Dark matter. You’ve probably heard of it, maybe in a Sci-Fi novel or movie, and you’ve probably wondered what it is exactly. Well, welcome to the club. Scientists have been asking themselves this question since its discovery in 1933. Dark matter is an invisible, mysterious substance that makes up 22% of the universe, but we know very little about it.
It has been difficult to study dark matter because of its properties. It does not emit, absorb, or reflect light, making it “dark” and virtually indetectable except for its effects on objects.
Scientist Fritz Zwicky discovered dark matter when he measured the visible mass of a cluster of galaxies and found that it was much too small to prevent the galaxies from escaping the gravitational pull of the cluster. Some invisible force was acting like glue and holding them in place. Zwicky called the glue dunkle Materie, or dark matter in German.
Think of a cluster as a merry-go-round. The weight of the objects and their positions determine the speed at which they rotate. Scientists were expecting to find that objects at the cluster’s edge rotated slower than those near the center like a merry-go-round. Instead, they found objects rotating at around the same speed regardless of where they are. This only makes sense if the boundary stars are affected by the gravity of an unseen mass, aka dark matter.
Years later, in 1970 scientists Vera Rubin and Kent Ford would provide further evidence for the presence of dark matter by studying the rotation speeds of individual galaxies. Their studies also confirmed that although the galaxies should be flung apart dark matter was holding them together.
There are a number of theories as to what dark matter is made up of. It was proposed that dark matter could be “failed stars” known as brown dwarfs, or neutron stars, or black holes. The problem with these theories is that there are not enough brown dwarfs to account for dark matter, and neutron stars and black holes are also rare occurrences.
Recently, it has been proposed that dark matter could be made up of hypothetical particles called axions. Axions are thought to be light enough that they travel through space like waves. However, axions have yet to be detected. Another popular theory is WIMPs, (weakly interacting massive particles). These hypothetical heavy slow-moving particles have also not been detected yet. Scientists are still left with only theories as to the particles that make up dark matter.
The questions surrounding dark matter remain a reminder of how little we know about the universe. NASA’s webpage on dark matter concludes “That's what makes dark matter exciting: It's still one of the great mysteries of science.”
You’ve been listening to Western Slope Skies, produced by the Black Canyon Astronomical Society and KVNF Community Radio. This feature was written and recorded by Sierra Lastine, a junior studying English at Colorado Mesa University.
Works Cited
“Dark Matter and Dark Energy’s Role in the Universe.” Science, 3 May 2021, www.nationalgeographic.com/science/article/dark-matter?loggedin=true&rnd=1684369994188.
Dunbar, Brian. “What Is Dark Matter?” NASA, 5 June 2013, https://www.nasa.gov/audience/forstudents/9-12/features/what-is-dark-matter.html.
Nalick, Jon. “What Is Dark Matter, and Where Is It Hiding?” Caltech Magazine, 10 June 2021, magazine.caltech.edu/post/where-is-dark-matter-hiding.
Tomaswick, Andy. “If Dark Matter Is Made of Axions, This Could Be the Detector That Finds Them.” Universe Today, 9 Dec. 2022, www.universetoday.com/159115/if-dark-matter-is-made-of-axions-this-could-be-the-detector-that-finds-them.
