The image from the Hubble Space Telescope this week shows two galaxies that are merging into one as the force of their gravities pulls them together. The two galaxies, NGC 5953 and NGC 5954, are so close together that they have one shared name as well, known as Arp 91.
Located 100 million light-years away, this object shows the extreme conditions that can occur when two enormous galaxies collide with each other.
Both of the two galaxies composing Arp 91 are spiral galaxies, like our galaxy the Milky Way, but the two of them appear to be different shapes in this image. That is because of the angles at which we are viewing them from Earth. The lower galaxy, NGC 5953, is seen straight on, while the upper right galaxy, NGC 5954, is seen from a more edge-on angle.
When galaxies merge like this, the outcome can be either destructive or it can create a new type of galaxy. Sometimes, one of the galaxies will be annihilated in the collision. Other times, the two can merge together to form a new, larger galaxy.
“Arp 91 provides a particularly vivid example of galactic interaction,” the Hubble scientists write. “NGC 5953 is clearly tugging at NGC 5954, which looks like it is extending one spiral arm downward. The immense gravitational attraction of the two galaxies is causing them to interact. Such gravitational interactions are common and an important part of galactic evolution. Most astronomers think that collisions between spiral galaxies lead to the formation of another type of galaxy, known as elliptical galaxies.
“These extremely energetic and massive collisions, however, happen on timescales that dwarf a human lifetime. They take place over hundreds of millions of years, so we should not expect Arp 91 to look any different over the course of our lifetimes!”