In the 1930s, a Swiss astronomer named Fritz Zwicky noticed that galaxies in a distant cluster were orbiting one another much faster than they should have been given the amount of visible mass they had. He proposed than an unseen substance, which he called dark matter, might be tugging gravitationally on these galaxies.
Since then, researchers have confirmed that this mysterious material can be found throughout the cosmos, and that it is six times more abundant than the normal matter that makes up ordinary things like stars and people. Yet despite seeing dark matter throughout the universe, scientists are mostly still scratching their heads over it. Here are the 11 biggest unanswered questions about dark matter.
What is dark matter?
First and perhaps most perplexingly, researchers remain unsure about what exactly dark matter is. Originally, some scientists conjectured that the missing mass in the universe was made up of small faint stars and black holes, though detailed observations have not turned up nearly enough such objects to account for dark matter’s influence, as physicist Don Lincoln of the U.S. Department of Energy’s Fermilab previously wrote for Live Science.
The current leading contender for dark matter’s mantle is a hypothetical particle called a Weakly Interacting Massive Particle, or WIMP, which would behave sort of like a neutron except would be between 10 and 100 times heavier than a proton, as Lincoln wrote. Yet, this conjecture has only led to more questions.