Daily Times

Astronomers have used mysterious fast radio bursts to solve a decades-old mystery of “missing matter,” long predicted to exist in the universe, but never before detected.

Lead author Associate Professor Jean-Pierre Macquart, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) said astronomers have been searching for the missing matter for almost 30 years.

“We know from measurements of the Big Bang how much matter there was in the beginning of the universe,” he said. “But when we looked out into the present universe, we couldn’t find half of what should be there. It was a bit of an embarrassment. Intergalactic space is very sparse. The missing matter was equivalent to only one or two atoms in a room the size of an average office. So it was very hard to detect this matter using traditional techniques and telescopes.”

The radiation left over from the Big Bang that can be detected throughout the Universe – the Cosmic Microwave Background – lets us know how much baryonic matter was around at the beginning of the Universe. But a few decades ago, when astronomers started to compare that to the baryonic matter we can detect now, they only found about half as much as expected.

Where the rest went has been a mystery ever since, but we’ve had hints. Techniques such as analysis of the light travelling from distant quasar galaxies have revealed very specific, small amounts of atomic hydrogen, or material close to galaxies.

The scattering of the Cosmic Microwave Background photons by galaxy clusters, has revealed material close to galaxies, or within filamentary structures.

But farther away from galaxies, dark stretches of space are much more difficult to probe.

“Intergalactic space is very sparse. The missing matter was equivalent to only one or two atoms in a room the size of an average office,” explained astronomer Jean-Pierre Macquart of the Curtin University, Australia node of the International Centre for Radio Astronomy Research.

The fast radio bursts used in the study were discovered using ASKAP, which is located at the Murchison Radio-astronomy Observatory in outback Western Australia. The international team involved in the discovery included astronomers from Australia, the United States and Chile. ASKAP is a precursor for the future Square Kilometre Array (SKA) telescope. The SKA could observe large numbers of fast radio bursts, giving astronomers greater capability to study the previously invisible structure in the universe.

“A census of baryons in the universe from localized fast radio bursts” was published in Nature on May 28, 2020.