The problem of galaxies without dark matter arose a few years ago, when the team led by Pavel Mancera Piña, an astronomer at the University of Groningen in the Netherlands, published a study on the measurements of the following galaxies: AGC 114905 AGC 122966 AGC 219533 AGC 248945 AGC 334315 AGC 749290 In the study, they said that all measurements of size, mass, and baryonic matter (common) in these galaxies dispensed with the presence of dark matter to hold them together. It turns out that this left the scientific community "hair-on-up" because current models predict that every galaxy needs dark matter to form.
So, Piña's team was told to remeasure their samples, and they would find the dark matter in them. That's what they did. They chose one of the closest to Earth, AGC 114905, located 250 million light-years away and almost as large as the Milky Way. Despite its size, AGC 114905 has a thousand times fewer stars than our Milky Way. This means that it is an ultra-diffuse galaxy with much more dispersed stars. The new measurements were taken during 40 hours of observation on the Very Large Array (VLA), one of the most powerful radio telescopes on the planet.
Absence of dark matter Observations of the diffuse galaxy AGC 114905 suggest that it has no dark matter (Image: Reproduction/Javier Román/Pavel Mancera Piña) With the new study, the evidence for the absence of dark matter in the galaxy has only increased. They made a graph showing the gas's distance from the center of the galaxy on the x-axis, and the gas's rotational speed on the y-axis — the standard way of detecting the presence of dark matter. The team's graph shows that the gas movements in AGC 114905 can be completely explained by baryonic matter alone. This is something that models cannot explain, because theoretically no galaxy remains without dark matter. “Actually, the difference between theory and observation is just getting bigger,” Piña said.
One of the possible explanations is that the tilt of the galaxy estimated by the authors is wrong. "But that angle has to deviate a lot from our estimate before there's room for dark matter," said co-author Tom Oosterloo (ASTRON). The researchers are examining another ultra-diffuse galaxy, and if there is no sign of dark matter in it either, the case will become even more troublesome and astronomers will be "forced" to rethink theories or explain how these galaxies have become an exception. .
Other galaxies without dark matter There are other cases of galaxies like this one, found around the same time as the first study published by Piña's team. One such case was presented by Yale University researcher Pieter van Dokkum in 2018. Another research was published by a Chinese team in 2019. Van Dokkum's galaxy is NGC 1052-DF4, a case that took a turnaround in 2020, with one study suggesting that van Dokkun's team's measurements were wrong. In June 2021, this hypothesis was refuted and the distances confirmed. The China team found no fewer than 19 galaxies without dark matter, or losing dark matter for some reason that is still unknown. Suspicions are that they may have been born different, or something has altered their internal structures, like exploding stars
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