Lead author of the study, PhD student Yuanming Wang. Photo: Louise Cooper
For the first time, astronomers have used distant galaxies as ‘sparkling pins’ to locate and identify some of the Milky Way’s missing matter.
For decades, scientists have wondered why they couldn’t explain all of the matter in the universe, as predicted by the theory. While most of the universe’s mass is believed to be mysterious dark matter and dark energy, 5 percent is ‘normal matter’ made up of stars, planets, asteroids, peanut butter, and butterflies. This is known as baryonic matter.
However, direct measurement explained only about half of the expected baryonic matter.
Yuanming Wang, a PhD student at the University of Sydney’s School of Physics, has developed an ingenious method to locate the missing matter. She has used her technique to locate a hitherto undiscovered stream of cold gas 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 about the mass of our moon.
The results, published in the Monthly Communications from the Royal Astronomical Society, provide scientists with a promising way to track down 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 Ms. Wang, who is currently PhD at the Sydney Institute for Astronomy.
“This gas is not detectable by conventional methods because it does not emit visible light itself and is simply too cold for radio astronomy detection,” she said.
What the astronomers did was search for radio sources in the distant background to see how they “sparkled.”
‘We found five twinkling radio sources in a gigantic line in the sky. Our analysis shows that their light must have passed through the same cold lump of gas, ”said Ms. Wang.
Just as visible light is distorted as it passes through our atmosphere to make stars twinkle, it also affects their brightness when radio waves pass through matter. It was this “sparkle” that Ms. Wang and her colleagues discovered.
Dr. Artem Tuntsov, a co-author of Manly Astrophysics, said: “We don’t know exactly what the strange cloud is, but one possibility is that it could be a hydrogen ‘snow cloud’ perturbed by a nearby star to create a long , thin lump of gas. “
Hydrogen freezes at about minus 260 degrees and theorists have proposed that some of the universe’s missing baryonic matter could be trapped in these “snow clouds” of hydrogen. They are almost impossible to detect immediately.
“However, we have now developed a method to identify such clumps of ‘invisible’ cold gas using background galaxies such as pins,” said Ms. Wang.
Ms. Wang’s supervisor, Professor Tara Murphy, said, “This is a wonderful result for a young astronomer. We hope that Yuanming’s pioneering methods will enable us to detect more missing matter. “