Hubble celebrates the spooky season with Abell 611, a cobweb of galaxies held together by a dark secret

In celebration of Halloween, Hubble brings you this inky picture of the galaxy cluster Abell 611, positioned over 1000 megaparsecs, or roughly 3.2 billion mild years, from Earth. Like all galaxy clusters, the continued existence of Abell 611 poses a thriller to astronomers.

Particularly, there doesn’t seem like sufficient mass contained inside its internet of quickly rotating constituent galaxies to stop the cluster from flying aside. It is a well-established problem in astronomy with very huge constructions, akin to galaxies and galaxy clusters—they simply don’t appear to comprise sufficient mixed mass to stay entire.

Apparently, this downside doesn’t current itself on smaller cosmic scales. For instance, the passage of the planets of the solar system across the sun could be calculated comparatively simply utilizing the lots and areas of the planets and the sun. No further mass is required to clarify the integrity of the solar system, or different star-planet programs. So why does this intuitive rule break down at bigger scales?

The prevalent principle is that the universe comprises huge quantities of a substance referred to as darkish matter. While the title may sound ominous, “darkish” merely refers to the truth that this unknown amount doesn’t appear to work together with mild as different matter does—neither emitting nor reflecting nor absorbing any a part of the electromagnetic spectrum. This darkish high quality makes dark matter extremely tough to characterize, though numerous prospects have been postulated.

Basically, most dark matter candidates fall into one among two classes: some sort of particle that exists in huge portions all through the universe, however for some motive doesn’t work together with mild as different particles do; or some sort of huge object the additionally exists in nice abundance all through the universe, however doesn’t lend itself to detection utilizing present telescope expertise.

Two of probably the most whimsically named dark matter candidates fall into the primary and second class respectively. Weakly interacting massive particles (WIMPs) are hypothetical subatomic particles that don’t work together with photons—in different phrases, they don’t work together with mild. Large astrophysical compact halo objects (MACHOs) are a hypothetical set of very huge objects made (not like WIMPs) of a sort of matter that we already know of, however which might be extraordinarily exhausting to watch as they emit so little mild.

Regardless of great effort, nonetheless, no conclusive proof has been discovered of WIMPs, MACHOs, or every other type of dark matter.

If dark matter stays stubbornly undefinable, luckily it’s readily quantifiable. Actually, galaxy clusters akin to Abell 611 are excellent laboratories for the quantification of dark matter, owing to the ample proof of gravitational lensing seen throughout the cluster. An instance of lensing is maybe most clearly seen within the heart of the picture, to the left of the cluster’s glowing core, the place a curve of sunshine could be seen. This curve is mild from a extra distant supply that has been bent and distorted (or “lensed”) by Abell 611’s huge mass.

The extent to which mild has been bent by the cluster can be utilized to measure its true mass. This will then be in contrast with an estimate of its mass derived from all of the seen elements of the cluster. The distinction between the calculated mass and the noticed mass is staggering. Actually, zooming out, astronomers presently estimate that roughly 85% of the matter within the universe is dark matter.

Even whereas the thriller of what holds the cosmic cobweb of galaxies inside Abell 611 collectively stays unsolved, we are able to nonetheless get pleasure from this picture and the fascinating science—each effectively established and theorized—going down inside it.