These five galaxies form a “celestial cluster”

The universe is basically a vast black void, illuminated here and there only by a twinkling cluster of stars. These galaxies are usually very far apart. For example, the Andromeda galaxy, the closest major neighbor of the Milky Way, is 2.5 million light-years away.

But there are exceptions. In 1982, Canadian astronomer Paul Hickson published a list of 100 compact groups of galaxies—usually a handful of seemingly quasi-impressive ones. One of those merged clusters was recently photographed by the Hubble Space Telescope, marking the space telescope’s 32nd anniversary.

The Hickson Compact Group 40 is located about 300 million light-years away in the constellation Watersnake. The five galaxies in the cluster lie in a region just 250,000 light-years across – twice the diameter of our Milky Way. X-ray telescopes have discovered that the galaxies are surrounded by a large cloud of extremely thin and hot gas. Astronomers believe there is also a lot of invisible dark matter in the cluster.

Because of their mutual attraction, the five galaxies will be closer together in the future. Eventually, they collide and merge into a giant elliptical galaxy. It is estimated that this will happen in about a billion years.

Incidentally, the Milky Way and the Andromeda galaxy are also pointing towards each other. The two large spiral galaxies have already joined the smaller Triangle galaxy. Together with dozens of dwarf galaxies, these three spirals form the so-called Local Group. It’s not particularly compact yet, but that will change in a few billion years.