Galaxy without any dark matter baffles astronomers

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For comparison, astronomers have found that the Milky Way Galaxy has an amount of dark matter that's 30 times greater than all the matter we can see with our array of different telescopes.

In what appears to be a first, an global team of astronomers have found something amiss with a galaxy 65 million years away - a distinct lack of dark matter. It is also thought to be more abundant than regular matter, with dark matter making up 27 percent of the mass and energy of the universe compared to just 5 percent for the matter that we can see. To resolve the discrepancy, the team scrutinized the galaxy with the Hubble Space Telescope, the W.M. Keck Observatory and the Gemini Observatory, the latter two on Mauna Kea in Hawaii.

The galaxy, called NGC 1052-DF2, is about 65 million light years away. "It's so rare, particularly these days after so many years of Hubble, that you get an image of something and you say, 'I've never seen that before.' This thing is astonishing: a big blob that you can look through".

Van Dokkum said NGC1052-DF2 is so sparse that "it is literally a see-through galaxy". The newly discovered galaxy is about the volume and size of the Milky Way but has 200 times fewer stars.

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Look out into the universe, and we see an abundance of matter, in stars, planets, dust, nebulae and galaxies, but there's something even more abundant out there, that we can't see.

Every galaxy that has been spotted contained a dark matter signature.

There have been several ideas that have floated around regarding the true nature of dark matter, and discoveries like this will only push astronomers to unlocking its secrets. 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. That would only make sense if there was no dark matter at all acting on them, a finding confirmed when the researchers subsequently calculated the mass of the galaxy. When van Dokkum and his team found NGC 1052-DF2, they expected to see something similar. Astronomers know it's there because of its gravitational influence, but they can't detect it any other way. By measuring their motions, the astronomers could calculate the mass of material enclosed inside their orbits. He points out that the galaxy, memorably named NGC1052-DF2, is orbiting another one. Yet in this unusual galaxy, the projected signatures of these exotic effects are not seen. "So finding the opposite, namely an absence of dark matter, really came out of the blue for us", he said.

Stacy McGaugh, an astrophysicist at Case Western Reserve University in OH who has worked on both dark matter and MOND and did not work on the paper, disagreed with the idea that this galaxy refutes MOND or bolsters the case for dark matter.

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Speculative explanations include that a collision or cataclysmic event within the galaxy resulted in all the dark matter being swept away. This large, fuzzy-looking galaxy is so diffuse that astronomers can clearly see distant galaxies behind it.

These ideas, however, still do not explain how this galaxy formed. Already have suspicions of three, whom they will notice better. The discovery provided more clues into how dark matter works.

"Paradoxically, the presence of NGC1052- DF2 might misstate options to dark issue", the writers end, keeping in mind that those choices consist of both variants of MOND and also emergent gravity. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope.

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