Astronomers perplexed to find that distant galaxy has no dark matter

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Or, a cataclysmic event within DF2 such as an eruption of star formation could have cleared the galaxy of all its gas and dark matter.

Some scientists have been arguing in recent years that dark matter is not really there - that it's just a change in the laws of gravity that we don't understand.

Dark matter can't be seen or touched, but it outweighs all the normal matter in the universe by more than 5 to 1. It has its own separate existence apart from other components of galaxies. Data from observations made on this and other instruments around the world eliminated all other explanations but one: this galaxy did not interact with or have any dark matter.

"We thought that every galaxy had dark matter and that dark matter is how a galaxy begins".

Using Dragonfly, van Dokkum and colleagues found a large, sparse galaxy called NGC1052-DF2 in the northern constellation Cetus, also known as the whale.

Many scientists believe that dark matter - matter that scientists can not see directly - is everywhere in the universe, and helps explain how galaxies hold together.

A team of astronomers from the University of Toronto, Yale University, San Jose State University, University of California Observatories, the Harvard-Smithsonian Center for Astrophysics and the Max Planck Institute in Germany made the discovery. Or, van Dokkum speculates, perhaps this ultra-diffuse, dark-matter-free galaxy arose from two streams of gas that collided and compressed to form a scattering of stars. Which is pretty freakish.

When Prof Pieter van Dokkum, lead author of the study, first spotted NGC1052-DF2: "I stared a lot at that image and just marvelled at it..." Simply put, the velocity at which clusters orbit a galaxy is related to the amount of matter-normal or dark-that a galaxy contains.

A close-up of one of the globular clusters surrounding DF2. The astronomers speculate that the birth and formation of DF2 in the dynamic environment of the cluster could have been influenced by the giant galaxy.

The universe's ordinary matter includes things like gas, stars, black holes and planets, not to mention shoes, umbrellas, platypuses and whatever else you might see on Earth. Scientists believe it exists based on gravitational effects it seems to exert on galaxies. His stars are enough to explain his whole mass, and there seems to be no extra space for dark matter, "he added".

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The team also recently discovered a Dragonfly 44 with a similar structure to NGC1052-DF2, though its rotation suggests that the galaxy is composed of more than 99 percent dark matter.

So, DF2 is definitely an oddball.

In addition to providing insight into how galaxies form, the unusual galaxy is helping strengthen the argument for the existence of dark matter, researchers said. Most current narratives suggest that because dark matter dominates the universe, slightly denser patches of dark matter would have provided the initial seeds for things to clump together in the early universe and eventually end up as stars and galaxies. "Not sure what to make of it, but it is definitely intriguing", she said.

The galaxy was studied by many telescopes (Jemini and Kek Hawaii, Space Hubble, etc.) to cross-check the results.

The research team identified a few ways that DF2 may have formed. In another, an vast galaxy that's relatively close to DF2 may have somehow influenced the smaller galaxy during its formation.

That meant there was very little, if any, dark matter in this galaxy. Or did the growth of the nearby massive elliptical galaxy NGC 1052 billions of years ago play a role in NGC 1052-DF2's dark matter deficiency? They found that DF2 is about the size of the Milky Way but has about 200 times fewer stars. The stars only take shape on top of the dark matter that is already there.

What's next for this research?

Astronomers will be looking to find other galaxies in the universe.

"We're now undertaking a survey to find more objects like DF2", Abraham said.

"Conventional telescopes are good at finding small, faint objects".

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