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Astronomers have for the first time used distant galaxies as 鈥榮cintillating pins鈥� to locate and identify a piece of the Milky Way鈥檚 missing matter.

For decades, scientists have been puzzled as to why they couldn鈥檛 account for all the matter in the universe as predicted by theory. While most of the universe鈥檚 mass is thought to be mysterious dark matter and dark energy, 5 percent is 鈥榥ormal matter鈥� that makes up stars, planets, asteroids, peanut butter and butterflies. This is known as baryonic matter.

However, direct measurement has only accounted for about half the expected baryonic matter.

Yuanming Wang, a doctoral candidate in the School of Physics at the University of Sydney, has developed an ingenious method to help track down the missing matter. She has applied her technique to pinpoint a hitherto undetected stream of cold gas in the Milky Way about 10 light years from Earth. The cloud is about a trillion kilometres long and 10 billion kilometres wide but only weighing about the mass of our Moon.

The results, published in the , offer a promising way for scientists to track down the Milky Way鈥檚 missing matter.

鈥淲e suspect that much of the 鈥榤issing鈥� baryonic matter is in the form of cold gas clouds either in galaxies or between galaxies,鈥� said Ms Wang, who is pursuing her PhD at the .

鈥淭his gas is undetectable using conventional methods, as it emits no visible light of its own and is just too cold for detection via radio astronomy,鈥� she said.

What the astronomers did is look for radio sources in the distant background to see how they 鈥榮himmered鈥�.

鈥淲e found five twinkling radio sources on a giant line in the sky. Our analysis shows their light must have passed through the same cold clump of gas,鈥� Ms Wang said.

Just as visible light is distorted as it passes through our atmosphere to give stars their twinkle, when radio waves pass through matter, it also affects their brightness. It was this 鈥榮cintillation鈥� that Ms Wang and her colleagues detected.

, a co-author from , said: 鈥淲e aren鈥檛 quite sure what the strange cloud is, but one possibility is that it could be a hydrogen 鈥榮now cloud鈥� disrupted by a nearby star to form a long, thin clump of gas.鈥�

Hydrogen freezes at about minus 260 degrees and theorists have proposed that some of the universe鈥檚 missing baryonic matter could be locked up in these hydrogen 鈥榮now clouds鈥�. They are almost impossible to detect directly.

鈥淗owever, we have now developed a method to identify such clumps of 鈥榠nvisible鈥� cold gas using background galaxies as pins,鈥� Ms Wang said.

Ms Wang鈥檚 supervisor, Professor Tara Murphy, said: 鈥淭his is a brilliant result for a young astronomer. We hope the methods trailblazed by Yuanming will allow us to detect more missing matter.鈥�

The data to find the gas cloud was taken using the CSIRO鈥檚聽聽(ASKAP) radio telescope in Western Australia.

, Principal Research Engineer at CSIRO, said: 鈥淚t is ASKAP鈥檚 wide field of view, seeing tens of thousands of galaxies in a single observation that allowed us to measure the shape of the gas cloud.鈥�

Professor Murphy said: 鈥淭his is the first time that multiple 鈥榮cintillators鈥� have been detected behind the same cloud of cold gas. In the next few years, we should be able to use similar methods with ASKAP to detect a large number of such gas structures in our galaxy.鈥�

Ms Wang鈥檚 discovery adds to a growing suite of tools for astronomers in their hunt for the universe鈥檚 missing baryonic matter. This聽聽last year by the late Jean-Pierre Macquart from Curtin University who used CSIRO鈥檚 ASKAP telescope to estimate a portion of matter in the intergalactic medium using fast radio bursts as 鈥榗osmic weigh stations鈥�.

Ms Wang and Professor Murphy鈥檚 research was done in collaboration with CSIRO, Manly Astrophysics, the University of Wisconsin-Milwaukee and the ARC Centre of Excellence for Gravitational Wave Discovery, OzGrav.