When researchers from Yale University presented the results of their observations of the galaxy NGC1052-DF2 in March 2018, their work encountered a mixture of praise and criticism.
Their research indicated that the unusual galaxy contained little to no dark matter – the idea contradicts the existing theory of dark matter, which is why it attracted so much attention.
Pieter van Dokkum, a team led by the Sol Goldman family, a professor of astronomy at Yale University, has discovered another galaxy that does not contain dark matter – a discovery that supports its initial observations that dark matter actually does is separable from galaxies.
These findings may lead us to completely rethink previous assumptions about the formation of galaxies.
Although we can not see dark matter, it is believed to be a large part of the mass of our universe. Our galaxies consist of dark matter as well as "normal" matter such as stars and planets.
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The discovery of scientists from galaxies that contain little or no dark matter is unprecedented to them as a surprise.
"The fact that we see something completely new is fascinating," said Shany Danieli at the Keck Observatory, which first discovered galaxies two years ago. "No one knew there were such galaxies, and the best thing for an astronomy student in the world is to discover an object, be it a planet, a star or a galaxy nobody knew or thought about."
To get a closer look at the discovered galaxies, the research team tracked the movements of ten star clusters and allowed them to see how much mass was in each galaxy.
Unusually, they found that the galaxies contained only as much mass as the stars would normally have, which means that most likely only normal matter was present in the galaxy.
The second galaxy, which has been identified as having no dark matter, was named NGC 1052-DF4 – a discovery as exciting to researchers as the original discovery of DF2.
"This means that the chances of finding more of these galaxies are higher than previously thought, and since we have no good ideas on how these galaxies were formed, I hope these discoveries will inspire more scientists, to work on this puzzle. " Dokkum told the Keck Observatory.
Until recently, it was believed that galaxies could not form without dark matter – but Rita Wechsler of Stanford University said to National Geographic, "We need to rethink what a galaxy is."
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Both DF2 and DF4 belong to a relatively new class of galaxies called ultra-diffuse galaxies. According to the Keck Observatory, they are about the size of the Milky Way, but have far fewer stars, causing them to appear "fluffy" and "translucent," making them harder to observe.
Despite the lack of dark matter in these galaxies, their existence actually reinforces the theory of dark matter: it underpins the notion that dark matter is a substance that is not coupled to "normal" matter, and shows that both are independent can be found from each other.
The researchers emphasized their hope to continue exploring new galaxies and said, "We hope this will take us one step further to understand one of the greatest mysteries of our universe – the nature of dark matter."