Galaxy without dark matter challenges scientific theories

Doug Carpenter
March 30, 2018

Many galaxies in the universe, included our own, have an estimate of roughly 30 times more dark matter compared to the normal matter as we know it. 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.

First identified with the Dragonfly Telephoto Array (DFA) and later observed by the Sloan Digital Sky Survey (SDSS), the NASA/ESA Hubble Space Telescope, the Gemini Observatory and the Keck Observatory, the galaxy without dark matter stunned scientists. "This thing is astonishing", said team member Pieter van Dokkum, "a huge blob that you can look through. It is literally a see-through galaxy", he added.

Yale University astronomer Pieter van Dokkum stumbled on the ancient galaxy that is "as big as the Milky Way but with only 1 percent of its stars", AP writes. They followed the motion of 10 star clusters to work out how much mass the galaxy had.

And the results were somewhat surprising; NGC 1052-DF2 contains at least 400 times less dark matter than astronomers predict for a galaxy of its mass, and possibly none at all. "To me, there are many ways that you could form a galaxy like this - for example, in a collision of other galaxies".

So, finding a galaxy with no dark matter raises the question: if the galaxy has no dark matter, how did it form?

Dark matter is the bedrock that all galaxies are anchored to.

In recent decades, astronomers have believed that invisible, mysterious dark matter is the dominant aspect of any galaxy. The ones in NGC 1052-DF2 are mysterious in and of themselves: Many are comparable in brightness to Omega Centauri, the single brightest globular cluster in the Milky Way. Dark matter seems to be needed to draw in sufficient material to form the galaxy and its stars, and halos of dark matter keep galaxies from spinning apart as they rotate.

"If there is any dark matter at all, it's very little", said van Dokkum in the press release. These clusters were found to be plodding along more slowly than expected, meaning there's far less mass in that galaxy than would be predicted.

If NGC 1052-DF2 behaves as the new research describes, he wrote, that presents challenges to both explanations for the missing mass in the universe. So how do astronomers know they exist?

Around 65 million light-years away, there's a galaxy which is called NGC1052-DF2 and which diminishes and diffuse. Yet in this odd galaxy, the projected signatures of these exotic effects are not seen.

These ideas, however, still do not explain how this galaxy formed. This study was published in Nature. "It looked like a diffuse blob sprinkled with very compact star clusters", said co-author Shany Danieli, a Yale graduate student. Because there's some regular issue right here, any kind of variation of customized gravity would certainly have that issue generate dark-matter-like impacts. It turns out that a galaxy without dark matter is incompatible with models that replace it using modified gravity. We only believe dark matter exists because we can see how it affects "regular", or baryonic, matter.

Dark matter and dark energy comprise the rest, and scientists have yet to directly observe either. NGC1052-DF2 disproves that theory, providing further evidence to the actual existence of dark matter. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope.

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