Hubble Captures Mesmerizing Detail of Two Galaxies on a Collision Course

Two galaxies, located around 100 million light years away, give astronomers a glimpse of the fate for the Milky Way.
They are so close they can be grouped under a single name, Arp 91. The spiral galaxies NGC 5953 & NGC 5954 are currently merging with material from the former extending towards the former. A new Hubble Space Telescope image shows details of the merger.

According to our models of the colossal cosmic interaction, these two galaxies will eventually join forces and become one giant elliptical star. This is how we predict the Milky Way will end up when it merges with Andromeda, our closest galactic neighbor.

Arp 91. (ESA/Hubble & NASA J. Dalcanton; Acknowledgement J. Schmidt

Galactic mergers are common in the Universe. Although space is vast and things might not bump into each other often, galaxies do not drift in a sealess ocean. These galaxies can be connected by huge filaments of intergalactic gases, which can act like matter highways that draw them together across the void.

Although we have seen many of these galactic collisions, they occur over a period of approximately a billion years. Therefore, any single collision won't be able to reveal the entire process. Each collision is only a snapshot of a moment in the process. However, by looking at the entire sequence of events (see the 2016 simulation) we can reconstruct the sequence.

Arp 91 has reached a stage in which the galaxies are not yet significantly disturbed; their spiral structures remain largely intact. Their interaction has caused a burst in star formation in both galaxies. Inflowing gas creates shocks in molecular star-forming gases, pushing it into denser clusters that then collapse under their own mass to make baby stars.

Both galaxies also have active galactic nuclei, which is to say that the supermassive black hole centers at their centers are actively consuming material. This creates black hole winds, which push into surrounding gas. As you can guess, this generates shocks that cause star formation. These galaxies are busy indeed.

The two will eventually merge, with their spiral structures becoming a bright, almost featureless type galaxy known as an elliptical. However, it is still a few hundred millions years away. It is not clear if humanity will still be alive to witness it.

Even further is the merger of the Milky Way with Andromeda. Scientists predict it will begin in 4.5 billion years. There is not much to be concerned about. However, by then, almost all of humanity will have died, disappeared or become unrecognizable.

Isn't it nice knowing what happens to the place once we leave?

Download Hubble's Arp 91 image in full resolution and wallpaper from the ESA Hubble site.