Ask Ethan #7: How to End the World

"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.

Image credit: the MODIS instrument on NASA's Terra satellite. Image credit: the MODIS instrument on NASA's Terra satellite.

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.

Image credit: NASA, ESA, K. Noll (STScI) / Hubble Heritage Team (STScI / AURA). Image credit: NASA, ESA, K. Noll (STScI) / Hubble Heritage Team (STScI / AURA).

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.

Image credit: Tom Harrison of New Mexico State, via Image credit: Tom Harrison of New Mexico State, via

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.

Image credit: STScI, NASA, Sepinsky et al, 2000; HST image of NGC 6397. Image credit: STScI, NASA, Sepinsky et al, 2000; HST image of NGC 6397.

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.

Image credit: Space Telescope Science Institute (STScI). Image credit: Space Telescope Science Institute (STScI).

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.

Image credit: Helmut Jerjen of ANU, via Image credit: Helmut Jerjen of ANU, via

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.

Image/illustration credit: Steele Hill / NASA. Image/illustration credit: Steele Hill / NASA.

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.

Image credit: Chu Research Group, CIRES, Colorado / Zhibin Yu. Image credit: Chu Research Group, CIRES, Colorado / Zhibin Yu.

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.

Image credit: United States Geological Survey / Wikimedia Commons user Intgr. Image credit: United States Geological Survey / Wikimedia Commons user Intgr.

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.

Image credit: Wikimedia Commons user Oliverbeatson. Image credit: Wikimedia Commons user Oliverbeatson.

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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I was wondering whether, if such a brown dwarf were careening towards our sun but not towards a direct collision that caused it to slingshot around the sun and spit out towards the Oort cloud, would the tidal forces of each star on the other have an effect that could cause a catastrophe on the earth that would work for his story?

By Michael R Haubrich (not verified) on 18 Oct 2013 #permalink

Thank you so much for answering my questions. This is a tremendous boost of information that I am happy you answered for me!!

By Michael Acosta (not verified) on 18 Oct 2013 #permalink

A couple of ideas: 1. A stellar sized black hole. When a star goes supernova, sometimes the explosion is not symmetrical. It gets a kick and goes speeding off through the galaxy. That could cause problems for the solar system. 2. A large clump of dark matter is headed our way. We detected it via gravitational lensing. We don't know if dark matter is able to form large clumps, but since we don't know, yours can.

Not sun-destroying, but how about an extreme version of the 1859 Carrington Event?

Or some small portion of the Oort cloud comets are exchanges from neighbouring stars & some of these are antimatter comets? One of which is journeying into the inner solar system on a sun-grazing orbit...

Which leads me to ask the questions ~
1] Would a distant antimatter star be indistinguishable from an ordinary star by all means of observation from Earth or would something subtle give it away such as light polarisation?
2] Would antimatter elements & chemistry be identical to ours?

By Michael Fisher (not verified) on 18 Oct 2013 #permalink

Definitely would go with non feeding black hole slipping into the solar system, casting Jupiter toward the sun which ejects earth from the solar system, personally like the pinball effect.

By Dead alien tech (not verified) on 18 Oct 2013 #permalink

Reading any such story, I would look for it to address the issues of how the disruptive object was or wasn't detected, and how the world's political leaders dealt with whatever advance knowledge they might have. Absence of those elements would be a glaring hole in the fabric of the story, even if they weren't relevant to the immediate plot as such.

Though, why specifically the sun? There are plenty of other astrophysical events that could be rapid slate-wipers, such as a gamma ray burster. Some of these have the added "bonus" for an end-of-humanity story, that they would also overcome whatever attempts we might have made at persistence via "off-site backup" such as colonies on Mars, in the outer solar system, or in another star system nearby.

@Michael Fisher #4: A distant antimatter star would be indistinguishable in isolation, because the electromagnetic interaction is symmetric under charge inversion (that is, + to - attract exactly the same way as - to +).

If you built an atom completely out of antiprotons, antineutrons and positrons, it would have exact the same energy levels and spectroscopy as its matter equivalent. That in turn implies that antimatter chemistry would be indistinguishable, since chemistry is driven entirely by electromagnetics.

The ATHENA, ATRAP and ALPHA experiments at CERN are working on testing this assumption precisely with antihydrogen.

Having said that, matter and antimatter are _not_ indistinguishable on the nuclear level. Specifically, the weak interaction (the force responsible, at low energies, for nuclear beta decay) maximally violates parity (left-right symmetry), and also violates the combination of charge inversion and parity (so called "CP symmetry).

The electrons which emerge from, for example, cobalt-60 decay, come out with left-handed spin. In a magnetic field, these electrons can be deflected preferentially in one direction rather than the other.

The beta decay of anti-cobalt-60 would produce right-handed spin positrons, which would deflect differently in an equivalent (upside down) magnetic field.

In principle, detailed observation of radioisotopes could possibly distinguish an isolated antistar. But unless that antistar were immersed in a large region of antimatter, we could identify it pretty quickly from the bow shock of gamma radiation as it (and its stellar wind of antiprotons) plowed through the normal-matter intersteller medium.

