March 7, 2021

An astrophysics student finds lost galactic matter


Artist's impression of a gas cloud caused by a tide

Artist’s impression of a gas cloud caused by a tide
University of Sydney

Astronomers have used distant galaxies as “sparkling pins” for the first time to locate and identify a part of the lost matter of the Milky Way.

For decades scientists have been intrigued by the fact that they couldn’t explain all the matter in the universe as theory predicts. While most of the mass in the universe is believed to be mysterious dark matter and dark energy, 5 percent is “normal matter” that makes up stars, planets, asteroids, and even ourselves. This is known as baryonic matter. However, direct measurement has only accounted for about half of the expected baryonic matter.

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

The results, published in Monthly Notices of the Royal Astronomical Society, offer a promising way for scientists to track lost matter from the Milky Way. “We suspect that much of the ‘missing’ baryonic matter is as clouds of cold gas, either in galaxies or between galaxies“said Wang, who is doing his PhD at the Sydney Institute of Astronomy.” This gas is undetectable using conventional methods, as it does not emit visible light of its own and is too cold to be detected by radio astronomy, “he said.

What the astronomers did was look for radio sources in the distant background to see how they glowed. “We found five flickering radio sources in a giant line in the sky. Our analysis shows that their light must have passed through the same cold group of gas,” said Wang. Just as visible light is distorted as it passes through our atmosphere To give stars their brightness, when radio waves pass through matter, it also affects their brightness. It was this “twinkle” that Wang and his colleagues detected..

Dr Artem Tuntsov, co-author of 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’ interfered with by a nearby star to form a long, thin group of gas. “Hydrogen freezes at around minus 260 degrees and theorists have proposed that some of the baryonic matter missing from the universe could be locked up in these” snow clouds. “Hydrogen. They are almost impossible to detect directly.” However, we have now developed a method to identify such groups of cold ‘invisible’ gas using background galaxies as pins, “Wang said.

Data to find the gas cloud was taken using CSIRO’s Australian Square Kilometer Array Pathfinder (ASKAP) radio telescope in Western Australia. Dr. Keith Bannister, CSIRO’s senior research engineer, said: “The wide field of view from ASKAPBy seeing tens of thousands of galaxies in a single observation, it allowed us to measure the shape of the gas cloud. ”

Professor Murphy said: “This is the first time that multiple ‘scintillators’ have been detected behind the same cold gas cloud. In the next few years, we should be able to use similar methods with ASKAP to detect a large number of structures of that gauze in our galaxy“.

Wang’s discovery adds to a growing set of tools for astronomers in their search for the universe’s lost baryonic matter. This includes a method published last year by the late Jean-Pierre Macquart of Curtin University, who used CSIRO’s ASKAP telescope to estimate a portion of matter in the intergalactic medium using fast radio bursts as ‘cosmic weigh stations’. .

.



Source link