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When Pieter van Dokkum discovered the galaxy NGC1052-DF2, he was “staring” and was amazed.
It was a galaxy about the size of the Milky Way, but unusually transparent.
“It was like a ghostly glow in the sky,” says Dokkum, a professor at Yale University in the United States.
The explanation of a study published in the journal Nature this Wednesday for this aspect of NGC1052-DF2 is that it should not have dark matter.
If this were true, it would be the first time that a galaxy of this type is discovered, composed only of ordinary matter.
Physicists believe that dark matter – which can not be seen because it does not reflect light – is essential to the structure of the Universe as we understand it.
The authors of the research published in Nature were not looking for a galaxy free of dark matter, but had proposed to observe ultradiffus galaxies closely.
These are similar in size to the spiral galaxies with which we are more familiar, but have fewer stars.
Copyright of the SCIENCE PHOTO LIBRARY imageImage caption
This newly discovered “ghost” galaxy also has very few stars, but many of them are grouped in unusually bright clusters.
When the team of Dokkum, the main author of the article, studied the behavior of these clusters, they discovered that the entire mass of the galaxy seemed to be contained in these stars.
This is why there would be no room for dark matter.
The study in which this galaxy is described was carried out by scientists from the American universities of San José, in California, and Yale; of the Harvard-Smithsonian Center for Astrophysics; of the University of Toronto, and of the Max Planck Institute, in Germany.
The absence of dark matter is not something that happens in most galaxies.
” E n a galaxy h ay about five times more dark matter than regular matter , “said Michelle Collins, a physicist at the University of Surrey, UK, who was not involved in the study.
“As one moves away from the galaxy, there are fewer stars and more dark matter,” he added.
Dokkum, for his part, explains that the universe does not consist only of galaxies.
“In reality, the structure of the universe consists of the scaffolding of dark matter and everything else is stuck to it,” he says.