For the first time ever, scientists have identified a galaxy, NGC1052-DF2, that seems to lack the presence of dark matter. For decades, scientists have believed that dark matter is a major aspect of any galaxy, which makes this discovery completely baffling. In an odd way, the new galaxy’s lack of dark matter may serve as evidence for the existence of it by demonstrating that there is much astronomers do not understand about such vast low-density galaxies.
Although scientists have yet to directly observe dark matter, they believe it is out there due to the unusual motion of galaxies, which move as if under a greater gravitational force than that from the presence of regular matter. “These ultra-diffuse galaxies have a huge variety of properties,” study lead author Pieter van Dokkum told Gizmodo. “Some have a lot of dark matter, and some have no dark matter. There’s such an enormous range.” These observations have led scientists to believe that the universe may contain six times as much dark matter as ordinary matter. In a new study published in Nature, astronomers documented their observation that NGC1052-DF2 did not seem to rotate at all, indicating a lack of dark matter. “We could only derive an upper bound to the measured motion because it’s moving so slowly that our instrument couldn’t detect it,” said van Dokkum.
Related: Scientists capture first ever image of dark matter web that connects galaxies
The team also recently discovered a Dragonfly 44 with a similar structure to NGC1052-DF2, though its rotation suggests that the galaxy is composed of more than 99 percent dark matter. These observations were made possible by the Dragonfly Telephoto Array, a powerful telescope that shines a light on the universe’s secrets. This is exactly the sort of thing the Dragonfly instrument excels at discovering,” astrophysicist Sarah Tuttle told Gizmodo, “and confirming a low-mass galaxy without dark matter is an important step in understanding both galaxy formation and evolution, as well as cosmology.”
Images via Pieter van Dokkum and PBS
Dark matter fills 'empty' space, strongly interacts with visible matter and is displaced by visible matter. The reason for the 'missing dark matter' is that the galaxy is so diffuse that it doesn't displace the dark matter outward and away from the galaxy to the degree that the dark matter is able to push back and cause the stars far away from the galactic center to speed up. It's not that there is no dark matter connected to and neighboring the visible matter. It's that the galaxy is not well defined enough to displace the dark matter to such an extent that it forms a 'halo' around the galaxy. A galaxy's halo is not a clump of dark matter traveling with the galaxy. A galaxy's halo is the state of displacement of the dark matter.
Interesting article, Greg. I often wonder if what scientists refer to as "dark matter" is really some type of subatomic force that we have yet to understand. I'm not a physicist, but it's interesting to speculate.