Sci-tech

In a galaxy far, far away, Dark Matter appears to be missing

In a galaxy far, far away, Dark Matter appears to be missing

Its presence is instead inferred through the gravitational pull it exerts on any normal matter around it. Astrophysicists think dark matter's gravity is crucial for forming the universe's large-scale structure of filaments and sheets of galaxy clusters, and scientists have even measured how clumps of it act as gravitational lenses, magnifying light from far-distant background galaxies.

Since dark matter was (sort of) discovered, researchers assumed dark matter was essential to galaxy formation.

"Finding a galaxy without dark matter is unexpected, because this invisible mysterious substance is the most dominant aspect of a galaxy", said Dokuum.

Scientists now think that dark matter is essential to the fabric of the universe.

So, finding a galaxy with no dark matter raises the question: if the galaxy has no dark matter, how did it form? "It's the glue that holds the visible matter in galaxies - stars and gas - together", it explained, in a statement on the discovery.

The scientists spotted NGC1052-DF2 using the Dragonfly Telephoto Array, a telescope in New Mexico. Further study of those clusters found that the stars appear to account for the entire mass of the galaxy.

Paradoxically, the authors said the discovery of a galaxy without dark matter counts as evidence that it probably does exist.

This galaxy, NGC 1052-DF2, is the size of the Milky Way but only has 1/200 the amount of stars, with no dense center or spiral arms or black hole.

But if dark matter is real, physicists still have to explain how the stars of NGC 1052-DF2 got separated from it.

Speculative explanations include that a collision or cataclysmic event within the galaxy resulted in all the dark matter being swept away.

Indeed, over the last few years Dokkum and Abraham have used it to uncover a whole new category of sparsely populated "ultra diffuse galaxies" - and sparked a cottage industry as astronomers struggle to explain their unusual properties. The visible mass was essentially the same as the total mass of the galaxy.

The researchers next used NASA's Hubble Space Telescope and the Gemini Observatory in Hawaii to uncover more details about the unique galaxy. The galaxy was then renamed NGC1052-DF2. They discovered this by watching smaller collections of stars, known as globular clusters, orbit the galaxy. This is not observed in NGC 1052-DF2, which resides about 65 million light-years away in the NGC 1052 Group, which is dominated by a massive elliptical galaxy called NGC 1052. What scientists know about it is that it's an elliptically shaped galaxy, which they have named NGC1052-DF2. After that everything else happens: gas falls into the dark matter halos, the gas turns into stars, they slowly build up, then you end up with galaxies like the Milky Way. Mysterious "dark matter" makes up the rest. "We know so little about dark matter that any new constraint is welcome", says van Dokkum. It's so sparse that you see all of the galaxies behind it. In another, an huge galaxy that's relatively close to DF2 may have somehow influenced the smaller galaxy during its formation. "It is completely unknown how it is possible to form such a galaxy". However, if that was the case, DF2 would exhibit the exact same abundance of dark matter that all other galaxies - even other Ultra-Diffuse Galaxies - appear to have. 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.


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