How looking at a single, distant galaxy cluster can show us the invisible mass filling our space like nothing else.
“We find them smaller and fainter, in constantly increasing numbers, and we know that we are reaching into space, farther and farther, until, with the faintest nebulae that can be detected with the greatest telescopes, we arrive at the frontier of the known universe.” –Edwin Hubble
When you look out into the distant Universe, in most locations, you’ll find a field of faint, distant galaxies: beautiful, but nothing special.
However, in a few select locations, you’ll find massive clusters of galaxies, containing hundreds or even thousands of galaxies the size of the Milky Way and up.
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.
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.
This phenomenon of gravitational lensing stretches galaxies into streaks and arcs, magnifying them, and creating multiple images.
It also enables us to reconstruct the mass distribution of the cluster, revealing that it’s mostly due to dark matter.
There are two separate clumps present, showing that this is likely two clusters merging together.
Most importantly, dark matter must be present — and present outside of the individual galaxies themselves — to explain these gravitational effects.
Additional observations from 2009–2017 reveal unprecedented details about the massive, distant Universe.
Mostly Mute Monday tells the scientific story of an astronomical object or phenomenon in pictures, visuals and no more than 200 words.