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The galaxy without dark matter



The finding that DF2 apparently contains very little, if any, dark matter surprised researchers, because it is the first galaxy missing the penetrating material. "There is no theory that predicts these types of galaxies, the galaxy is a complete mystery because it's all weird about it," van Dokkum said. "How to actually form one of these things is completely unknown."

However, as so often before, the researchers have some ideas of how the galaxy originally formed. One possible scenario they point out in the paper is that DF2 is indeed a tidal dwarf galaxy. This type of galaxy can form during galactic mergers, which often emit baryonic material – ordinary matter consisting of protons, neutrons, and electrons. However, DF2 seems to have fewer metals than would be expected for a tidal dwarf galaxy. Another option is that the galaxy originated when winds from a nearby quasar swelled large clouds of low-metallicity gas, but researchers point out that the galaxy may be too diffuse to be a likely scenario. Finally, the researchers speculate that DF2 might have been formed when portions of gas flowing to NGC 1

052 broke off from the larger galaxy's black hole due to jet-induced shocks.

Regardless of how DF2 was formed, the team's findings show that dark matter is indeed a physical building block that can be separated from baryonic matter, and as a result, the results also question some of the alternative dark matter theories. One such theory is known as Modified Newtonian Dynamics (MOND), which aims to eliminate the need for dark matter by suggesting that gravitational force acts differently on low-acceleration objects such as those found on the outer edges of galaxies.

"This result represents a major challenge for MOND," said Yotam Cohen, student of astronomy at Yale and co-author of the study, on the Redshit website. "In MOND, the extra gravitational forces observed on galactic scales are woven into the equations, which means that wherever you see galaxies you can see the effect of modified gravity, but in this galaxy there is no need for the extra gravity to explain their kinematics – in other words, this suggests that galaxies and dark matter are separable components and that dark matter is a material substance, as the majority of professional astronomers think it. "

But before As astronomers can draw far-reaching conclusions about the true nature of our universe, the extraordinary findings of the study must first be verified and replicated. At this point, the team is already busy analyzing more Hubble images of dark and diffuse galaxies similar to DF2. "We currently have a sample of about 20 other low-surface-brightness galaxies identified with Dragonfly and subsequently traced with HST images," Cohen Astronomy reported by e-mail. "There are some of these objects that have similar brightness and structure to NGC1052-DF2, but none are so spectacular and none with so many star cluster candidates."

Although our current understanding has raised some of the recent challenges of dark matter – such as finding that satellite galaxies are organized and not random, as dark matter models predict – this is not necessarily a bad thing. Instead, it simply means that our current understanding of dark matter is not entirely correct. This should not be a complete surprise, as we have not yet found any direct evidence for the elusive material. Confusing results force scientists to consider a problem in several ways, which typically causes them to revise and update their theories so they can better describe the reality.

Isaac Asimov is probably the most exciting sentence in science "Eureka", but "hmm … that's weird."


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