Wed. Aug 10th, 2022

About 100 million light-years away, two galaxies give astronomers a sneak peek at the fate of the Milky Way.

So close that they are categorized under a single name, Arp 91, the spiral galaxies NGC 5953 and NGC 5954 are merging, with material from the latter extending towards and into the former. Details of this merger are visible in a new image from the Hubble Space Telescope.

Eventually, the two galaxies will merge to become a large elliptical galaxy according to our models of these colossal cosmic interactions. This is how we expect the Milky Way to end when it eventually merges with our own closest galactic neighbor, the spiral galaxy Andromeda.

arp 91 insertedArp 91. (ESA / Hubble & NASA, J. Dalcanton; Receipt: J. Schmidt)

In fact, galactic fusions are not uncommon in the universe. Space is large, and you might think that things would not encounter other things terribly often, but galaxies are not operating in a sea of ​​nothing. They are often associated with large filaments of intergalactic gas, which can act as material highways along which galaxies are drawn across the cavity.

We have discovered many such galactic collisions, but they occur on a time scale of about a billion years, so any collision in isolation does not reveal the entire process. Each one, however, is a snapshot of a moment in the process; by studying the collisions together, we can put together the course of events, as seen in the 2016 simulation below.

Arp 91 is at a stage where the two galaxies have not yet been significantly disturbed; their spiral structures are still largely intact. However, their interaction has triggered a burst of star formation in both galaxies, as inflowing gas generates shocks in clouds of molecular star-forming gas and pushes it into denser clumps that collapse beneath their own mass to form baby stars.

In addition, both galaxies have active galactic nuclei; that is, the supermassive black holes in their centers consume active material. This process generates powerful black hollow winds that push out into the surrounding gas, which – you guessed it – generates shocks that trigger star formation. So the two galaxies are actually very busy places.

Eventually, the two will merge, their spiral structures dissolving into a bright, almost functional galaxy, called an elliptical galaxy. However, it is at least a few hundred million years away. Whether humanity will be there to see it is an open question.

The merger between the Milky Way and Andromeda is even longer. Scientists predict that it will begin to occur about 4.5 billion years from now. However, we have very little to worry about; at that time, humanity will almost certainly be dead, gone, or unrecognizable.

But is not it nice to know what will happen to the place when we are gone?

You can download Hubble’s image of Arp 91 in full resolution or wallpaper versions from the ESA Hubble website.

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