We can set limits on the antimatter content of the Solar System, based on observation. See, for example,, or search Google Scholar for "limits on cosmic antimatter".

By Michael Kelsey (not verified) on 18 Oct 2013 #permalink


Thanks you. That's a thorough answer ~ love it.

By Michael Fisher (not verified) on 19 Oct 2013 #permalink

Yo: Mike. My first advice is to know how the story will progress before you write it. My second is to ignore the advice about "end of sun" that we all give here. I think the story would work best if the cause of end of the sun is not spelled out clearly. Perhaps some hints: malevolent hypertechnological civilization is just playing a game? Novel unknown physical law is revealed? Good luck.

Djlactin makes a good point. It may be sufficient for the story to just start with the forecast as a fact, with whatever necessary mentions of scientific authority ("arguement from authority" is OK in fiction;-) may be needed to make it credible, e.g. a news headline to the effect that "'s update from NASA gives no sign of hope for averting (the event; whatever name you want to use for it)..."

Another scenario, with no relationship to existing science but potentially interesting for fiction: space telescopes observe an expanding area of roughly spherical shape, in which all the stars are just suddenly blinking out (or exploding), and NASA estimates 50 years (or whatever timeframe you like) until that area comes to encompass the Sun, and the Sun suffers the same outcome.

This implies "new physics" at work, or some kind of "contagious" effect that could touch on archetypal human fears on the part of the readers. It would also foreclose any option for humans seeking a new star system, as all the nearby candidates will also be destroyed by the expanding region of whatever-it-is.

If you want to imply "new physics" or "deliberate malevolent event," drop the "spherical region" and make it some other solid shape with linear edges and angles.

Alternately an "accident" by an advanced civilization, which also suggests the title "The Many Words for Sorry." In the conclusion of the story, as the end of the Sun approaches, SETI receives a signal and concludes that it is a string of apologies in all of the languages of intelligent civilizations in the galaxy. One portion of the message clearly renders into English as "We are sorry."


Though, all of this does bring up a bigger issue: if we knew that at some point in the future, some kind of solar event would render Earth life extinct, what would be our obligation to preserve the continuity of Earth life? That is, would it be acceptable to lapse into fatalism and resign ourselves to the end of Earth life (and who gets to make that decision for everyone)? Or would we be morally obligated in some way to seek to colonize a planet in a new star system in which Earth life could continue? What difference would it make if we had good reason to believe that some other civilizations had successfully migrated in the past?

I suspect that as the sun heats up, if it does it slowly enough, the oceans boiling are not going to trouble us. We're going to die of starvation long before then.

Plants fix carbon dioxide via the action of Ribulose-1,5-Bisphosphate Carboxylase (Rubisco, or RuBisCo), surely the most incompetent enzyme out there. With the help of an activation enzyme (Rubisco activase) it can fix only 3 to 10 molecules of carbon dioxide per molecule of Rubisco per second. In the absence of the activation enzyme the fixation rate tends towards zero. There are alternate paths of carbon fixation, but they are very minor compared to photosynthesis, and not at all an important source of carbon fixation in our food crops.

The problem is that the activation enzyme is heat sensitive. In most of our commercially important crops thermal inhibition of Rubisco activase occurs at surprisingly low temperatures. In wheat Rubisco activase inhibition starts at around 30 degrees Centigrade, and the enzyme denatures permanently somewhere around 40 degrees. As a comparison, Rubisco itself is heat stable to at least 45 degrees C.

So maybe some much lesser disaster, with a lesser increase in temperature, and consequent certainty of global starvation might give Michael Acosta some interesting possibilities to work with?

1) Death over the course of 100 years, or death with 100 years of warning? Somewhat different requirements.

2) As others have mentioned, a close encounter with a massive interstellar object would do the trick. Either brown dwarf of massive rogue planet would do, since it wouldn't have to stir the Sun to do us in; just screwing with the orbits of the planets could easily render Earth uninhabitable. Or, if you prefer, seriously stir up the sun. Wouldn't even have to make a permanent change to stir it enough to fry us.

By D. C. Sessions (not verified) on 20 Oct 2013 #permalink

If an exceptionally dense object (perhaps dark mater clumps or the remnants of the core of a neutron star) were to enter the solar system and be drawn into Jupiter's gravity, it could collide with the planet and join it's mass with that of Jupiter. The resulting object (a "Super-Jupiter"), could theorically have the needed mass to cause stellar ignition. Then, instead of the death of our sun, you would have a solar birth causing a binary star system. This does not actually answer the exact question asked, but it gives you a point from which to consider if this event would have similar effects on life on earth.


If you're interested in ways the world could end, check out:

There is an entire series starting a few weeks ago that has already discussed things like algal blooms, supervolcano's and asteroids. There will be upcoming posts on supernova's, solar flares, black holes and planetary collisions based on what I've seen in the Calendar of Destruction.

