Hubble immortalizes the extremely rare merger of three galaxies

⇧ [VIDÉO] You might also like this partner content (post ad)

Since its launch, Hubble has always fulfilled its role as a patient observer of the universe. And thanks to the Advanced Camera for Surveys (ACS), its ultra-precise third-generation camera, it has once again achieved a feat of more than 31 years of operation. Aimed at the constellation Cancer, the space telescope captured an extremely rare phenomenon: the epic merger of three large galaxies. Although collisions and mergers of galaxies have already been observed in the past, they more often concern pairs (and very rarely trios). To capture the dazzling merger, Hubble observed from a distance of about 681 million light years.

Given the galaxies’ impressive dimensions and the forces and energies involved, their merger can only be catastrophic, leaving “visible scars” millions of years later. The course of these mergers, spread over several million years, has already been simulated (by supercomputers) by astronomers. In particular, several research teams have tried to determine the course of the merger of our galaxy with the giant Andromeda (which will take place in about 4 billion years). Other researchers have seen traces of past mergers in our galaxy.

One could also think that these mergers only rarely occur in the universe. Yet it is a very common process in the evolution of a galaxy that helps create it. It should also be noted that merger and collision are different because the galaxies can still be separated by a collision. A less violent event than fusion, where more matter, gas and energy interact.

Also, according to the universal law of gravitation, one object is always attracted to another if it is more massive. The same principle is involved in galactic mergers. Thus, the galaxies inexorably tend to approach each other. Astronomers believe that this force can be channeled along the unseen threads of the cosmic web, which expands and plays a crucial role in shaping the universe.

A catastrophic event

Called IC 2431, the trio photographed by Hubble will one day become a single, enormous galaxy. All galaxies evolve within a cluster, and the smaller ones always end up being “swallowed up” by the larger ones. But in the case of a trio of galaxies, the three objects attract each other (while “pulling” each one on their side) like a huge ballet. But they eventually merge into a single element.

As in our galaxy, the Milky Way, which would have merged with Gaia-Enceladus 8-10 billion years ago, scars from the catastrophe will be visible. The merger will indeed cause major gravitational disturbances. This will generate large frictional forces between cosmic gases and dust. Very high-density clusters then form and collapse in on themselves, generally giving rise to a wave of star births.

Furthermore, the stars and dark matter of the galaxies involved during the merger are increasingly affected as the galaxies approach each other. At the end of the merger, the orbits of the stars have been completely modified. Along with dating and mapping stars, these changes in orbit are the “scars” that astronomers track to understand the evolution of a galaxy.

In the newly captured image of IC 2431, the three galaxies can be seen “devouring each other”, as well as a tumultuous mix of star formation and tidal distortions, caused by the gravitational interactions between the galactic trio. The center of the image is also obscured by a thick cloud of dust, although light from a background galaxy can penetrate its outer edges.

At the same time, after a merger, the supermassive black holes at the center of each galaxy approach each other and are locked in a binary or ternary orbit. These may also end up merging into a gigantic and unique supermassive black hole. Experts believe that gravitational wave signals from one of these colossal mergers have yet to be detected within IC 2431, possibly because they occur at a frequency beyond the range of our current detectors.

Observing such objects can help understand how massive galaxies grow and evolve over millions and billions of years, and how our universe will continue to evolve.

Leave a Comment