On my posts, we often think in terms of geologic time rather than time as it concerns an average human lifespan. Here, we’re more like rocks in our perception of time, or at least I am, thinking ahead billions of years. When trying to think in terms of ten trillion chess moves forward, there is one huge white elephant in the room as far as future events are concerned. That’s the cosmologically semi-imminent death of the Milky Way Galaxy.
That’s not as scary as it seems. A galaxy is really just an arrangement of stars that is subject to change. It doesn’t really matter so much to the individual stars of that galaxy. But we often intuitively think of our Milky Way galaxy as something that will permanently spiral its way through the universe unaffected by the lives and deaths of the individual suns that make up its fabric.
But this is not the case. The great familiar barred spiral that is our galaxy has only about four billion years to live. And it’s death will be as spectacular as things get, we’re set to ram headlong into the enormous Andromeda galaxy!
Andromeda Galaxy. A spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth, and the nearest major galaxy to the Milky Way. And there is almost certainly nothing we can do about it. No matter how advanced we get in the intervening years. And, if that’s not bad enough, the Andromeda Galaxy is much, much bigger than the Milky Way. Our galaxy contains about 300 billion stars. Andromeda contains a trillion or roughly twice the number estimated for the Milky Way. So the merger will be more like a swallowing up of the Milky Way by Andromeda rather than the other way around.
Moreover, M-31, as it is also known, is already so close that you can see it with the naked eye as a greenish-blue smudge in the constellation of Andromeda. That’s because it’s close, in terms of how vast the universe is, at just 2.5 million light-years away. But it’s getting closer. Fast. As in 68 miles per second fast. The collision speeds involved here are nearly unfathomable.
But don’t worry! Space is an unbelievably huge place. The distance between individual stars in galaxies are usually quite massive, barring solar systems with multiple stars already in them. So collisions between individual stars would be improbable during the event.
Think of it like this. If you shrink stars and space down to the size of golf balls for comparison, the average distance between stars even in the relatively dense galactic core would still be similar to two golf balls separated by about two miles or a bit over 3 kilometres. That leaves lots of room for stars to pass by each other without colliding. But they will affect each other through gravity.
What is Milkdromeda?
Within the gravitational chaos, some stars will be ejected from the merging galaxies entirely to wander the darkness of intergalactic space alone until they burn out. But the bulk the two galaxy’s stars will coalesce into a new galaxy. While no official name for the resulting galaxy has been adopted, the two current favourites are Milkdromeda and Milkomeda.
But Milkdromeda won’t be a beautiful new super spiral galaxy, that structure will be a thing of the past, but rather it will be a generally featureless and ho-hum elliptical or with some luck a disc type galaxy maybe with some remnant of spiral structure, a sad end for both universes.
Collision of Black Holes
But there is one exception to the highly unlikely collision rule. This one is highly likely. Each of the galaxies has at its core a supermassive black hole. In Milkdromeda, these two black holes will approach each other and eventually converge into a single, supermassive black hole. It’s unclear what this might do, though possibilities include the creation of a quasar or active galactic nucleus.
So you may be asking yourself what of the earth in this melee of impending galactic chaos? A model from 2006 doesn’t bode well. As the supermassive black holes coalesce, the sun could get caught up in the gravitational upheaval of it all and is predicted to have a 12 per cent chance of getting ejected, though that is subject to change, of course. But don’t worry, getting ejected would take millions of years and have little effect on the solar system. Plus, the increasing luminosity of the sun by that time will have long before boiled the oceans away, and the planet will be caught up in a runaway greenhouse effect so adverse that the surface may be completely molten awaiting the sun to eventually expand into a red giant and swallow it up.
Well … unless we’re still around and by that time are a galaxy-spanning Kardeshev type III civilization with the ability to save the earth and prevent the sun’s ejection with stellar engines and such. In that case, we will have just gained a trillion new stars to colonize in our great Milkdromedan Empire … well, unless someone else already has them. In which case, they will command the energy of over three times the amount of stars that we do. Not good!
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