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Gravitational wave interferometers such as LIGO are deeply impressive feats of engineering, perfected over the years to measure barely detectable ripples in spacetime generated by massive cosmic objects.
But the cosmos gave us another tool with which we might be able to detect elusive gravitational wave signals. It’s a type of dead star called pulsars, and the delays in their precisely synchronized flashes could be a clue to the background of the Universe’s gravitational waves – the hum of billions of years ago. cosmic collisions and star explosions.
Earlier this year, the NANOGrav collaboration announced that it may have detected this buzz. Now a second group, led by astrophysicists Boris Goncharov and Ryan Shannon of the ARC Center of Excellence for the Discovery of Gravitational Waves (OzGrav) in Australia, have revealed their own findings.
Although their conclusions are more conservative, the results are not inconsistent with the background noise of gravitational waves. This suggests that we may be barking the right tree after all – but there is still a lot of work to be done before a conclusive claim can be made.
“Recently, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration found evidence for the common spectrum component in their 12.5-year data set,” the researchers wrote in their paper. .
“Here we report a background research using the second version of the data from the Parkes Pulsar synchronization network. If we are forced to choose between the two NANOGrav models – one with a common spectrum process and the other without – we find strong support for the common spectrum process. “
Gravitational wave astronomy is still in its infancy. We have detected gravitational waves using LIGO-Virgo interferometers here on Earth – the huge blips generated by the collision of black holes and neutron stars. But there should be a much weaker signal permeating the Universe – the background of gravitational waves.
It is the collective signal accumulated throughout the history of the Universe. Every pair of colliding black holes or neutron stars, every core-collapsing supernova – even the Big Bang itself – should have sent ripples through space-time.
After all this time, these waves would be faint and hard to find, but they should all be a “buzz” echoing in the background of the Universe.
Now that we have confirmation that gravitational waves exist and can be detected – a discovery only six years old – scientists are looking for the background of gravitational waves. This could reveal a parcel on the history of the Universe – cracking it would be a major scientific breakthrough. And, although it is not easy, pulsars hold great promise.
It is a type of neutron star, spinning at incredibly high speeds and oriented in such a way that they emit emission beams from their poles as they do – like a cosmic beacon. These millisecond pulses are so regular that we can use delays in their timing for a range of potential applications. This is called a pulsar timing table.
Because gravitational waves distort space-time, they should, theoretically, produce minute delays in the synchronization of pulsars. This is what the NANOGrav team found in their data, and what the OzGrav team also looked for.
“The [gravitational wave] the background expands and shrinks the spacetime between pulsars and Earth, causing pulsar signals to arrive a little later (stretch) or earlier (shrink) than would otherwise occur if there weren’t gravitational waves, ”Shannon told ScienceAlert earlier this year.
The team analyzed data from Murriyang’s radio telescope in Parkes, Australia, and found deviations in the timing of the pulsar’s emission that we expected from the gravitational wave background. They also ruled out other potential sources of the signal, such as interference from Jupiter and Saturn.
However, we still don’t have enough data to confirm that we are actually looking at the background of gravitational waves, rather than regular pulsar noise, for example. We need more observations and data to determine if the signal is correlated between all the pulsars in the sky, which is going to take a lot more time and work.
“To find out if the observed ‘common’ drift has a gravitational wave origin,” said Goncharov, “or if the gravitational wave signal is deeper in noise, we need to keep working with new data from ‘an increasing number of pulsar synchronization matrices around the world. “
This work, and that of NANOGrav earlier this year, are the first steps towards this detection. It is an incredibly exciting time for gravitational wave astronomy.
The research was published in Letters from the astrophysical journal.
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