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Australian scientists have heralded a new era of astronomy as they inch closer to proving the existence of a type of wave humming throughout the cosmos that could lead to the most detailed ever picture of the very birth of the universe.
Using data from the Parkes radio telescope, scientists from the CSIRO and Swinburne University collected their strongest evidence yet that low-frequency gravitational waves ripple across the fabric of space-time.
An animation showing pulsars – galactic “lighthouses” – emitting reliably timed beams of radiation, which can be detected by the Parkes radio telescope.Credit: OzGrav
These waves are sometimes referred to as gravitational wave background – the background “hum” of the universe that could hold secrets about its formation. Astronomers theorise these waves are emitted by pairs of supermassive black holes orbiting each other at the centre of colliding galaxies.
Another theory goes that the low-frequency gravitational waves were generated just after the Big Bang, right when the “inflation” or early exponential expansion of the universe began. If that bears out, these signals could be analysed to bring scientists to the start of the known universe.
Analysing electromagnetic radiation only gets astronomers to about 400,000 years after the Big Bang. The gravitational waves, if they are indeed relics of the early universe, could contain information that brings us within a nanosecond.
“It’s huge because it is the starting point of an era of nanohertz frequency gravitational wave astronomy,” said co-author of the new research, Swinburne University’s Dr Daniel Reardon.
“It means using gravitational waves to study things like binary supermassive black holes, maybe inflation, maybe cosmic strings, we really don’t know. But it really just kickstarts the era.”
The detection of the gravitational waves is made possible by spinning neutron stars that emit beams of radiation called “pulsars”. They’re exceptional tools for astronomers because the fluctuations in the regular pulsar beams can be used to detect other elements in space.
“We use them as incredibly stable lighthouses, out there in the galaxy,” co-author Dr Andrew Zic from the CSIRO said.
The Parkes telescope has been building a dataset of about 30 pulsar beams since 2004 (when Zic was nine years old). That allowed astronomers to detect minute anomalies or delays in the beams caused by the low-frequency gravitational waves they’re hunting – which may only ripple past earth once in a decade.
The CSIRO’s Parkes radio telescope has been tracking pulsar beams in the southern sky since 2004.Credit: Alex Cherney
“The strength of the signal is very small,” Reardon said. “The kinds of time delays that we’re seeing over that 18 years is less than a microsecond.”
The research is part of a global effort to co-ordinate pulsar timing. The contribution from Australia is key because the Parkes telescope monitors a set of pulsar “lighthouses” that the Northern Hemisphere doesn’t have in its sky.
This week an international consortium of consortia – the International Pulsar Timing Array – will release co-ordinated data that brings astronomers close to proving their detection of the low-frequency waves.
“The IPTA data release will have 115 pulsars in total, way more than what any individual group has,” Zic said. “It will be the most sensitive dataset we can possibly dream up for this work.”
Even if the waves didn’t originate from the Big Bang as theorised, they’ll bring unprecedented understanding of how the universe formed.
“It’s really the binary black holes in the early universe that are expected to be producing these gravitational waves and that contribute to this random sea of waves that we’re seeing,” Reardon said.
“Supermassive black holes are really the engines of the galaxy. They feed on gas, and they emit lots of energy and affect star formation for the entire galaxy. So understanding supermassive black holes has very important consequences for our understanding of the formation history of the universe.”
Liam Mannix’s Examine newsletter explains and analyses science with a rigorous focus on the evidence. Sign up to get it each week.
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