The Future of Our Galaxy

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Yesterday, NASA released a new image of what happens when galaxies collide. Earlier this year, the Chandra X-ray Observatory discovered something interesting: About 60 million light-years from our solar system, a massive cloud of extremely hot gas seems to give evidence that local gravity once brought a dwarf galaxy crashing into a bigger galaxy called NGC 1232. There are other hypotheses that might account for the presence of the cloud overlay: An abundance of supernovae and massive stars on one side of the galaxy could create this kind of cloud, which possibly represents a total mass as great as that of 3 million suns. But according to NASA’s press statement, the most likely explanation at this stage of analysis seems to be the big crash.
Galaxy collisions aren’t unheard of. You’ll find them all across the universe at large. Take a look at the “Mice Galaxies,” below:
The Mice have already passed through one another at least once, and now they’re getting ready for an ever-tightening embrace. While the universe is generally known to be expanding, there’s still enough gravity out there to frequently bring objects on the galactic scale into close interaction.
In fact, this phenomenon is actually about to hit close to home. According to a NASA simulation, this is what the night sky out your back window will look like in just 3.75 billion years:
That huge thing on the left, greedily sucking mass away from the disc of our own Milky Way, is the galaxy Andromeda – quite soon to be our new best friend, whether we like it or not. Right now, Andromeda is about 2.5 million light-years away. But in approximately 4 billion years, the two galaxies will begin to collide, and within 6 billion years, they will likely become forever joined by gravity and momentum.
So what happens in a galactic collision? Well, it’s not quite as bad as it sounds, but it’s not great either. Keep in mind that most of the volume of each galaxy is composed of the empty expanse between stars, so it’s not exactly like the collision of a meteor with the planet Earth, or of a football with a poorly shielded groin.
You should NOT expect that the stars and planets of the two galaxies will all smash directly into one another. Instead, we’re more likely to see the effects of the collision as a massive gravity disruption. As the galaxies pass through one another, the gravity of each will exert a pull on the mass of the other – which could mean that Andromeda and the Milky Way, much like the Mice, will end up spiraling into one another until they finally merge.
For a scientific simulation of this process, check out this absolutely mesmerizing video from the people at NASA and the Hubble Space Telescope site:
Now, the big question: Will this galactic merger/acquisition spell death for the human race?
The answer: Not necessarily, but with some important caveats. This article over at io9 has a pretty good write-up of the major considerations: relocation of our solar system relative to the rest of the galaxy; a black hole death orgy at the newly consolidated galactic center; surges in radiation from aforementioned death orgy; and finally the unrelated fact that by the time the galactic collision goes down, the escalation of our sun’s energy output will already have destroyed all possibility for life on Earth. In other words, if we’re still alive, we won’t be around to see what happens to our planet of origin.
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