Put simply, dark matter is a substance of unknown nature that produces an exceptional amount of gravity and yet does not interact with light in any currently known way. Which is how it got the name “dark matter,” as it’s invisible to the entire electromagnetic spectrum. Though its existence is still only hypothetical, and it has never been directly observed quite yet, the shadowy, spectrum-avoiding enigma is one of the leading hypotheses to the problem of the universe containing far more mass than is directly observable—the “missing mass” problem.
The “missing mass” problem in the universe was first discovered in 1933 but wasn’t really understood until 1937 when Fritz Zwicky, who, on an unrelated note, was apparently kind of a dick*,
discovered more comprehensive data to explain the apparent lack of matter. He studied the velocities of galaxies within the massive Coma Berenices cluster, or the Coma cluster. When he calculated the average velocity of some of the thousands of galaxies within the Coma cluster, his data showed that their velocities were unusually high. The problem arose from the fact that, even with all of the visible matter within the entire mega-cluster, the combined mass still wasn’t large enough to account for the galaxies high velocities. Clearly some matter was “missing.” This lead Zwicky to the conclusion that there had to be some sort of invisible shit floating around in space. This discovery effectively crowned Zwicky the “father of dark matter.”
Over the past 80 years since Zwickys substantial discovery, and despite the amazing contributions by other astronomers and astrophysicists (notably, Vera Rubin), dark matter still remains an ever elusive bastard. The most recent and agreed upon research on the sneaky little bastards posits that dark matter is made up of weakly interacting massive particles, or WIMPs (nerd jokes), that interact through gravity and the weak force. WIMPs are still only hypothetical but their existence is allowed in nature through the theory of supersymmetry. WIMPs aren’t the only possibility to comprise dark matter though. A couple of other hypothetical particle contestants similar to WIMPs are axions and sterile neutrinos.
Current estimates place dark matter content in the universe at around 26.8%.
As how science is supposed to work, dark matter is not an 100% conclusive answer and its validity can definitely still be questioned. A small group of astronomers hypothesize that certain methods can account for the extra mass in the universe without the use of any additional matter. MOND, TeVeS, and conformal gravity are some of the top counter-arguments to the dark matter hypothesis (more on that in Part 2).
This is seriously just scratching the surface on what dark matter truly is and the methods used to discover it. I’ve also left out explanations of some hefty topics due to my attempt at avoiding dryness. Axions, sterile neutrinos, supersymmetry, MOND, TeVeS? What the flying fuck are all of those? I’ll tackle all of those in,“What the F*ck is Dark Matter? Part 2: The Technical Shit.” Depending on how things play out, there may even be a Part 3. Overall though, I hope this article sheds a wee bit of light on what dark matter is. If you’re still confused, just let me know! One cannot better themselves without constructive criticism.
*No disrespect meant towards Zwicky and his family, only poking fun. Zwicky’s daughter is somewhat of a crusader for her fathers integrity and I think that’s badass.
Dark matter illustration credit: Jakub Grygie on ArtStation
WMAP background radiation picture credit: NASA/WMAP
Additional sources: Origins by Neil DeGrasse Tyson
(Originally posted here: http://fyeahastrophysics.com/post/168364460091/what-the-fck-is-dark-matter-part-1)