Dark Matter: One Of The Universe's Biggest Mysteries Isn't Invisible Anymore
Dark matter, along with its fellow mystery that scientists can't even explain, dark energy, is a strange thing. Well, strange to us humans, at least — it could be that right now, some alien species out there is having a hearty chuckle at the expense of the weird sentient apes on Earth that somehow can't figure out 95 percent of the universe. After all, dark energy takes up around 68 percent of everything the universe is made of, which leaves 27 percent for dark matter ... and a measly five percent for normal matter. Which, come to think of it, should probably be called 'abnormal matter', seeing as it's in a clear minority.
As Live Science tells us, dark matter as we currently understand it is basically a giant web that subtly "organizes" visible matter with its gravitational pull. Its single tendrils can be millions of light years long, and they act as "cosmic freeways" that collect normal matter. Some spots in space sit in massive "pools" of dark matter, and as such, they are homes to giant clusters of galaxies. But since dark matter doesn't emit light and the only way we know it's there is the fact that scientists think it's hanging around wherever normal matter isn't, there's no real way we can see it. Or ... is there?
Darkness matters
The version of dark matter/normal matter web that exists today is "a vast, complex network of filaments of matter" known as the cosmic web. Scientists have obviously studied it, and on January 29, 2020, one group of astronomers finally figured out how to untangle the web in a way that enables us to finally "see" dark matter. The key to the discovery were luminous red galaxies (LRGs), a type of giant super-galaxy that's usually found in the center of a particularly dense concentration of dark matter. They set out to look for the dark matter filaments connecting various LRGs by making a composite image of "thousands of pairs of LRGs," and after carefully taking all the light contribution from the normal matter into account, they could measure how much of it was visible in the image. With that information, they were able to look into the ways the filaments of dark matter were gently shifting the light and estimate the amount of dark matter present.
The results, as you can probably assume, are fairly groundbreaking. Not only were the team's calculations in line with theoretical predictions about dark matter's existence and properties, but they were also able to confirm that despite its name, dark matter isn't entirely dark. In fact, the filaments were found to have a very, very faint light output: For 351 sun's-worth of mass in the dark matter filaments, they put out one sun's worth of light. Oh, and they were also able to put together the above neat visualization of the filaments, allowing our puny human eyes to finally observe dark matter in a way they can handle. Hey, shouldn't we now rename it "dim but still kind of visible if you have the right tools matter?" No? Fair enough.