Dark matter is still a great mystery for astronomers and scientists. However, it is believed that the entire universe consists of some 85% dark matter. Scientists still can’t understand what it fully consists of and what is its purpose in the universe. However, just recently they observed a galaxy without dark matter, which brought even more confusion to them, given that dark matter makes up so much of the mass of the universe.
Many galaxies in the universe, included our own, have an estimate of roughly 30 times more dark matter compared to the normal matter as we know it. There are dwarf galaxies, believed to consist of 400 times more dark matter than normal, according to Newsweek. This galaxy without dark matter has never been observed before and it brings confusion to everything we’ve known about this invisible and odd thing that is so present in the cosmos.
The galaxy is located 63 million light-years away from our Milky Way. What scientists know about it is that it’s an elliptically shaped galaxy, which they have named NGC1052-DF2. Given that there isn’t a trace of the dark matter, data suggests that it’s made entirely of normal matter.
Scientists conducted a study on this, publishing their findings in the journal Nature. In the study, scientists measure mass by tracking the velocity of bodies that move inside the galaxy, Pieter van Dokkum, co-author of the study told Newsweek. His explanation could be applied in real-time as, if the sun was 4 times more massive than it is, our planet would need to move around it two times faster to remain in the same orbit. Observing the velocity of the bodies that move around their respective stars can determine the mass of the stars.
In this same way, the researchers observed this galaxy. They followed the motion of 10 star clusters to determine the mass of the galaxy. When they compared this mass and the mass of the visible stars in the galaxy and subtract their difference, they find out how much of the galactic mass is dark. However, there was no dark matter found in this galaxy.
The discovery of the galaxy without dark matter, according to van Dokkum, “was completely unexpected.” Previously, the team took a look at other galaxies with similar properties and the same class as NGC-1052-DF2, discovering that they almost entirely consisted of dark matter. “So finding the opposite, namely an absence of dark matter really came out of the blue for us,” he added.
As scientists found an entire lack of the mysterious dark matter, it paradoxically provides scientists with even more evidence that dark matter is real. There are several theories about dark matter. Some theories suggest that it’s just an illusion of scientists not understanding the exact way gravity works when applied to something as massive as the universe.
“In those theories, every galaxy should show a dark matter signature, as it’s not due to dark matter at all but due to the laws of physics,” van Dokkum explained.