“We aren’t quite sure what the strange cloud is, but one possibility is that it could be a hydrogen ‘snow cloud’ disrupted by a nearby star to form a long, thin clump of gas,” said Artem Tuntsov, with Australia’s Manly Astrophysics Institute, about a hitherto undetected invisible stream of cold gas in the Milky Way about 10 light years from Earth a trillion kilometers long and 10 billion kilometers wide, only weighing about the mass of our Moon. Hydrogen freezes at about minus 260 degrees and theorists have proposed that some of the universe’s missing baryonic matter –the form of matter of which stars and planets and we Homo sapiens are composed–could be locked up in these hydrogen ‘snow clouds’.
Enduring, Unsolved Problem
Astronomers have spent decades looking for something common sense says would be hard to miss: about a third of the “normal,” baryonic, matter in the Universe (distinct from the still-mysterious dark matter.) Scientists have calculated how much normal matter—meaning hydrogen, helium and other elements— the normal matter that made its way into cosmic dust, gas and objects such as stars and planets that telescopes can see in the present-day universe–existed just after the Big Bang. The enduring, unsolved problem is that when astronomers add up the mass of all the normal matter in the present-day universe about a third of it can’t be found.
Where did the universe stash the Missing Matter?
“If we find this missing mass, we can solve one of the biggest conundrums in astrophysics,” said Orsolya Kovacs at the Harvard- Smithsonian Center for Astrophysics (CfA), who was not involved in the Australian study. “Where did the universe stash so much of its matter that makes up stuff like stars and planets and us?”
Now, for the first time, astronomers led by Yuanming Wang, a doctoral candidate in the School of Physics at the University of Sydney, who developed an ingenious method using distant galaxies as ‘scintillating pins’ to locate and identify the hitherto undetected stream of cold gas hiding a piece of the Milky Way’s missing matter.
“We suspect that much of the ‘missing’ baryonic matter is in the form of cold gas clouds either in galaxies or between galaxies,” said Wang, who looked for radio sources in the distant background to see how they ‘shimmered’. “This 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.”
“We 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,” Wang said referring to the phenomenon that occurs when radio waves pass through matter, it also affects their brightness. It was this ‘scintillation’ that Ms Wang and her colleagues detected. “However, we have now developed a method to identify such clumps of ‘invisible’ cold gas using background galaxies as pins,” Wang added.
The data to find the gas cloud was taken using the CSIRO’s Australian Square Kilometer Array Pathfinder (ASKAP) radio telescope in Western Australia, with its wide field of view, seeing tens of thousands of galaxies in a single observation that allowed the team to measure the shape of the gas cloud.
“This is the first time that multiple ‘scintillators’ have been detected behind the same cloud of cold gas,” said Murphy. “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.”
“This is a brilliant result for a young astronomer,” said Wang’s supervisor, Professor Tara Murphy.”This is a brilliant result for a young astronomer. We hope the methods trailblazed by Yuanming will allow us to detect more missing matter. We hope the methods trailblazed by Yuanming will allow us to detect more missing matter.”
Image at the top of the page shows the largest coherent gas structure we know of in the Milky Way, organized not in a ring but in a massive, undulating filament The Radcliffe Wave/Harvard University, courtesy of Alyssa Goodman, Harvard University