A lot of kids (and maybe adults) are scared of the dark. Most of us get over it once we realize there isnâ€™t a monster hiding in the closet or under the bed. But then scientists announce another finding about dark matter and we all are back peering from under the sheets.
Dark matter is some mysterious stuff that makes up about 75% of all of the matter in the Universe. That means that all of the stars, galaxies, people â€“ everything we can account for with every telescope we have -- only makes up a minority of the cosmos. (Thereâ€™s also something even more dominant in the Universe called dark energy, but we wonâ€™t go into that here.)
Back to the latest: scientists have announced they have found something that makes them question what little they thought they knew about dark matter. This system, known as Abell 520, is a place where at least two clusters of galaxies have collided. The result is a mess. Galaxies have been separated from the hot gas that surrounded them, but the galaxies apparently have also been torn apart from the dark matter. According to what scientists thought they knew about dark matter, this isnâ€™t supposed to happen. So, it turns out that we all â€“ including astronomers and physicists -- have something to be scared of the dark about.