Big Bang missing matter finally found in WA breakthrough needed to better map our universe

After almost 30 years of searching the universe, astronomers using a state-of-the-art telescope in Western Australia have finally solved the mystery of “missing matter” tracing back to the Big Bang.

The missing ‘normal’ matter, the same protons and neutrons that make up stars, planets and humans, has long been predicted to exist in the vast space between stars and galaxies but never detected.

But now it has been found by the Australian Square Kilometre Array Pathfinder radio telescope at the Murchison Radio-astronomy Observatory in WA’s Mid-West, according to Curtin University Associate Professor Jean-Pierre Macquart, from the International Centre for Radio Astronomy Research.

“We were able to look into the early universe and see how much matter there was but in the present day universe, some 13-point-something billion years since the Big Bang, we weren’t able to find the matter,” Professor Macquart said.

“A good analogy is that it’s like a magic trick: you go to a magic show and the magician shows you all this stuff – the rabbit at the beginning of the show – and somehow your eyes get distracted and halfway through the show you realise the rabbit’s disappeared but you don’t know where it’s gone and this was the problem that we faced.

“We were able to see that matter but in the present day universe it had gone into that space between galaxies, where it was incredibly hard to find.”

The key to unlocking the mystery was the phenomenon known as fast radio bursts (FRBs), in which brief flashes of energy travelling through space were altered when they came into contact with the missing matter.

“There were a bunch of us around the world that when fast radio bursts were discovered a light went off in our heads and we said ‘ah that’s the way to find all that missing matter, but it’s all very well to have that realisation it was another thing entirely to go and find these things, figure out which galaxies they came from, measure their distances and then do the calculation,” Professor Macquart said.

“So that had to wait until now and the advent of this Australian SKA Pathfinder.”

He said Parkes radio telescope – ‘The Dish’ in western New South Wales – detected a lot of the early fast radio bursts from about 2007.

“So people were seeing dispersion in these fast radio bursts before but they didn’t know what to attribute it to,” Professor Macquart said.

“It really needed ASKAP’s ability to find which galaxy they came from.

“You really need the distances to say 'aha, I know how much matter this has gone through' but I have to know over what distance of the universe it’s travelled in order to measure the density of stuff that it’s gone through, so that’s the crucial thing.”

To give an example of how vast intergalactic space was, “the missing matter was equivalent to only one or two atoms in a room the size of an average office”, the rest being made up of dark matter, which remains elusive and accounts for about 85 per cent of the total matter in the universe.

The international team involved in the discovery are hoping that the future Square Kilometre Array telescope, combining the the power of the Murchison Radio-astronomy Observatory with one in South Africa, will observe lots of fast radio bursts and give astronomers greater capability to create enough sightlines to make a tomographic reconstruction of the previously invisible structure of the universe.

“What our measurements have not told us is where exactly all that matter is," Professor Macquart said.

“We know it’s out there in the stuff between galaxies but we don’t know precisely; where is it close to galaxies? Is it way out in the vast immenseness that stretches midway between these galaxies, exactly where is it?

“Because the reason this is interesting is because this matter is the stuff which falls on the galaxies to form new stars and planets and solar systems, like our own, but the matter also gets expelled out into galactic space.

“So it’s like a cosmic ecosystem.”

Scientists also don’t yet know what causes the FRBs, which appear to come from random directions in the sky and last for just milliseconds.

Yet they believe the bursts’ energy is equivalent to the amount released by the sun over 80 years.

“The radiation from fast radio bursts gets spread out by the missing matter in the same way that you see the colours of sunlight being separated in a prism,” Professor Macquart said.

“And that’s because the light travelling through glass travels at different speeds, that is: the blue light travels different speeds with respect to the red light. That’s the process of dispersion and that’s exactly the same process that these FRBs have been subject to it’s just instead of travelling through glass they’ve travelled through this missing matter.

“The interesting thing about this missing matter: it pretty much is everywhere, it pervades all of the space between galaxies.”

The bursts were not always easy to detect as astronomers didn’t know when and where to look for them, which is why Melbourne’s Swinburne University of Technology Associate Professor Ryan Shannon said the ASKAP was needed.

“ASKAP both has a wide field of view, about 60 times the size of the full moon, and can image in high resolution,” he said.

Dr Keith Bannister from Australia’s national science agency, CSIRO, which designed the ASKAP’s pulse capture system, said the telescope recorded a live action replay of the burst “within a fraction of a second”.

“This enables the precision to determine the location of the fast radio burst to the width of a human hair held 200m away,” he said.

It took nine months to collect six FRBs, whose distances they could calculate, to track down the ‘normal’ matter.

“It’s a small angle,” Professor Macquart said.

“The full moon is ½ a degree across so what we’re measuring down to is about 1/36,000 of a degree.

“But we need that precision to say which galaxy it came from; that‘s the key point.”

They then collaborated with astronomers using optical telescopes in Chile or on top of Mauna Kea in Hawaii to give them the distances of the galaxy.

“And presto you’ve got your measurement of the density of this stuff in the universe,” Professor Macquart said.

“What we’ve done here is basically weighed a universe with our measurements. And finally the sums agree with what we thought was there in the early universe.”

The findings have been published in the journal Nature on Thursday, with co-author Professor J. Xavier Prochaska, from the University of California in Santa Cruz calling it “the key breakthroughs” needed to solve the mystery.

While excited by the breakthrough, it was also a relief given that it was “a bit of an embarrassment”.

“This has been a problem that has been hanging around and it’s nice to be able to draw a line under the number and say with some confidence well, we’ve found it and now we think we know we’re doing," Professor Macquart said.

"But there are so many more steps to be done: where is that matter? What’s it doing?

"Like so many things in science it’s like peeling an onion, you remove one layer and you find a whole stack more.”