This week’s Hubble Space Telescope image shows two galaxies merging into one as the force of their gravity pulls them together. The two galaxies, NGC 5953 and NGC 5954, are so close to each other that they also have a common name, known as Arp 91.
Located 100 million light years away, this object shows the extreme conditions that can occur when two huge galaxies collide.
The two galaxies that make up Arp 91 are spiral galaxies, like our Milky Way galaxy, but the two appear to have different shapes in this image. It’s because of the angles we look at them from Earth. The lower galaxy, NGC 5953, is viewed from the front, while the upper right galaxy, NGC 5954, is viewed from a more oblique angle.
When galaxies merge in this way, the result can be either destructive or create a new type of galaxy. Sometimes one of the galaxies will be wiped out in the collision. Other times the two can merge to form a new, larger galaxy.
“Arp 91 provides a particularly striking example of galactic interaction,” write the scientists at Hubble. “NGC 5953 is clearly pulling on NGC 5954, which appears to extend a downward spiral arm. The immense gravitational pull of the two galaxies makes them interact. Such gravitational interactions are common and form an important part of galactic evolution. Most astronomers believe that collisions between spiral galaxies lead to the formation of another type of galaxies, called elliptical galaxies.
“These extremely energetic and massive collisions, however, occur on timescales that eclipse human life. They take place over hundreds of millions of years, so we shouldn’t expect Arp 91 to be any different in our lifetimes!