Cold gas cloud in our galaxy could be hiding universe's missing matter

Cold gas cloud in our galaxy c...
An artist's impression of a long, cold gas cloud discovered in the Milky Way
An artist's impression of a long, cold gas cloud discovered in the Milky Way
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An artist's impression of a long, cold gas cloud discovered in the Milky Way
An artist's impression of a long, cold gas cloud discovered in the Milky Way

By studying the twinkling of stars, astronomers in Australia have discovered a huge cloud of cold gas in our galaxy, not far from Earth. This invisible mass could provide new hints about where to find the universe’s missing matter.

When you tally up the contents of the universe, it turns out that we’re missing the vast majority of it. Almost 70 percent of everything is tied up in dark energy, the mysterious force that’s driving the acceleration of the expansion of the universe. Roughly 25 percent is thought to be dark matter, a strange substance that seems to interact only through gravity. And that leaves just five percent to be composed of regular (or baryonic) matter – and we’re even still missing almost half of that small fraction.

Astronomers have long been able to estimate how much matter should have been created in the Big Bang, but when they look to the skies there just doesn’t seem to be enough out there. Counting up all the stars, planets, asteroids, and other debris comes up about 40 percent short.

“We suspect that much of the ‘missing’ baryonic matter is in the form of cold gas clouds either in galaxies or between galaxies,” says Yuanming Wang, lead author of the new study. “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.”

So for this study, researchers from the University of Sydney turned to unconventional methods. When electromagnetic waves pass through gas they can become distorted. One of the most famous examples is how stars seem to twinkle (like a diamond in the sky, you might say), an effect caused by their light shimmering as it passes through Earth’s atmosphere.

The team tapped into this phenomenon by observing radio waves from distant galaxies, and studying how their signals shimmered. They discovered five of these “scintillators” in a line across the sky, and found that the all shared the same pattern of distortion, indicating that the signals were all passing through the same cold gas cloud on their way to us.

From this, the researchers were able to calculate that the cloud must be about 13 light-years long and 0.3 light-years wide, and it’s incredibly diffuse, containing only about the mass of the Moon. It’s also about 10 light-years away from Earth, which is relatively close in the grand scheme of things.

Of course, considering how much matter is missing this find isn’t a huge amount. But it presents a new way to find other clouds, which may be common across the universe. Other studies are searching for it in interstellar gas, examining the X-rays from pulsars or signals from fast radio bursts.

The research was published in the Monthly Notices of the Royal Astronomical Society.

Source: University of Sydney

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Chris Coles
Here in the South of the UK I have always been fascinated by finding hills with clay on top of the hills, beneath which is, effectively, an ancient sea bed, the top surface of the chalk, which in turn is as much as 1,000 feet deep. So I have wondered if the clay came from outer space, and if it did, might it have arrived via a cloud in space . . . food for thought?