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Dark thing is weird and frustrating. We've never seen it, since 1 of its properties is that it doesn't interact with normal affair or with electromagnetic radiation at either end of the spectrum. Current estimates suggest that dark matter is far more than common than ordinary thing, constituting between three-quarters and 84.5% of the total mass of the universe. In our own galaxy, night matter is thought to be almost five times more than mutual than ordinary matter – just now scientists working with the Gemini North and Keck Ii telescopes have discovered a galaxy that's made from 99.99% dark matter. And they noticed it because it was "fluffy."

This new galaxy, dubbed Dragonfly 44, isn't the commencement dark matter galaxy we've found, just the others have been comparatively tiny. Dragonfly 44, in contrast, is roughly the size of the Milky Style, but only 1% equally bright: similar a "wisp of deject" compared to our home galaxy. Sure, Dragonfly 44 has stars, but not very many of them. And they're in a loose, fluffy distribution. So why are the stars still hanging out and then shut together, when they're in a "dumbo, violent region of space" so likely to shake them downward for spare atoms?

In gild for the galaxy to agree together at all, night affair has to be gluing it together. Nothing else explains the speed of the stars that make upwards Dragonfly 44, in the confront of its relatively small observable mass. In fact, even in the central regions of the ultra-diffuse galaxy, where the few remaining visible stars are concentrated, nighttime affair accounts for an estimated 98% of the mass. This is an unusual finding in an otherwise normal galaxy. As report author Pieter van Dokkum told the Washington Post:

"If it'due south a very big or very large galaxy, you tin can castor information technology off and say, oh, that must be a rare thing," he said, "but well-nigh of the stars in the universe alive in galaxies this size."

"Nosotros thought that that ratio of matter to dark thing was something we understood. We thought the formation of stars was kind of related to how much night matter there is, and Dragonfly 44 kind of turns that idea on its caput," he continued. "Information technology means we don't understand, kind of fundamentally, how galaxy germination works."

The night milky way Dragonfly 44. The image on the left is a broad view of the galaxy taken with the Gemini North telescope using the Gemini Multi-Object Spectrograph (GMOS). The close-upward on the right is from the aforementioned very deep image, revealing the big, elongated galaxy, and halo of spherical clusters of stars effectually the galaxy's core, similar to the halo that surrounds our Galaxy Galaxy. Dragonfly 44 is very faint for its mass, and consists well-nigh entirely of dark matter. Credit: Pieter van Dokkum, Roberto Abraham, Gemini, Sloan Digital Sky Survey

The reason nosotros infer the existence of night affair in the start place, despite still not being able to observe it directly, is that our current understanding of physics demands the existence of something. Here's the trouble in a nutshell:  There'south far too much energy in the Galaxy and other galaxies to allow them to retain their present configurations if night affair doesn't exist. The mass of the visible objects within the galaxy (stars, planets, nebulas, etc) isn't nearly loftier enough to explain the speed at which the galaxy rotates. The rotational velocity of the Galaxy and other galaxies is so high that they'd fly apart if the only matter belongings them together was the mass of the observable universe. Except, of course, they don't fly autonomously – which means something else is contributing mass and holding things together. Decades of analysis has demonstrated that dark matter exists – we see evidence of it in gravitational lensing (the way light bends in the presence of a strong gravitational field), and in measurements of cosmic background radiation.

The team is hoping to find new examples of dark matter galaxies closer to habitation. I of the predictions about dark affair is that when particles of dark thing (weakly interacting massive particles, or WIMPs) interact with each other, tiny flashes of ultraviolet lite are produced. In a typical galaxy, these are drowned out by the light of stars and stellar events. In a true dark matter galaxy, however, things might just be dark enough to make them out – at least if the galaxy is sufficiently shut to Globe.

Dragonfly 44 is named for Dragonfly, an assortment of sensitive telephoto lenses that van Dokkum and several other colleagues assembled for use as an unconventional if effective telescope. The area of space where the galaxy lies is known as the Coma galaxy cluster and it'south an estimated 330 meg light years away. 47 similarly faint galaxies were observed, far dimmer than the other galaxies within the cluster.

How these galaxies class is withal a mystery. Nature reports that a quasar at the heart of the milky way may have destroyed the gas reserves that normally would've formed conventional stars, or that interactions with other galaxies in the Coma cluster might be responsible for the phenomena. Either fashion, it's a highly unusual find that might 1 24-hour interval aid us empathize more about the material that constitutes much of the universe.

Read the full study at: http://arxiv.org/abs/1606.06291