This is the second in a two-part series about the science of THE FORCE AWAKENS. In this article I focus entirely on Starkiller Base. Part 1 covers everything else.
It took me several viewings of THE FORCE AWAKENS, and some reading up on the internet, to figure out exactly what the hell is supposed to be going on with Starkiller Base. That’s because the operation and storytelling behind it doesn’t make a lot of sense.
The idea is that Starkiller Base is a planet that has been outfitted with some really boss technology that sucks either matter or energy (this is somewhat ambiguous) from a star, then stores it in the planet. Then it shoots this beam of energy into hyperspace where it goes off and wipes out entire solar systems nearly instantaneously. In the process, it can suck so much energy from its parent star, that it somehow extinguishes it (whether or not it eats the entire star is ambiguous). Apparently, the whole planet can then go into hyperspace to find a new star.
There’s a lot here, so let’s break this into parts.
HAVE PLANET-GUN, WILL TRAVEL
At first I was very confused, because they never say in the film that Starkiller Base can move between stars like the Death Star could. So why build this insane monstrosity, if you can only use it once or twice before the star it is orbiting gets snuffed out? I mean, how often are you going to want to destroy *every* planet in another solar system?
But then Pablo Hidalgo of the Lucasfilm story group confirmed on Twitter that indeed it can go into hyperspace and hop between stars. This, to me, is even worse than if it were stationary. Now you have to destroy two whole solar systems every time you just want to destroy just one planet! First you eat a star, then you shoot the energy somewhere else. Why not just eat the star of the solar system you want to destroy and be done with it? I know what you’re going to say — well maybe that system is well defended. Ok fine, but the hyperspace travel time in THE FORCE AWAKENS seems to be drastically shortened, so that it only takes seconds to get from one planet to any other. You could get a defense force anywhere in the galaxy on short notice.
Second, it is insane enough to send the Death Star through hyperspace, but a planet!?! That just crazy crazy crazy. Let’s do some math. Again, we know Starkiller Base is about the mass of the Earth, since it has Earthlike gravity. We don’t know the mass of the Death Star, but they say it is the size of “a small moon.” Let’s consult this list of solar system objects ordered by size. Puck, one of the moons of Uranus, is perfect — it is 160 km in diameter, which is claimed to be the size of DS2. The Earth is 2 million times as massive as Puck. But that’s still only a lower limit to the mass of the Death Star 2. It isn’t solid — it is mostly empty space, with just floors, roofs, and girders. But for the purposes of this argument, let’s just say Starkiller Base is 2 million times as massive as the Death Star 2. It doesn’t matter if we are wrong by a factor of a few or even ten.
The energy it takes to move a planet is staggering. And it gets worse the faster you go. As you approach the speed of light, your mass actually increases. To reach 99% of the speed of light, your mass gets larger by a factor of 7! And it goes up exponentially from there. The more mass you have, the more energy it takes to accelerate you, so to go the speed of light it would take infinite energy.
Fortunately, there is a loophole around this in the Star Wars universe — you never have to go faster than the speed of light. You just go into hyperspace, where distances are shorter. It isn’t totally clear how this works though. Presumably you have to have some kind of acceleration through regular space to get into hyperspace, or else this is just teleporting. And besides they show ships sort of zooming through regular space before they rip into hyperspace, and then they decelerate out the other side.
So, for fun, let’s figure out how fast we could get a planet going if we could capture the energy of the sun for an entire day. The power output of the sun is 4 * 1026 Watts. Watts are Joules per second. So in a whole day of 86,400 seconds, the sun puts out an energy of E = 3 * 1031 Joules.
To see what speed that would give us, let’s keep it simple, and not worry about acceleration, and let’s use non-relativistic formula for kinetic energy. That is E=1/2 * m * v2, where m is mass and v is velocity. Setting the energies equal, and solving for mass, we get v=SQRT(2E/m). Plugging in the numbers, we get a velocity of 6000 meters per second. That may seem like a lot, but it is only 0.00002 times the speed of light. (Note that this is slow enough that my use of the non relativistic formula was ok).
In short, capturing the energy of a star for even a whole day can’t move a planet very fast. Because it is insane to try to move a planet! But my beef isn’t so much with the numbers. Maybe Starkiller base can get all the energy of a star. Maybe hyperspace doesn’t work like I think it works. Instead, my real problem is that once you can move planets through hyperspace, it makes the people in Star Wars effectively gods. If you can move whole planets, there need not be desert planets or ice planets anymore. Forget trying to rule by destruction, just run on a platform of moving all the planets into orbits so that they have weather like California. Or change the energy output of a star to whatever you want it to be.
