These galaxies are so close that the stellar formation that surrounds them both has its own name.
Arp 91 is a pair spiral galaxies located so close together (in relative terms space is large) that we can see their outer arms reaching towards each other and colliding. Intergalactic BFFs
Two galaxies that make up Arp 91 are here to greet you. Credit: ESA/Hubble & NASA. J. DalcantonA
These galaxies are like a happy marriage. They may share a name, but they are still their own individual entities. NGC 5953 is located in the middle of the frame. NGC 5954 is located just above and slightly to its right. Both are spiral galaxies but their shapes vary slightly due to perspective. The Earth is located more than 100,000,000 light-years from the sun, so Hubble cannot zoom in to capture them from a different angle.
The immense gravitational pull that each galaxie exerts on the other draws them together. Spiral galaxies were named and shaped by their unique swirling shape around a bright central, which is usually a supermassive dark hole.
This Hubble image's description notes that interacting galaxies such as Arp 91 represent only one stage in galactic evolution. Research suggests that spiral galaxies colliding eventually will merge into one elliptical galaxie, populated primarily with older stars, and lacking much of the gas and dust found in the hazy regions of Arp 91.
When it comes to understanding these interactions and determining their role in the constantly-evolving landscape of outer space, time and distance are two of the most important complicating factors. Each elliptical galaxie we have observed could have been multiple galaxies at once, just like Arp 91. It's all far away, and it happens so slowly (in relative terms), that the history of human-space study is only a small part of the larger picture.
