Movie: Spiral metamorphosis, merger of the Milky Way and Andromeda galaxies: the perspective from our Sun

The harsh reality of the distant universe with all of its violent interactions seems remote from our human existence and all might seem to be quiet and normal in our home the Milky Way. But it seems likely that in a mere 3 billion years, our neighbouring galaxy Andromeda and the Milky Way will fall together and have a close collision. They will likely merge and be reborn as a single giant elliptical galaxy over the course of another billion years or so. How might this metamorphosis play out and what might you see if you looked up at night over the next 4 billion years! The space between stars is so vast compared to their size that during a galaxy collision no individual stars actually collide with one another. So our sun and its family of planets will be taking a passive but exciting ride through the pair of coalescing galaxies and take on a spectacular view of the unfolding disaster in relative safety.

John Dubinski has set up a model system of colliding galaxies that reflects the current state of our the Milky Way and Andromeda system. There are still some uncertainties about the exact trajectories and masses of the two galaxies but I have set up a plausible case where they fall together and collide almost directly passing within 60000 light years of each other. Also, he only presents the view of the naked stars unobscured by the interstellar gas and dust clouds within the galaxy.

We get a chance to see it all from 4 perspectives: two fixed positions in space a million light years away and two sky views (this simulation), the first that projects the full 360 degrees of the sky onto an oval map and the second a view of one hemispheric dome of the night sky. In the sky views, one particle is identified as the sun within the model of the Milky Way and our view is always from this perpective with our attention directed towards the central bulge of the Galaxy making for a mind boggling spectacle.

In the sky views, the arch of the Milky Way is apparent at first as a band of stars and tiny Andromeda is seen scrolling past beneath the arch but slowly growing in size as it approaches. When the 2 galaxies intersect, the sun is flung out far from the colliding pair of galaxies and our view oscillates between a remote view of events to a wild ride right through the centre of the galactic bulge! The orbit of the sun is no longer circular but now follows a convoluted pattern with the distorted gravitational field of the merging galaxies. A final look back from the far flung sun shows the final merger of the two galaxies.

Credit: John Dubinski and John Kameel Farah

External view (from a fixed position in space a million light years away):
http://www.galaxydynamics.org/spiralmetamorphosis.html

Sky view (from the Sun):
http://www.galaxydynamics.org/futuresky.html