Headlines > News > Picture of the Day - The cluster Abell 2744 consists mostly of invisible dark matter

Picture of the Day - The cluster Abell 2744 consists mostly of invisible dark matter

Published by Elina on Mon Sep 30, 2013 12:37 pm via: Space Telescope
Share
More share options
Tools
Tags

The bright galaxies make up less than 5% of the cluster’s mass, whilst rest is gas (around 20%), which is so hot that it shines only in X-rays, and dark matter (around 75%), which is completely invisible. Abell 2744, nicknamed Pandora’s Cluster, seems to be the result of a series of collisions over 350 million years of at least four separate galaxy clusters and its uniqueness lies in complicated and uneven distribution of the different types of matter. The location of dark matter was investigated through the exploitation of gravitational lensing, a phenomenon where light rays from distant galaxies bend whilst passing through the gravitational field present in the cluster, resulting in a series of tellate distortions in the images of galaxies. The plotting of the distortions’ pathways enables to map the location of mass and dark matter.

X-rays, dark matter and galaxies in cluster Abell 2744. Credit: NASA, ESA, J. Merten (Institute for Theoretical Astrophysics, Heidelberg/Astronomical Observatory of Bologna), and D. Coe (STScI)

X-rays, dark matter and galaxies in cluster Abell 2744. Credit: NASA, ESA, J. Merten (Institute for Theoretical Astrophysics, Heidelberg/Astronomical Observatory of Bologna), and D. Coe (STScI)

2 Comments
Doesn't the gravitational lensing assume that the object being viewed has had no velocity relative to general expansion? How can we make this assumption for these very old photons from those very distant galaxies?
Please explain in more detail what you mean with "velocity relative to general expansion"?
Photons don't change their velocity in vacuum. Neither through general expansion, nor through gravitational lensing. The former changes their wavelength.
Leave a reply
You must be logged in to post a comment.
© 2014 The International Space Fellowship, developed by Gabitasoft Interactive. All Rights Reserved.  Privacy Policy | Terms of Use