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Along with the great quests to find, and explain, dark energy and dark matter astronomers have a third task: finding the universe's missing baryonic (normal) matter, the matter we expect to see but don't. Now an innovative approach has detected a tiny portion of the missing matter is lurking quite close (by astronomical standards) to the Solar System, suggesting such pockets are quite common.
Unlike dark matter and dark energy, which we know must be fundamentally strange substances differing from the materials we are used to, the missing matter is expected to be ordinary gas and perhaps a little dust like the universe we can see. The problem is that when we look back to the early universe we can measure the amount of matter then present, but in more current observations half of it appears to be gone. Even allowing for the conversion of matter into energy in stars, there just isn't as much visible matter as we know must be there.
In the last few years, astronomers have achieved quite a bit of success in finding this missing matter, for example locating a lot of it in diffuse gas between galaxies hundreds of millions of light-years away. Nevertheless, some is still unaccounted for. Some have joked we need to look down the back of the couch and Sydney University PhD student Yaunming Wang has done the astronomical equivalent, locating a cloud of previously unknown material just 10 or so light-years from Earth, closer than all but the dozen or so nearest stars.
“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,” Wang said in a statement. Wang found it by looking for twinkling galaxies.
Astronomers have known for some time certain galaxies appear to shimmer when observed with radio telescopes. They concluded this is because radio waves from the galaxies are passing through some material, creating an effect comparable to starlight passing through our atmosphere, but on timescales of hours not milliseconds. Wang told IFLScience it had already been proven the distortions aren't coming from our own atmosphere, making them a product of something in space we can't see.
To investigate this, Wang and colleagues searched a 30 square degree field for twinkling galaxies and found six, five in a straight line. By checking other galaxies that don't twinkle, they report in Monthly Notices of the Royal Astronomical Society these five are being affected by a cloud of gas approximately a trillion kilometers (0.1 light-years) long but just 10 billion kilometers wide.
The gas is presumed to be hydrogen, since “That's what most of the stray material in the universe is,” Wang told IFLScience. It also must be very cold, or we would be able to detect it in other ways. Wang and co-authors suspect they've found a cloud of “hydrogen snow” that got stretched into its current shape by the gravity of a passing star.
“This is the first time that multiple ‘scintillators’ have been detected behind the same cloud of cold gas. In the next few years, we should be able to use similar methods with Australian Square Kilometre Array Pathfinder to detect a large number of such gas structures in our galaxy,” Wang's supervisor Professor Tara Murphy said.
Exciting as it is to detect such material so close to home, it fills only a tiny portion of the missing matter. Based on its size and the amount of twinkling induced the cloud is only thought to have as much mass as our own Moon.
