The team of astronomers from Yale University claims that they found another galaxy that contains little to no dark matter.
In a study, the researchers presented NGC 1052-DF4 (or DF4), an ultra-diffuse galaxy. The discovery of DF4 is an undeniable proof that galaxies with little to no dark matter exist, altering the current understanding of how galaxies are formed and the mysterious stuff that makes up about 85 percent of the known universe.
Revisiting Galaxy DF2
Two years ago, the same team from Yale University presented their discovery of NGC 1052-DF2 or DF2, the first known galaxy with little to no dark matter. The discovery was met with both praise and skepticism from the scientific community.
While dark matter is still shrouded with mystery, scientists believe that the stuff is integral to the formation of galaxies and explains why some galaxies behave in a certain way. Some galaxies even have more dark matter than regular matter.
Now, the team has presented not one, but two studies that prove that DF2 has little to no dark matter and more similar galaxies exist across the universe.
In one study that appears in The Astrophysical Journal Letters, the astronomers took another look at DF2. The W. M. Keck Observatory's Keck Cosmic Web Imager allowed them to make precise measurements.
They confirmed that the globular clusters inside DF2 are moving at a speed consistent to the galaxy's normal matter. If dark matter was present, the globular clusters would move at a much faster speed.
A Second Galaxy With Little To No Dark Matter
The second paper, which was also published in The Astrophysical Journal Letters, is further proof that galaxies with little to no dark matter exist. In the study, the team used the W. M. Keck Observatory's Low Resolution Imaging Spectrometer (LRIS) to DF4 and found that similar to DF2, the galaxy is devoid of dark matter.
DF4 and DF2 are classified as ultra-diffuse galaxies, a relatively new class of galaxies that is about as large as the Milky Way but has significantly fewer (100 to 1,000 times less) stars. Both galaxies appear translucent and therefore difficult to observe.
"Discovering a second galaxy with very little to no dark matter is just as exciting as the initial discovery of DF2," stated Pieter van Dokkum, team leader and a professor of astronomy at Yale University. "This means the chances of finding more of these galaxies are now higher than we previously thought."
The researchers added that the discovery of DF2 and DF4 offer further evidence that supports the dark matter theory. It is proof that dark matter can exist separately from normal matter.
Astronomers are hoping to find out why the galaxies lack dark matter and how often they occur in the universe in their future studies.
"We want to find more evidence that will help us understand how the properties of these galaxies work with our current theories," said Shany Danieli, a graduate student at Yale University. "Our hope is that this will take us one step further in understanding one of the biggest mysteries in our universe — the nature of dark matter."