Astronomers just found a second galaxy containing no dark matter – and it may change everything we knew about how galaxies are formed - Business Insider

Twin Galaxies While we can't see dark matter, it's thought to make up a large part of our universe's mass.Gemini Image Gallery

When researchers at Yale University claimed to have discovered a galaxy containing no dark matter in March 2018, their work was met with a mixture of praise and criticism.
Much of the criticism the discovery received was down to the fact that it completely contradicts existing dark matter theory.
However, scientists recently made an exciting discovery — they found yet another galaxy that appears to contain only "normal" matter.

When researchers at Yale University presented the results for their observations of galaxy NGC1052-DF2 in March 2018, their work was met with a mixture of praise and criticism.

Their research suggested that the unusual galaxy contained little to no dark matter — the idea contradicts existing dark matter theory, which is part of the reason why it drew so much attention.

However, a team led by Sol Goldman Family Professor of Astronomy at Yale University, Pieter van Dokkum, has discovered yet another galaxy that doesn't contain any dark matter — a discovery that supports their initial observations that dark matter is actually separable from galaxies.

These findings may require us to totally rethink previously held assumptions about how galaxies are formed.

While we can't see dark matter, it's thought to make up a large part of our universe's mass. Our galaxies consist of dark matter as well as "normal" matter like stars and planets, for example.

The scientists' discovery of galaxies that contain little to no dark matter is unprecedented and came to them as somewhat of a surprise.

"The fact that we're seeing something that's just completely new is what's so fascinating," said Shany Danieli in Keck Observatory, who first spotted the galaxies two years ago. "No one knew that such galaxies existed, and the best thing in the world for an astronomy student is to discover an object, whether it's a planet, a star, or a galaxy, that no one knew about or even thought about."

In order to take a closer look at the discovered galaxies, the research team followed the movements of ten star clusters, allowing them to ascertain how much mass was in each galaxy.

Unusually, they found the galaxies contained only as much mass as the stars would normally have had, meaning that — most likely — there was probably only normal matter present in the galaxy.

The second galaxy found to be absent of dark matter has been dubbed NGC 1052-DF4 — a discovery that's just as exciting for the researchers as the original discovery of DF2.

"This means the chances of finding more of these galaxies are now higher than we previously thought. Since we have no good ideas for how these galaxies were formed, I hope these discoveries will encourage more scientists to work on this puzzle," Dokkum told the Keck Observatory.

Up until recently, it was thought that galaxies couldn't form without dark matter — but Rita Wechsler of Stanford University said to National Geographic, "We need to rethink what a galaxy is."

Both DF2 and DF4 belong to a relatively new class of galaxies called ultra-diffuse galaxies. According to Keck Observatory, they're roughly the same size as the Milky Way but have far fewer stars, which causes them to appear "fluffy" and "translucent", making them harder to observe.

Despite the lack of dark matter in these galaxies, their existence actually further bolsters the dark matter theory: it backs up the idea that dark matter is a substance not coupled to "normal" matter, and shows they can both be found independent of one another.

The researchers highlighted their hope to continue exploring new galaxies, saying: "Our hope is that this will take us one step further in understanding one of the biggest mysteries in our universe – the nature of dark matter."

Den Originalartikel gibt es auf Business Insider Deutschland. This post originally appeared on Business Insider Deutschland and has been translated from German. Copyright 2019. Und ihr könnt Business Insider Deutschland auf Twitter folgen.

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