by Researchers have announced that they have created the current best map of the gravitational wave background in the universe. They did this using the incredible MeerKAT radio telescopes in South Africa. But this map has an unexpected feature: there is a possible anomaly in the gravitational waves flowing through our Milky Way, linked to the merger of two black holes.
Any moving object with mass creates gravitational waves – even moving your hand does that. These are of course too weak to be detected. The motion of planets, stars and even supermassive black holes are also far too faint to be detected directly, but they all contribute to the gravitational wave background. We’re getting closer to consistent detections of this sloshing of space-time throughout the universe, but it hasn’t been easy. We had to use a detector that covers a large part of our own galaxy, the Milky Way.
“By studying the background we can tune in to the echoes of cosmic events over billions of years,” Dr. Matt Miles, a researcher at OzGrav and lead author of two of the new studies, said in a statement. “It reveals how galaxies, and the universe itself, have evolved over time.”
The gravitational wave background is passing through us as we speak.
Image credit: Carl Knox, OzGrav, Swinburne University of Technology
A detector the size of a galaxy may seem surprising. How can we have an observatory in the entire Milky Way when the farthest man-made object (Voyager 1) is still less than one light-day away from Earth? The answer is that we use a phenomenal cosmic object to our advantage: pulsars.
Pulsars are a type of neutron star, the end product of certain supernovae. A subclass of pulsars, called millisecond pulsars, rotate hundreds of times per second and pulsate from our vantage point. Their rotation is so regular that they can be as accurate as atomic clocks on Earth. Changes in this pulsation – as we see them – therefore imply that a gravitational wave has passed through it. You need many measurements from each pulsar and from many pulsars to convert those signals into an actual detection of the background. This approach is called the Pulsar Timing Array.
The MeerKAT Pulsar Timing Array is the latest in an international effort to determine the background of gravitational waves, and the researchers claim their measurement is stronger than other studies conducted to date – and that they do it only a third of the time could do. the time. The map is highly detailed thanks to new approaches, which led to the discovery of a possible directional deviation related to supermassive black holes.
“What we see indicates a much more dynamic and active universe than we expected,” added Dr Miles, from Swinburne University of Technology. “We know that supermassive black holes are merging, but now we’re starting to wonder: where are they, and how many are out there?”
The idea was that the gravitational wave background is uniform; there are supermassive black holes that merge in so many different directions and distances that overall they form a consistent slosh. But if these findings are correct, we may have a preferential source influencing our Galaxy.
“The presence of a hotspot could indicate a clear source of gravitational waves, such as a pair of black holes billions of times the mass of our Sun,” said lead author of the third study, Rowina Nathan, from OzGrav and Monash University. The layout and patterns of gravitational waves show us how our universe exists today and contains signals dating back to the Big Bang. There is still more work to be done to determine the significance of the hotspot we have found, but this is an exciting step forward for our field.”
More observations will be needed to verify and improve this data set, and past announcements regarding the gravitational wave background have been more cautious. Seeing the confidence increase is exciting, but it’s a young field, so we’ll see how different observations shape the full results.
“In the future, we want to understand the origin of the gravitational wave signal coming from our datasets. By looking for variations in the gravitational waves in the sky, we are looking for the fingerprints of the underlying astrophysical processes,” said Kathrin Grunthal, researcher at the Max Planck Institute for Radio Astronomy and co-author of one of the studies. .
The three papers with these results were published in the Monthly Notices of the Royal Astronomical Society and can be read here, here and here.
