Center for Radioastrophysics in India.
“Then, with more data, the signal will become more meaningful and show spatial correlations, at which point we know that it is the background of gravitational waves. We look forward to providing several years of new IPTA data for the first time to help detect the background of gravitational waves. “
Other causes of the signal should also be excluded.
“We are also studying what else this signal might be,” says astrophysicist Boris Goncharov of the Gran Sasso Scientific Institute in Italy.
“For example, perhaps it could be the result of noise present in the data from individual pulsars that could have been incorrectly modeled in our analyzes.”
This means that there is still a lot of scientific research to be done before we can definitively state that the background of gravitational waves has been detected. But with proof in hand, it’s wise to get a little worried.
This is because if we detect a background of gravitational waves, the most likely source is collisions between some of the most massive objects in the universe – supermassive black holes.
This means the signal could help solve mysteries like the latest parsec problem, which suggests supermassive black holes cannot merge, and help us better understand galactic evolution and growth.
“Detecting gravitational waves from massive binary black holes or from another cosmic source will give us unprecedented insights into how galaxies form and grow, or the cosmological processes taking place in the young universe,” says astrophysicist Alberto Vecchio of the University of Moscow. Birmingham in the UK.
“Achieving this requires a major international effort on the scale of the IPTA, and the next few years could bring us a golden age for this exploration of the universe.”
The team’s research was published in Royal Astronomical Society Monthly Notices…