Scienceblogs is definitely a much better source of scientific information, the above site takes a humorous approach, but might still help give you other ideas or inspiration!

By Dr. Apocalypse (not verified) on 20 Oct 2013 #permalink

When I messed with SF writing, I wanted to know if it was possible to accelerate the rate of fusion in the sun to be able to harvest more energy from it, by manipulating the local gravity well or something.

A star passing through the solar system and merging with the sun was good enough for H.G. Wells, don't see why it wouldn't be good enough for anybody!

See: "The Star" by H.G. Wells. Don't read a plot summary or it'll spoil the twist! ;)

We might have a disaster beyond ourselves, but knowing the propensity of humans to war and invent ever more powerful weaponry, I would be surprised if our eventual demise wasn't of our own doing.

By Tony Rotz (not verified) on 21 Oct 2013 #permalink

I got one for you Ethan. If a spacecraft left Earth, and headed 'up', as in birds eye up; how far would it have to travel to be able to image the entire Solar System in one frame? I'm guessing a very long way.

By copernicus34 (not verified) on 21 Oct 2013 #permalink

Well, tell me what the field of view of the camera is, and how far out you consider the "Solar System" to be (do you want to include the Oort Cloud?) and the answer is just one trigonometric calculation away.

@CB, just choose a DOF that would include the planets, KB, and Oort, or if not feasible just a family pic of the planets.

By copernicus34 (not verified) on 21 Oct 2013 #permalink

If your FOV is 4pi steradian, then you can do that at an altitude of zero feet from the right location on earth.

If it's 2pi steradian, you can do it on occasions from the right location on earth.

If it's pi steradian, then you can do it from ~2500AU from earth if you move out of the ecliptic mean.

I seem to recall Phil Plait apperaing on a science show (maybe Morgan Freeman's series?), talking about how a big enough chunk of iron dropped into the core would essentially poison the fusion reaction, causing an early nova or supernova (depending on the star).

That would sound to me like a pretty fun sci-fi plot device. But you'd have to go reserach the details. How big a chunk do you need? Assuming the mass vaporizes near the corona and you don't use a MacGuffin to just place it in the core, how long does it take the iron to trickle into the center (if it ever does)? Would the splat cause a more immediate earth-death via effects not related to altering the sun's fusion? After the iron gets to the core, how long until the effects are seen on Earth? And so on.

I hope he was able to get Morgan Freeman to say "Holy Haleakala".

Why be complicated? Just have the Solar System enter a prviously unknown dust cloud that gets more and more dense as the story progresses. Have space probes sent to determine the size and density of the cloud, and folks will now exactly what the future will bring.

Last I heard, a black hole about the mass of the sun dropped into the sun would cause the sun to burn more stably for around twice as long. The matter can only fall in so fast. But the extra mass helps hold things together.

I would assume that a mass of iron would have little effect unless it were so massive that the heat needed to turn the iron into plasma caused a collapse as it got vapourised.

A one-solar-mass (Schwarzschild) black hole would be relatively tiny at ~3km in diameter, so that makes sense.

The purpose of the iron, I believe, is to displace hydrogen from the core, effectively reproducing what happens to much larger stars when they start producing iron naturally -- the iron itself costs energy to fuse, while the lighter, viable fusion fuel is pushed out of the core. The vastly lower density of the iron compared to the black hole is an advantage for our nefarious purposes.

Except I don't think that would really matter. If it's sub-critical (i.e. about 1/3 solar mass) addition of iron, the sun will probably last longer. There's no attempt to fuse iron and indeed doing so requires a supernova to allow the reaction to take place faster than the material can move away.

But the iron core isn't what causes the end of the star. A very rough guide is that the outer layers of hydrogen burn until there's not enough and it collapses. That causes the helium layer below (already fusing) to cause more fusion events and since (this is entirely off a now shaky memory) H-H goes as T^6 whilst He-He goes as T^8, when helium fuses, that puts a lot of extra energy into the system that makes the atmosphere shift. Some will compress the Carbon layer but it's easier to blow the hydrogen shell away, since it isn't being compressed into the deeper more dense layers but out into space.

And so on down to the Iron.

Where Iron would make a difference is that the mass of the atmosphere above has run out of enough material to continue to produce energy to keep it from collapsing to the Iron shell. The atmosphere therefore falls due to gravity and the Iron can't sustain fusion to cause another revival event and so the mass keeps falling in.

If it's massive enough, that can cause some further fusion but each step up has a lower multiplier but the temperature dependency goes up each time and iron is at the top there.


(technical term there :-))

But the presence of iron doesn't matter as long as there's enough H/D/T/He to keep the atmosphere stellar and stable. Only when there's not enough of that do you get the catastrophic death caused by iron.

But since the sun would have more mass suddenly, it will be able to keep the atmosphere it has for a bit longer before ejecting it in the red giant phase.

In effect, that's why the black hole doubles the life of the sun: it requires more than the He-He reaction to start the red giant phase for a two-solar-mass star.