The lead author of the study, PhD student Yuanming Wang. Photo: Louise Cooper
Astronomers have for the first time used distant galaxies as “scintillating pins” to locate and identify a piece of missing matter in the Milky Way.
For decades, scientists have been puzzled as to why they could not explain all matter in the universe as the theory predicted. While most of the mass of the universe is considered to be mysterious dark matter and dark energy, 5% is “normal matter” that makes up stars, planets, asteroids, peanut butter and butterflies. This is known as baryonic matter.
However, direct measurement accounted for only about half of the expected baryonic matter.
Yuanming Wang, a doctoral candidate at the School of Physics at the University of Sydney, has developed an ingenious method to help spot the missing problem. She applied her technique to identify a hitherto undetected cold gas stream in the Milky Way, about 10 light-years from Earth. The cloud is about a trillion kilometers long and 10 billion kilometers wide, but it weighs only around our moon.
The results, published in Monthly notifications from the Royal Astronomical Society, offers scientists a promising way to detect the missing matter of the Milky Way.
“We suspect that much of the ‘missing’ baryonic matter is in the form of cold gas clouds, either in galaxies or between galaxies,” said Ms. Wang, who is pursuing a doctorate at the Sydney Institute of Astronomy.
“This gas is undetectable using conventional methods because it does not emit visible light itself and is too cold to detect by radio astronomy,” she said.
What astronomers have done is to search for radio sources in the distant background to see how they “shone.”
“I found five glittering radio sources on a huge line in the sky. Our analysis shows that their light must have passed through the same cold pile of gas, “said Ms. Wang.
Just as visible light is distorted as it passes through our atmosphere to give stars its sparkle, when radio waves pass through matter, it also affects their brightness. This “scintillation” was detected by Ms. Wang and her colleagues.
Dr. Artem Tuntsov, a co-author at Manly Astrophysics, said: “We’re not 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. ”
Hydrogen freezes at about minus 260 degrees, and theorists have suggested that some of the universe’s missing baryonic matter could be trapped in these “snow clouds” with hydrogen. I am almost impossible to detect directly.
“However, we have now developed a method to identify such clusters of ‘invisible’ cold gas using background galaxies as pins,” said Ms. Wang.
Ms. Wang’s supervisor, Professor Tara Murphy, said: “This is a brilliant result for a young astronomer. We hope that the methods revealed by Yuanming will allow us to detect more missing matter. ”