“If you are writing any book about the end of the world, what you are really writing about is what’s worth saving about it.” –Justin Cronin
Well, it’s Friday again, and that means it’s time to dip into the question/suggestion box, and see what you’ve come up with for me. This week’s Ask Ethan comes from our reader Michael Acosta, who wants to know about the end of the world. Not, mind you, the way the world is actually likely to end, but in a way that would be satisfying to an aspiring science fiction writer.
In this wonderful science fiction book I am writing, there is a subplot involving the demise of the Sun. How it is possible and how it can be possible within the span of a hundred years is a method I’ve yet come to and i am hoping you could point me in the right direction. The story takes place approximately 340 years in Earth’s history with the characters of Earth in that timeline aware of the Sun’s demise, and ultimately the Earth’s in about 50 years (of their future). I had read someplace about the possibility of a brown dwarf or red dwarf colliding with the Sun and I was leaning towards that direction, however, any input you can give me would be tremendously helpful…
Assuming we’re still constrained by physical reality, it’s pretty difficult to cause the Sun to die, or find a new way, astrophysically, to end all the life on our world in such a short time.
Still, let’s take a look at the options!
Someday, the Sun is going to die. Having run out of (hydrogen) nuclear fuel in its core, it’s going to expand — first into a subgiant, then into a red giant — and then it burns through the heavier elements that it can, finally expelling its outer layers in a planetary nebula.
But that’s too slow of a process, something that won’t happen for billions of years.
Even if you could somehow make that process begin immediately — that is, if the Sun ran out of burnable hydrogen in its core right this minute — this is simply too slow for the story you want to write.
When a star runs out of fuel in its core, it leaves the main sequence, or the big line from lower-right to upper-left, above. For our Sun, that means it’s going to expand, increase its brightness (moving up the Y-axis), cool (moving to the right), and start burning hydrogen in a shell outside of the core.
How long will it take that transition to happen? Unfortunately for your story, tens of millions of years. So that’s too long, even if we could connive to make the Sun run out of fuel. But there are other ways to quickly heat up the Sun.
This globular star cluster is old, and based on its age — and the (normally great) assumption that all the stars in it formed at the same time — none of the stars in this image should be blue in color. But every once in a while, especially in dense stellar environments, two of these stars will find each other, collide or coalesce, and merge.
The way this would happen for our Sun, since it’s not a binary star, would be if another star was found to be on a collision course with our Sun, and eventually collided (and merged) with it. Plenty of material would be thrown off the star, Earth’s orbit would likely be significantly changed (due to the new gravitational properties of the star system), and the star that resulted would be more massive, hotter, and far more luminous.
Remember that the vertical scale is a logarithmic scale of luminosity, and that increasing the mass of our star by as little as just a quarter (25%) would double its power output.
There would immediately be another consequence, too: ejecta from the merger would certainly make its way towards Earth.
Under normal circumstances, the Earth’s magnetic field would protect us — at least for a little while — from these ionized particles. But if we happen to be experiencing either geomagnetic reversal or a geomagnetic excursion (where the Earth’s magnetic field strength drops to just a few percent of its present value), this could be immediately catastrophic.
Rather than just spectacular aurorae and the disruption of electromagnetic devices, we’d literally be inundated with unprecedented amounts of potentially lethal radiation, all because the Earth’s magnetic field failed to protect us.
And if you look at our geological history, it wouldn’t be a surprise if this happened sometime soon. In layman’s terms: we’re due.
So that would be how I’d do it: have a massive enough object — one that moves towards our Sun relatively slowly, so it can be tracked over a long timeframe — eventually collide-and-merge with our Sun, resulting in any number of the following:
- changes to Earth’s orbit (which a large mass could do), changing the maximum and minimum temperatures dramatically,
- ejected, ionized matter colliding with the Earth, resulting in either sustained electromagnetic disasters if our magnetic field is still as-is, or possibly in lethal radiation doses if we get a “perfect storm” of a geomagnetic reversal/excursion in tandem with this, and
- eventually (although this may take quite a bit longer; it takes a long time for stellar changes to make their way to the surface) an increase in luminosity that renders the Earth uninhabitable, eventually boiling the oceans.
The last possibility may realistically take too long for the timescale of the story you had in mind; some of the interesting (but technical) physics is detailed here.
Because the lives and deaths of Sun-like stars is a typically slow, gradual process, the Earth will likely remain inhabited for one-to-two billion years in the absence of a catastrophe like this, as it will take that long for the Sun to gradually gain enough luminosity (as it burns through its fuel) to boil the oceans and roast the Earth. But a little “help” from one of the most common stars in our galaxy — the red dwarfs — could help speed that up.
Be warned that even though it may be trackable for hundreds of years, because of the way gravity works, by time the object you’re thinking of collides with the Sun, it will be moving at many hundreds of kilometers-per-second (about 0.2% the speed of light), or really, really fast. But hey, it’s your story, and the fiction of how you want the world to end is limited only by your imagination! I owe you nothing but kudos for wanting it to be based in science, too.
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