NGC 1052-DF2, a galaxy with almost no dark matter has left scientists scrambling for answers for years. The galaxy has way less dark matter than it should and no scientific reason can provide a viable explanation.
Dark matter, which was discovered in the 1970s by astronomer Vera Rubin while measuring the spinning speed of galaxies, gets its name from the fact that it is almost invisible. The fact that it is not exposed to the electromagnetic force, and hence does not produce any light, makes it impossible to detect by our astronomical equipment, as opposed to conventional matter.
However, in galaxies and galaxy clusters, it might account for up to 90% of their total mass, enabling them to achieve tremendous rotational speeds even at the perimeter of the observable universe.
However, in 2018, scientists identified NGC 1052-DF2, also known as DF2, a galaxy that was classified as “ultra-diffuse” and had a deficiency in dark matter. Researchers estimated that it should have held 400 times the amount of dark matter that it really did. Some explanations have been proposed to explain this shortfall, including the galaxy’s distance from the Earth, which would be poorly judged, and the suction of dark matter from the galaxy by a more massive neighbor.
Three years later, the researchers published their findings in The Astrophysical Journal Letters on June 9, 2021, which were updated with additional information.
After originally assuming the existence of dark matter in 1933 when attempting to determine the mass of a galaxy cluster, Fritz Zwicky proved it thirty years later when Vera Rubin conducted her own research into the subject.
Indeed, the mass of galaxies may be determined in two distinct ways: either by their brightness, in which case it is referred to as luminous mass, or by their rotational speed, in which case it is referred to as dynamic mass. However, the researchers noticed a discrepancy between the two masses at the time: the galaxies were rotating too quickly for their mass to be explained just by the stars that made them up.
The conclusion reached at the time was that there is an undiscovered mass source, which has subsequently been dubbed “dark matter.” The existence of dark matter has since been proven by a slew of discoveries, beginning with the discovery of galaxies and galaxy clusters and continuing through time.
Dark matter would account for 27 percent of our universe’s total mass, about six times the amount of conventional matter, which accounts for just 5 percent… It is believed that the remaining portion of the Universe is made up of dark energy, a mysterious substance that would explain the pace of expansion of the Universe and equate to a repulsive gravitational pull.
The rotational speed of the galaxy was initially measured three years ago, utilizing the motions of a dozen globular clusters on the galaxy’s periphery to determine the galaxy’s dark matter deficiency. The researchers then calculated the galaxy’s dark matter deficit. It is through measuring the speed of spin of the stars that scientists were able to determine that DF2 has a low mass, a mass that can be explained exclusively by the stars it contains, leaving no place for dark matter.
Pieter van Dokkum, an astronomer at Yale University who headed the study team in 2018, states: “If there is dark matter, it is in a very tiny proportion. All of the mass seems to be accounted for by the stars of the galaxy; there does not appear to be any room for dark matter.”
In addition to its lack of dark matter, DF2 exhibits a number of additional characteristics, the most notable of which is its transparency. “It is incredible: a massive hole through which you can peer. It is so sparse that you can see all of the galaxies in the background. In fact, it is really a translucent galaxy,” van Dokkum said further.
DF2 also does not include a core black hole, and the globular clusters that it contains are twice as huge as the star clusters seen in other galaxies, indicating that it is a more massive galaxy. “In a way, it is like if you take a galaxy and you just have the stellar halo and globular clusters, and you have completely forgotten about the rest of it. The existence of these sorts of galaxies cannot be anticipated by any hypothesis. Because everything in the cosmos is odd, the galaxy is a total mystery to us. It is totally unclear how you intend to train any of these creatures,” the researcher added.
Following the discovery of this galaxy, a number of ideas were put up to try to explain it. Because DF2 is located near a huge elliptical galaxy, NGC 1052, the latter may have “sucked” some of the dark matter from DF2 during its development, or it may have had a part in DF2’s dark matter deficiency in some way.
Another notion was that the gas traveling towards the gigantic NGC 1052 was responsible for the birth of the galaxy DF2 and its companion galaxy.
However, according to the researchers, no matter what explanation is put forth, it is unable to account for all of the observable properties of the galaxy.