ASKAP helps to unveil Universe's missing matter

Astronomers have used Fast Radio Bursts (FRBs) to detect “missing matter” -not to be confused with dark matter-, long predicted to exist in the Universe and hinted at in previous measurements but never detected - until now. The researchers detected missing “normal” matter in the vast space between stars and galaxies. Their findings are reported in the journal Nature.

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, but when we looked out into the present Universe, we couldn’t find half of what should be there.”

DID YOU KNOW?

The Universe is believed to be made up of dark energy, dark matter and “normal matter” – the latter being everything we can see, Earth, planets, stars, etc. The best available current models estimate dark energy to represent about 68% of the universe, dark matter 27% and normal matter only 5%. But “normal matter” also has its own invisibility problem and of that 5%, we can only see about half of it.

They thought the matter should be out there, but couldn’t detect it. That posed a problem – how do you prove something is present when you can’t see it?

The researchers were able to directly detect the missing matter using fast radio bursts which they detected and then localised to their origins using CSIRO’s Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope.

This was accomplished by first measuring the delay between the wavelengths of an FRB using ASKAP, and then calculating the distance of the FRB from Earth. The delay between wavelengths signals the presence of matter, and can be used to work out its density as long as you have the distance from Earth.

A whole network of FRBs was used in the study, acting as “cosmic weigh stations”.

Dr Keith Bannister from CSIRO, Australia’s national science agency, who designed the pulse capture system used in the research, said that when fast radio bursts arrive at the telescope, ASKAP records a “live action replay” 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.

Associate Professor Macquart said this result underscores the strong connection between instrument design and science.

ASKAP's success is just like Formula 1, no driver can win a championship without the backing of a whole team of engineers and mechanics.

Associate Professor Jean-Pierre Macquart, ICRAR-Curtin

“The team working on FRBs with ASKAP is a tight-knit collaboration – it harnesses expertise spanning five continents that exploits the best the world has to offer in terms of radio, optical, simulation and theory.”

The FRB travels from its host galaxy to Earth.

Credit: ICRAR

When travelling through completely empty space, all wavelengths of the FRB travel at the same speed, but when travelling through the missing matter, some wavelengths are slowed down.

Credit: ICRAR

A network of FRBs was used to measure the density of the missing matter.

Credit: ICRAR

The density of missing matter is calculated using the distance of the FRB from Earth, and the delay between the wavelengths of the FRB as detected by ASKAP.

Credit: ICRAR

By ICRAR and CSIRO