A Galaxy With No Dark Matter Is Stumping Scientists & It’s A Complete Curveball
Dark matter is everywhere. Or, well, we thought it was. Dark matter is virtually unobservable, but scientists theorize it is vital to the creation of galaxies, and that it makes up about 80 percent of the matter in our universe. And now a recent discovery from a Yale-led research team may help dramatically expand our evidence in favor of dark matter, which may sound a little strange, because its game-changing discovery is a galaxy that doesn't seem to have dark matter at all.
The team, led by Pieter van Dokkum, Yale’s Sol Goldman Family Professor of Astronomy, published its report for the study, called "A galaxy lacking dark matter," in the journal Nature Mar. 28. Van Dokkum told Yale student newspaper YaleNews that by discovering a galaxy lacking dark matter, which he described as an "invisible, mysterious substance," scientists may be able to confirm dark matter exists in other galaxies.
It was van Dokkum who created and built, along with study co-author Roberto Abraham of the University of Toronto, the Dragonfly Telephoto Array, the telescope the team used to locate the dark matter-less galaxy, according to YaleNews. Called NGC 1052-DF2, the galaxy "had been cataloged previously, but the researchers noticed it looked quite different in Dragonfly images," YaleNews reported. According to Space.com, van Dokkum previously led a team that discovered the galaxy Dragonfly 44, "which is composed almost entirely of dark matter."
Van Dokkum told YaleNews NGC 1052-DF2 is a "see-through galaxy," saying, "This thing is astonishing, a gigantic blob that you can look through. It’s so sparse that you see all of the galaxies behind it."
Study co-author Shany Danieli, a Yale graduate student, told YaleNews, "It looked like a diffuse blob sprinkled with very compact star clusters." Danieli credited the Dragonfly for allowing the researchers to see "faint structures that no one has even seen before."
"We thought that every galaxy had dark matter and that dark matter is how a galaxy begins," van Dokkum explained to YaleNews. "So finding a galaxy without it is unexpected. It challenges the standard ideas of how we think galaxies work, and it shows that dark matter is real. It has its own separate existence apart from other components of galaxies."
One reason researchers on the study concluded NGC 1052-DF2 lacks dark matter is because stars within the cluster are moving at less than 23,000 miles per hour — three times slower than stars move in galaxies containing dark matter, YaleNews reported.
Researchers also calculated NGC 1052-DF2's mass using motion measurements, and those measurements indicate that "[i]f there is any dark matter at all, it's very little," van Dokkum told YaleNews. "The stars in [NGC 1052-DF2] can account for all the mass, and there doesn't seem to be any room for dark matter."
The study's findings may also show that dark matter may not be present in the creation of all galaxies, which means it's possible there's more than one way for galaxies to form, van Dokkum added.
If the research from van Dokkum's team does end up proving dark matter exists, it will be the conclusion of a search that began in the early 1900s, according to Phys.org. The site reported on a study published in November 2017, which theorized that dark matter does not exist after researcher André Maeder, honorary professor in the Department of Astronomy in UNIGE's Faculty of Science, found that his mathematical model of the universe "predicts the accelerated expansion of the universe without having to factor in dark energy."
Whether NGC 1052-DF2 ends up leading us to a conclusion on dark matter or not, it's certainly a reminder that the truth is definitely out there.