Thu. May 26th, 2022

Dark matter is the invisible something galaxies glow together like cosmic duct tape. But a team of scientists says they have found a distant galaxy completely devoid of dark matter, a finding that could shake the understanding of both dark matter and galaxy formation.

Although we can not directly observe dark matter (physicists believe it makes up about 27% of the universe), we do see the effects of its gravity. When we look out into the cosmos, we see that all galaxies appear to have “extra” mass – they behave as if they contain much more matter than we can actually detect. In the latest case, however, a team of astrophysicists tried to observe the effects of dark matter on the gas rotating in a distant dwarf galaxy, but they found that normal matter alone could explain the motion of the gas. There was no room for dark matter as far as they could see. The team’s research has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

Filippo Fraternali, an astrophysicist at the University of Groningen in the Netherlands and a co-author of the paper, told Gizmodo in an email that the galaxy that the team studied could only be held together by its visible mass – which sounds quite reasonable, except that dark matter is thought to be an important ingredient in all galaxies. “The main problem is that in our scenario of galaxy formation, galaxies cannot form without dark matter, and even more, dwarf galaxies should have large amounts of it,” Fraternali said. “Therefore, there is something we do not understand.”

The galaxy is called AGC 114905 and is about 250 million light-years from Earth. It is ultra-diffuse, meaning that its substance is spread over a large space; AGC 114905 is about the size of the Milky Way, but has about 1,000 times fewer stars. The research team used the National Radio Astronomy Observatory’s Very Large Array Telescope to look at the rotation of gas in the galaxy over 40 hours, ranging from July to October 2020.

The results are similar to those of NGC1052-DF2, another dwarf galaxy apparently lacking dark matter, which was described in 2018. Quite quickly, a controversy erupted over the claim; some astrophysicists believed that the galaxy was evidence of a new type of galactic growth, while others believed that it was misinterpreted and that the team needed more data. That a galaxy simply could not have any dark matter was a rather shocking claim.

Recently, a team double-checked the measurements on NGC1052-DF2, which seemed to confirm what the original team had found regarding the distance of the galaxy and thus the content of dark matter. Nicolas Martin, an astronomer at the Max Planck Institute for Astronomy, told Gizmodo at the time that the galaxy “may have had an unexpected formation and evolution”, and “the good thing is that future telescopes and studies will make it easier to understand NGC1052-DF2. and to put meaningful limits on how peculiar it is. In other words, is this system extremely rare, or is it part of a larger population that at present cannot be easily explained by galaxy formation models? ” Now, with the discovery of AGC 114905, there is more evidence that there is actually a population galaxy that just cannot be explained with current models.

The latest team found that the dark matter halo of AGC 114905 – the footprint of dark matter in and around a galaxy – had to consist of virtually (if not completely) no dark matter to match the data they collected. One explanation for the absence was that the galaxy had been deprived of its dark matter by large galaxies nearby – except that there were no such galaxies around it.

“Theory predicts that there must be dark matter in AGC 114905, but our observations say it is not,” said Pavel Mancera PiƱa, an astrophysicist at the University of Groningen in the Netherlands and lead author of the paper, in a Royal Astronomical Society press release. . “In fact, the difference between theory and observation only gets bigger.”

Another theory was that the angle at which the team observed the galaxy made the dark matter difficult to see, but co-author Tom Oosterloo, an astrophysicist at the Dutch Institute of Radio Astronomy, noted in the same publication that the actual angle would be beautiful. extreme in relation to the team estimate.

The team is currently investigating another ultra-diffuse galaxy to see if it is also unlikely to be missing in the dark matter department. If so, it will support the team’s analysis of the first galaxy. Observations are now underway and Fraternali said the team expects similar data. The more we learn about it, the more enigmatic dark matter seems to become.

More: What is dark matter, and why has no one found it yet?

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