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, situated 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 look like sufficient mass contained inside its internet of quickly rotating constituent galaxies to forestall the cluster from flying aside. This can be a well-established problem in astronomy with very huge buildings, reminiscent of galaxies and galaxy clusters—they simply don’t appear to include sufficient mixed mass to stay entire.

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

The prevalent idea is that the universe comprises huge quantities of a substance generally known as darkish matter. While the identify 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 troublesome to characterize, though varied prospects have been postulated.

Basically, most dark matter candidates fall into one in every of two classes: some kind of particle that exists in huge portions all through the universe, however for some purpose doesn’t work together with mild as different particles do; or some kind 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 essentially 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 (in contrast to WIMPs) of a sort of matter that we already know of, however which can be extraordinarily onerous to watch as they emit so little mild.

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

If dark matter stays stubbornly undefinable, fortuitously it’s readily quantifiable. In reality, galaxy clusters reminiscent of Abell 611 are preferrred laboratories for the quantification of dark matter, owing to the plentiful proof of gravitational lensing seen inside the cluster. An instance of lensing is probably most clearly seen within the middle of the picture, to the left of the cluster’s glowing core, the place a curve of sunshine might 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 may then be in contrast with an estimate of its mass derived from all of the seen parts of the cluster. The distinction between the calculated mass and the noticed mass is staggering. In reality, zooming out, astronomers at the moment 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 will nonetheless take pleasure in this picture and the fascinating science—each nicely established and theorized—going down inside it.