Art Sunday: NGC 474 and the coming galactic set-to

NGC 474. Credit: P.-A. Duc (CEA, CFHT), Atlas 3D Collaboration. Image source: Astronomy Picture of the Day (APOD). All the individual points of light are stars within our own Milky Way galaxy and are in the extreme foreground. The two galaxies are 10,000 times further away than the stars. There are some other galaxies in the extreme background also; they are really far away and are marked by their elongated or fuzzy appearance. Click on the image for a high-resolution version. APOD is my home page and it should be yours too

Yes, this is art. Just so you know.

This beautiful image shows two galaxies: NGC 474 (the big one on the right) and the smaller anonymous one on the left. The two are probably interacting; that is, slowly being drawn together via mutual gravitational attraction. It’s a fight neither will win; within several hundred million years the two will comprise a single galaxy. NGC 474 itself is about 250,000 light years across, about 2.5 times wider than our own Milky Way. The whole thing is happening about 100 million light years away in the constellation of Pisces.

Galactic mergers are common. In fact, the Milky Way itself is currently swallowing several smaller galaxies (like this one), will soon be eating up a couple more (like these), and is set for a major-scale collision with another large spiral galaxy — Andromeda, or M31.

The two galaxies draw 170 miles closer to each other every second. That’s pretty fast, but they have a couple of millions of light years to cover, so don’t worry about the galactic set-to ruining this year’s World Series. In fact, we have several billion more Major League seasons to enjoy before the two galaxies collide and the lights go out.

No — We and our descendents won’t be around to see it. The Sun will get too hot for liquid water to exist in less than two billion years, so the lights will go out long before the collision makes everything higgeldy-piggeldy. It should be a good time nonetheless. The Sun and its attendant Solar System — now residing about two-thirds the way out from the center of the Milky Way, in the galactic suburbs — may be ejected into intergalactic space or fall in toward the core of the new merged galaxy. But it is unlikely that the dynamics of the planets themselves will be greatly affected. Stellar collisions, at least out where we live, will be very unlikely. Strange, no? Galaxies, like atoms and the Solar System, are mostly empty space.

Here is a beautiful simulation of the coming event shown from two points of view. Andromeda is the larger of the two and is initially at the top of the screen in both perspectives. Both are disc-shaped spiral galaxies; the Milky Way is shown face-on initially and Andromeda is shown at a slant. In the second perspective, the Milky Way is initially shown edge-on. The galaxies’ spiral structure is not built into the simulation at the beginning, but notice the way the interaction causes spiral arms to form. Notice too how many stars are flung out into space, never to return to their parent galaxy. Both sequences cover about a billion years’ time.

I think the whole thing is amazingly graceful and fun to imagine. What an amazing place we find ourselves living in.

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