We call it outer space, but that really paints the wrong picture of just how much stuff is really out there. Yes, the distances between objects are usually bigger than we can truly comprehend. Sure, there’s a lot of cosmic territory that look empty, neither reflecting or emitting any kind of detectable energy, from light to heat. However, the movement of the things we can see indicates that there’s a lot more matter in the universe, even it’s not directly visible. Researchers have long trusted that gravity hasn’t been fooling us, and now two teams have finally found some of that imperceptible stuff that scattered throughout space.
Deciphering the dark
When we look out at the universe with our eyes, telescopes, microwave detectors and more, we really only see about 20 percent of what we know must be out there. The 80 percent that we can’t directly observe is referred to as dark matter, since it never shows up as a source of light or other energy when we look. However, the behavior of planets and stars would only make sense if they were being influenced by the gravity of a lot unseen material. As confident as astrophysicists are about the gravitational forces that should be shaping the universe, it’s always good to try to validate one’s models, even if it’s just to confirm what was mostly already known.
Cranking up the contrast
In this case, two teams of researchers have independently imaged clouds of tiny particles called baryons. Baryons are smaller than a proton, consisting of only three quarks. That size reduces their chances of interacting with something like visible light, which is part of why we don’t see the huge swaths of them floating around space. To make things even trickier, they’re distributed in diffuse clouds between galaxies, making whatever traces they’d leave on their surroundings even harder to detect.
To make these baryon clouds more obvious, both teams used a technique which essentially upped the contrast on our readings of two galaxies that had been observed by the Planck satellite in 2015. Both groups overlaid the observed data on itself over a quarter-million times, making the clustered baryons more obvious to detection, although even then they weren’t directly visible. Instead, researchers had to rely on the Sunyaev-Zel’dovich effect, which is when light from the big bang itself is scattered by passing hot gas. So in the end, the teams were only able to see strands of scattered light connecting two galaxies, but that was enough to confirm the presence of otherwise invisible matter.
This doesn’t solve all of our dark matter mysteries, but it does account for a significant chunk of what was otherwise unconfirmed sources of gravity. There are hypothesis about what other kinds of particles are helping fill the cosmic void, but for now it’s nice knowing that we’ve been on the right track with our understanding of gravity so far, and that only half the universe’s mass can’t be explained. Yet.
Source: Half the universe’s missing matter has just been finally found by Leah Crane, New Scientist