VLT Reveals New Cosmic Interactions

ESA's Very Large Telescope surprised what seems to be a group of three large galaxies engaged into gravitational interactions with each other. The system lies 106 million light years away, in the direction of the Piscis Austrinus constellation, and is formed of NGC 7173, NGC 7174 and NGC 7176.

Two of the galaxies, respectively NGC 7173 and NGC 7176, are elliptical galaxies, while the other one is a spiral galaxy relatively similar in features to our own Milky Way. Elliptical galaxies hardly have any features, are composed of a population of low-mass old stars, which have lost the capability of triggering a new star formation process. Spiral galaxies are somehow younger than the elliptical galaxies, and consist of an accretion disk of matter, spinning around a central region. This central region contains a large density of stars and is called galactic nucleus. The accretion disk spreads out into space through arms resembling a whirlpool.

It looks like the galaxies NGC 7174 and NGC 7176 are currently interacting and exchanging matter, so that the spiral galaxy is provided with new material to trigger another star formation process. Studying the configuration of the system, ESA astronomers have concluded that the two elliptical galaxies have already interacted recently and the three will probably merge in the future, to create a massive spiral galaxy, tens of hundreds of times larger than our galaxy.

They are part of a galaxy cluster known as HCG 90, discovered in the 1980s, by Canadian astronomer Paul Hickson; it consists of four massive galaxies, three of which are represented by the galaxies enumerated in the upper paragraph, and another 12 smaller galaxies. The forth lies just about the three, outside of the image. NGC 7192 is a peculiar spiral galaxy.

A rather similar galactic cluster is represented by Robert's Quartet. Although galaxy clusters are very common in the universe, compact groups are generally small and formed of four to ten galaxies. Galaxy clusters, such as NCG 90, are extremely valuable for astronomical study, as they can be usually viewed during galactic interactions, that trigger star formation processes.