Hubble celebrates spooky season with Abell 611, a web of galaxies linked by a dark mystery

In celebration of Halloween, Hubble brings you an inky snapshot of the galaxy cluster Abell 611, which lies more than 1,000 megaparsecs, or about 3.2 billion light-years, from Earth. Like all galaxy clusters, the continued existence of Abell 611 is a mystery to astronomers.

In particular, it appears that the network of rapidly rotating galaxies does not have enough mass to prevent it cluster from will fly away. This is a well-established problem in astronomy with very massive structures like galaxies and galaxy clusters – they just don’t contain enough total mass to stay whole.

It is interesting that this problem does not present itself on a smaller cosmic scale. For example, the passage of the planets of the solar system around the sun can be calculated relatively easily using the masses and positions of the planets and the sun. No additional mass is needed to explain the integrity of the Solar System or other star-planetary systems. So why does this intuitive rule break down on a large scale?

A common theory is that the universe contains vast amounts of matter known as dark matter right. Although the name may sound ominous, “dark” simply refers to the fact that this unknown quantity does not seem to interact with light the way other matter does—not emitting, reflecting, or absorbing any part of the electromagnetic spectrum. This dark quality makes dark matter incredibly difficult to characterize, although various possibilities have been postulated.

Essentially, most dark matter candidates fall into one of two categories: particles of some type that exist in vast quantities throughout the universe but for some reason don’t interact with light like other particles; or some type of massive object that also exists in abundance throughout the universe but is undetectable with current telescope technology.

Two of the most whimsical names dark matter candidates belong to the first and second category, respectively. Weakly interact massive particles (WIMPs) are hypothetical subatomic particles that do not interact with photons – in other words, they do not interact with light. Massive Astrophysical Compact Halo Objects (MACHOs) are a hypothetical set of very massive objects made (unlike WIMPs) of a type of matter that we already know about, but which are very difficult to observe because they emit very little light .

However, despite enormous efforts, no conclusive evidence for the existence of WIMPs, MACHOs, or any other form of dark matter has been found.

While dark matter remains stubbornly undetectable, fortunately it can be easily quantified. in fact, galaxy clusters such as Abell 611 are ideal laboratories for quantifying dark matter due to the abundant evidence of gravitational lensing seen in the cluster. An example of lensing is perhaps most clearly visible in the center of the image, to the left of the cluster’s glowing core, where the light curve can be seen. This curve is light from a more distant source that has been bent and distorted (or “lensed”) by Abell 611’s massive mass.

The degree to which light has been bent by the cluster can be used to measure its true mass. This can then be compared to an estimate of its mass obtained from all visible components of the cluster. The difference between the calculated mass and the observed mass stunning. In fact, zooming out, astronomers now estimate that about 85% of the matter in the universe dark matter.

Even so far the mystery of what the cosmic web holds galaxy within Abell 611 together remains unsolved, we can still enjoy this image and the exciting science – both well-established and theorized – that takes place within it.