Here's what it will look like when the Andromeda Milky Way and galaxies meet in billions of years

What happens when two galaxies meet? The Milky Way and the Andromeda galaxy are on a collision course and will meet in about 4.5 billion years. Today, astronomers using Hubble have provided a visual overview of what this collision might look like.

When two galaxies collide, it is highly unlikely that stars collide with each other. There is a great distance between the stars, measured in light-years. Thus, even though galaxies are huge conglomerations of stars, when two galaxies meet, it is extremely rare for two stars to meet.

Instead, the gravitational interactions between all the stars will change their trajectories. This is what happens in NGC 6052.

When NGC 6052 was discovered for the first time in 1784 by William Herschel, he thought it was a single galaxy. It has been classified as an irregular galaxy because of its strange shape. But now we know different.

We now know that two different galaxies merge into one. Both galaxies are named NGC 6052A and NGC 6052B. The pair is in the final stages of their merger and once things have stabilized, it will be a stable galaxy, and we will be able to call it NGC 6052 again.

The main image was taken with the Wide Field Camera 3 (WFC3) on the NASA / ESA Hubble Space Telescope. But Hubble also imaged the galaxies in December 2015 with its Wide Field Planetary Camera 2 (WFPC2).

The fusion of galaxies can be a magnificent site, because the gravitational forces cause long waves of stars in fluid forms. The Mice galaxies, NGC 4676 A and B are fusing and are one of the most striking examples of fused galaxies.

NGC 3921 is another pair of galaxies that are in the final stages of their fusion. Their merger began about 700 million years ago. Tails and star curls are the warning signs of a merger. Sometimes, as in the case of NGC 3921, the merger can trigger an explosion of new star formation.

NGC 3921 is close enough to be studied, and in 1997 Hubble's WFPC2 experienced an explosion of activity at the heart of the merging galaxies.

When Andromeda meets milky

What will happen in 4.5 billion years when Andromeda and the Milky Way will meet?

First, it will take hundreds of millions of years to conclude the meeting, if not billions. It is therefore unlikely that any civilization that goes through a fusion of galaxies and survives can actually face it. And in 4.5 billion years, our own Sun will be a red giant and there will probably be no humans or anything alive on Earth. But, if there are future distant relatives somewhere, somewhere in the Milky Way, that's what they could live, according to NASA.

First phase: As the Milky Way and Andromeda come closer, Andromeda will become bigger and bigger in the sky. It will look like a strange sword of glowing light.

Phase two: As they get closer enough, the giant molecular clouds measuring tens or hundreds of light-years will compress. Millions of brilliant blue stars will come alive, illuminating the sky and creating new constellations.

Phase three: The stream of stars that makes up the Milky Way in our night sky will be disturbed and scrambled. Gas, dust and new stars will redo our night sky. Many new stars will be massive and will live shortly before exploding as supernovae. These explosions will shape the destiny of all life on all the worlds nearby.

Phase four: On his first visit, Andromeda will pass the Milky Way. But then, after about 100 million years, it will turn around and the two galaxies will merge again. This will compress the molecular clouds again, which will trigger a new series of robust star-births. And many of these new stars will once again supernovae, so this will be a new wave of massive explosions. After this second cycle of supernovae, their stellar winds will carry away much of the remaining gas and dust that form new stars.

Phase five: Both galaxies will install and form an elliptical galaxy. Any trace of the two spiral galaxies that formed the new elliptical galaxy will have disappeared. Chances are that humanity will be long gone, and future astronomers observing the new galaxy will have no idea that we were once here, observing the universe and seeking to understand it.

In the 1940s, a Swedish astronomer wondered what would happen if the galaxies met. His name was Erik Holmberg and he built an analog computer with 200 bulbs to simulate galactic encounters. Based on his work, he predicted that galaxies could indeed collide and that their mutual gravity would eventually slow them down and that they would merge into one.

Most of the time, he was ignored or his idea was rejected. The idea seemed exaggerated and his electric light bulb computer was a whimsical invention.

Eventually, the idea gained traction and better telescopes caught these galaxies in the act. Now we know better. We know that galaxy fusions play an important role in the formation of the universe, even though we do not yet know everything.

sources: