In a New Hubble Picture, Darkish Matter Anchors the Big Galaxy Cluster Abell 611


Darkish matter. It’s secret. It’s darkish as a result of it doesn’t give off any mild. We are able to’t see it, style it, contact it, scent it, and even really feel it. However, astronomers can measure this darkish secret of the universe. How? By taking a look at galaxies and galaxy clusters. Darkish matter exerts a gravitational affect on these areas, and that CAN be measured.

Simply check out this picture of Abell 611. It’s a galaxy cluster that lies about 3.2 billion light-years away from us. At first look you assume, “yeah, it’s a cluster of galaxies, so what?” For astronomers although, this cluster poses a problem. They know from measuring it that there’s not sufficient mass within the galaxies and the cluster to maintain the entire thing from flying aside. Subsequently, gravity have to be holding it collectively. However, the place’s the “stuff” that has the gravitational affect? It’s not simply the stuff we are able to see within the galaxies. It should even be darkish matter.

The Cosmic Stuff that Confounds Understanding

The existence of galaxies and clusters that aren’t flying aside is a well known problem to astronomers, and never simply in Abell 611. Astronomer Vera Rubin and her workforce tackled the mismatch between a galaxy’s rotation charge and its mass again within the mid-Twentieth century. They noticed galaxies that appear to have extra mass than their rotation speeds would counsel. It wasn’t a brand new downside—astronomer Fritz Zwicky discovered Hubble’s observations of the Coma Cluster of galaxies puzzling again within the Nineteen Thirties. Some galaxies in that cluster look like shifting too quick and that ought to have blown the cluster aside. Zwicky puzzled over it and determined that some unknown factor he referred to as “dunkle Materie” (darkish matter) may clarify the anomaly.

In the present day, astronomers nonetheless grapple with understanding this cosmic “stuff.” Not simply because galaxy clusters aren’t flying aside. Or that galaxies aren’t both. It seems that the universe isn’t just stars and galaxies and nebulae and planets. About 85 % of the mass within the Universe is darkish matter. Evaluate that to the mass we are able to see—also called regular matter or baryonic matter. That contains solely about 5 %.

A simulation of dark matter distribution in the universe.
A pc simulation of the distribution of matter within the universe. Orange areas host galaxies; blue buildings are gasoline and darkish matter. Credit score: TNG Collaboration

So, we all know it’s there in most (however not all) galaxies. However what IS darkish matter? Quite a lot of theories abound, however they boil down to 2 potentialities. It could possibly be a sort of particle that exists everywhere in the Universe however doesn’t work together with mild. Or, it would include an in depth inhabitants of large objects that may’t be detected with our present know-how. So, they’re both WIMPs (weakly interacting large particles) or MACHOs (large astrophysical compact halo objects. Astronomers have seemed throughout for these items. Thus far, no credible detections exist, aside from to notice that no matter these items is, it’s holding galaxies and clusters from disintegrating.

Darkish Matter and Clusters

And, that brings us again to Abell 611. It’s truly a great check topic for the concept of darkish matter. Astronomers know that galaxies and clusters are dominated by their darkish matter parts. In Abell 611, the cluster’s look supplies proof for astronomers to measure the quantity of darkish matter there. Gravitational lensing, for instance, is the perfect seen proof. The curves of sunshine inside the cluster are literally photographs of extra distant galaxies whose mild is being distorted by gravity because it passes by means of. The mass of the galaxies within the cluster isn’t sufficient to make these distortions. So, one thing else must be doing it—and that might be darkish matter within the cluster.

SMACS cluster from JWST shows evidence of dark matter
The galaxy cluster SMACS 0723 as seen by NIRCam on JWST. Gravitational lensing properties (from its mass and from the mass of darkish matter) are serving to astronomers determine 88 distant galaxies on this area of view for additional examine. Courtesy NASA, ESA, CSA, STScI

In truth, clusters throughout the Universe present this impact of darkish matter haloes surrounding them. One in all JWST’s first photographs exhibits the gravitational lensing attributable to the halo across the cluster SMACS J0723.3-7327. It has hundreds of galaxies surrounded by a darkish matter halo. Every galaxy additionally has a part of darkish matter. The result’s the wonderful show of lensed galaxies seen within the picture. All of them lie at excessive distances behind the SMACS cluster, and their mild is smeared into arcs by the gravitational domination of the darkish matter. The truth that this similar scene performs out throughout many clusters all through the Universe tells us that darkish matter is actual, even when astronomers haven’t but found out what it’s.

For Extra Info

A Cosmic Cobweb
Darkish Power, Darkish Matter
Separating Galaxies from the Cluster Darkish Matter Halo in Abell 611

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