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Astronomers perplexed to find that distant galaxy has no dark matter

29 March 2018

So-called dark matter is as much a defining feature of galaxies as stars and gas, and is thought to provide the gravitational seeds from which galaxies assemble and grow. It is filled bright galaxies of all shapes and sizes and lots dark matter, but yet these faint galaxies were sprinkled throughout. Finding such a thing would be like finding smoke but no fire, effect without cause.

"For decades, we thought that galaxies start their lives as blobs of dark matter", said Yale University astronomer Pieter van Dokkum, lead author of the study, in a press release.

The newly discovered galaxy is called NGC1052-DF2, or DF2 for short. It is nearly as big as the Milky Way but is "ultra-diffuse", meaning it contains just a vanishing fraction of the stars found in our galaxy-only 1 percent, in this case. It does not look like a typical spiral galaxy, but it does not look like an elliptical galaxy either. "Dark matter accumulates; ordinary gas falls into it; it turns into stars, and then you get a galaxy", says astrophysicist Jeremiah Ostriker of Columbia University, who was not involved in the work.

While NGC 1052-DF2 doesn't break any fundamental rules of the dark matter theory, Bauer said the galaxy is surprising and unexpected enough to force astrophysicists to develop some new models of how galaxies come together.

Dark matter is the bedrock that all galaxies are anchored to. The main component of galaxies is the mysterious dark matter.

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Theories like modified Newtonian dynamics and a new idea called emergent gravity propose that there is no dark matter. "It's a problem for nearly every theory that's out there".

He said: "Something like this has never been seen". "The standard paradigm has gas falling into halos - or lumps - of dark matter and turning into stars to make a galaxy", he said. Normally, we infer that there's dark matter around because the galaxy appears to have a lot more matter than the amount provided by the stars we can see.

The weird object was first spotted by astronomers using the Dragonfly Telephoto Array, a special 48-lens telescope in New Mexico, US, created to find ultra-diffuse galaxies.

Based on the ratio in other galaxies, an isolated galaxy like NGC1052-DF2 should have about a hundred times more dark matter than ordinary matter. So when van Dokkum and his team found NGC1052-DF2, they expected to see something similar. They found that dark matter is either very sparse or isn't there at all.

The scientists apparently expect the kind of inquiries that will certainly be presented by individuals that see this and also ask yourself why we require any kind of dark issue around anyhow (a populace that consists of a variety of routine Ars visitors). And van Dokkum adds: "This invisible, mysterious substance is by far the most dominant aspect of any galaxy". Dragonfly saw it as a scattered things with some frameworks in it; Sloan imaged it as a collection of unique things.

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Van Dokkum and his team used Keck telescopes in Hawaii and identified 10 globular clusters which are large compact groups of stars that orbit the galactic core. Gemini revealed that the galaxy does not show signs of an interaction with another galaxy; Hubble helped to identify the globular clusters and measure an accurate distance to the galaxy. The researchers then set about measuring the movements of the clusters as a way to estimate the galaxy's total mass.

Dark matter also connects giant clusters of galaxies with thin tendrils, forming an enormous cosmic web that gives the universe its structure. And surprisingly, it's about the same amount of mass they'd expect to see from the galaxy's stars alone.

None of these speculative hypotheses are able to explain all the galaxy's peculiarities, though.

Prof Jeremiah Ostriker, a professor of astronomy at Columbia University in NY, described the observation as highly significant. However, even the globular clusters are odd: they are twice as large as typical groups of stars. "The key thing is to see whether the globular clusters really are tracing the mass of the galaxy as a whole". They realized that it is about equal to the sum of masses of the stars, gas and dust that constitute it. Logic? This would allow the gas to form stars away from clumps of dark matter. "There must be more than one way to form galaxies". "What we found is that there is no dark matter at all".

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Astronomers perplexed to find that distant galaxy has no dark matter