From Ethan Siegel: “Hubble Views The Final Frontier For Dark Matter”

Ethan Siegel
May 8, 2017

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The streaks and arcs present in Abell 370, a distant galaxy cluster some 5-6 billion light years away, are some of the strongest evidence for gravitational lensing and dark matter that we have. NASA, ESA/Hubble, HST Frontier Fields

When you look out into the distant Universe, in most locations, you’ll find a field of faint, distant galaxies: beautiful, but nothing special.

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The ‘parallel field’ of Abell 370 showcases a deep view of a region of space with no particularly massive or significant structure inside. This is what most of the Universe looks like, when imaged deeply enough. NASA, ESA/Hubble, HST Frontier Fields

Six billion light years away, Abell 370 is one of the most massive, dense ones discovered so far, but one galaxy, noticed early on, provided a hint of something more.

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The distorted galaxy shown here is actually two images of a single galaxy located twice as far away as the rest of the galaxy; it is the effects of gravitational lensing that cause the odd appearance and multiple images. NASA, ESA/Hubble, HST Frontier Fields

The “stretched-out” galaxy you see here isn’t a distorted cluster member, but is instead two images of a single galaxy, twice as far away as the cluster itself.

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An illustration of gravitational lensing showcases how background galaxies — or any light path — is distorted by the presence of an intervening mass, such as a foreground galaxy cluster. NASA/ESA

This phenomenon of gravitational lensing stretches galaxies into streaks and arcs, magnifying them, and creating multiple images.

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The streaks of galaxies shown here are not representative of the actual shapes of the galaxies themselves, but rather the galaxies subject to the effects of the gravitational lens they pass through. Undistorted galaxies, like the one at the top left, are most likely in the foreground of the lens. NASA, ESA/Hubble, HST Frontier Fields

It also enables us to reconstruct the mass distribution of the cluster, revealing that it’s mostly due to dark matter.

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The mass distribution of cluster Abell 370. reconstructed through gravitational lensing, shows two large, diffuse halos of mass, consistent with dark matter with two merging clusters to create what we see here. NASA, ESA, D. Harvey (École Polytechnique Fédérale de Lausanne, Switzerland), R. Massey (Durham University, UK), the Hubble SM4 ERO Team and ST-ECF

There are two separate clumps present, showing that this is likely two clusters merging together.

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Despite the presence of large, elliptical galaxies, the location where the mass density is greatest, indicated by the dotted circle, corresponds to no known massive galaxy or other structure based in normal matter. The only explanation for this is the presence of an invisible source of mass: dark matter. NASA, ESA/Hubble, HST Frontier Fields / E. Siegel (annotation)

Most importantly, dark matter must be present — and present outside of the individual galaxies themselves — to explain these gravitational effects.

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A 2009 image, based on only a fraction of the Hubble data available today, revealed some of the incredible structure in Abell 370. The current data, benefitting from 8 extra years, showcases even more information about the distant, massive Universe. NASA/ESA Hubble

Additional observations from 2009-2017 reveal unprecedented details about the massive, distant Universe.

See the full article here .

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“Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

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