We’ve all heard these phrases at least once. But when we do, we ask what exactly dark matter and dark energy are and why are they important? Unfortunately, even some of the smartest scientists who’ve studied the cosmos for decades don’t have a complete answer for these mysterious substances. Still, these same scientists keep saying they’re out there and they’re important. So, what exactly is dark matter and dark energy, and why are they important? Once again, we don’t have a complete answer, but we can hopefully provide some insights into these mysterious substances based on recent research and what other little information we do know.
As its name suggests, dark matter is a form of matter, though not the type we are all familiar with, known as normal matter. Normal matter comprises the Earth and everything observable in the cosmos. But it only makes up about 5 percent of the universe, with a larger portion composed of about 27 percent dark matter. Another suggestion from its name implies that dark matter is, indeed, dark, meaning we can’t see it, even if light interacts with it.
In contrast, we can observe black holes when light interacts with them, but dark matter is entirely different, making its detection difficult. Despite this, scientists have used models to hypothesize that some mysterious substance is responsible for galaxies behaving the way they do in terms of their formation and evolution, meaning dark matter could share a common trait with gravity. In essence, dark matter is the invisible “glue” that keeps everything together.
The term “dark matter” was first used in 1933 by Swiss astronomer Dr. Fritz Zwicky, who spent most of his career as a Professor of Astronomy at the California Institute of Technology. He came up with the term when trying to explain whatever unseen matter could be responsible for the behavior of the Coma Galaxy Cluster, consisting of thousands of galaxies whose total diameter spans 20 million light-years across. What Dr. Zwicky found unique about Coma was that the galaxies were all moving too rapidly, given their massive sizes, and he proposed dark matter being the explanation behind their strange velocities.
If normal matter comprises about 5 percent of the universe and dark matter comprises about 27 percent, where does the remaining 68 percent come from? This comes in the form of dark energy, which, like dark matter, scientists also know very little about, and there is still a myriad of hypotheses that attempt to explain both what it is and its purpose.
Dark energy was first discovered by observing supernovas in 1998 when astronomers attempted to ascertain the reasons why the universe’s expansion seemed to be accelerating, as opposed to slowing down as had been the longstanding hypothesis. This phenomenon was described as a sort of “anti-gravity” that pushed outward, as opposed to dark energy, which appeared to pull inward and keep everything together.
Recent research into dark matter involves using its “clumpiness” to better understand how its interactions with galaxies, along with an ancient galaxy, potentially not possessing dark matter, at all. For dark energy, a recent set of papers published in The Astrophysical Journal and The Astrophysical Journal Letters discussed black holes as being a potential origin of dark energy.
For now, dark matter and dark energy remain two of the biggest enigmas in science as we continue the quest to ascertain their origins, compositions, and purposes in our mysterious universe.
What new discoveries will scientists make about dark matter in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!
Sources: Wikipedia, Wikipedia (1), European Space Agency, NASA, NASA (1), U.S. Department of Energy, European Space Agency (1), Cosmos, NASA (2), Labroots, Labroots (1), The Astrophysical Journal, The Astrophysical Journal Letters, Vice