General Hux should have been like, “You can choke someone from two steps away, Emo Ren? That’s nice, I can MOVE PLANETS AND EAT STARS.” At least in Episode IV there was some sense that the Imperials knew they were badasses. Vader being subservient the Grand Moff Tarkin actually made sense. Anyone who can build a planet destroying weapon is actually far more fearsome that someone who can choke people a little easier and get a vague feeling about things.
This is a problem JJ Abrams makes over and over again in his movies — he doesn’t think through the consequences of his writing. He mortgages the future for a brief hit of surprise. In STAR TREK, now anyone ought to be able to make a red matter missile that can destroy a whole planet. The transwarp beaming that he invented means that people in Star Trek could beam themselves or weapons across the universe, obviating the need for starships. With Khan’s blood, you can bring people back from the dead. No more drama.
SUMMER IS COMING
Starkiller base steals energy or matter from its host star. This isn’t so insane on the face of it — some stars actually do steal mass from another star. Certain kinds of supernovae are stars that actually explode because they steal too much mass from a neighboring star. Here’s an artist’s conception.
Note that the stolen matter forms what’s called an accretion disk around the other star. That’s because of conservation of angular momentum as I mentioned in the previous article. It would have been cool to see a glowing hot accretion disk around Starkiller base — we’ve never seen anything like that in Star Wars before. See, just one of the ways you can make things even better the more science you know!
But in a binary star system, the matter is getting stolen because of the gravity of the secondary star. Planets don’t do this sort of thing no matter how close to the star they get, because they are too light. That’s ok — we know they can manipulate gravity in the STAR WARS universe. They have gravity on space ships, on the Death Star, and they can do ludicrous accelerations without getting splatterd into the back wall of their spaceship (remember, relativity tells us that gravity is equivalent to acceleration).
To sell this idea, they show Starkiller Base *right next to* the star it is stealing from. I can’t find any images online, but from the quick scene in the movie I’d estimate that the base is only a few stellar radii from the star. What would this do to such a planet? In fact, astronomers have detected hundreds of extrasolar planets in the last couple of decades, so we can actually compare this to real planets orbiting that close.
The fact that there are any massive planets orbiting really closely to their parent stars was a huge surprise. In our solar system, big planets like Jupiter form far out for a lot of reasons, not the least of which is because they there aren’t a lot of icy planitesimals out of which they form, close-in to a star, nor is there enough hydrogen to make them huge. But in 1995, when the first planet was found around a normal star other than the Sun, 51 Pegasi b, it was one of these “hot Jupiters” — a gas giant planet orbiting close to its parent star. Now we’ve found lots of these, so it has caused astronomers to revise some of their theories of solar system formation. There must be some process that causes some planets to migrate from far out where they are formed, down close to their parent stars.
While the Earth orbits the Sun at a distance of about 200 times the radius of the Sun, 51 Peg b is much closer to its star. It orbits at a distance of about 8 times the radius of its star. That means it is crazy hot — about 1800 degrees F, easily enough to melt lead! It is a gas giant, only about half the mass of Jupiter, but it probably has an even larger radius, because it is so hot it is puffed up.
And in fact, if we want to get something as close as Starkiller Base is to its star, we can look at the planet K2-22b. It orbits at only 3 times the radius of its star, but the star is much cooler than our Sun, since it is a red dwarf. Even still, the planet’s rocky surface is so hot it seems to be evaporating straight to space, producing a tail like a comet!
The bottom line is that when you get that close to a star, *any* kind of star, everything would melt — structures, metal, and of course people. And yet, on Starkiller Base there is snow! Friggin’ snow! I understand the metaphor here — the First Order is cold and lifeless, but come on! The metaphor has to link up to reality somehow.
I suppose you’d have to say that Starkiller Base’s was cold because it kept extinguishing stars, then traveling through hyperspace without a star. You might also say that it uses its shields to protect itself from the insane heat of the star it is stealing from. I guess there have to be shields, because troops on the base are lined up in formation, and there’s like a gigantic pillar of star-flame *right there* and they just kind of yawn and go on with boring speeches.
However, even the shields explanation doesn’t make much sense. Stars like the sun put out most of their light in the visible part of the spectrum. We can see through the shields, so they have to transmit visible light. And there is plenty enough visible light to kill you, even if the shields block the stuff we can’t see like UV and infrared. But from a storytelling perspective, involving shields is dumb too. You ought to be able to read what you see on screen and just get it right away (for all his faults, Lucas was a master of this). If you see a giant ball of fire, with piles of snow still on the ground, you should rightfully laugh at how silly that seems, and you shouldn’t need a fanboy to explain to you how that can happen.
There’s another problem with the star being that close. The star would take up a huge fraction of the sky on the planet. Let’s say the star is 3 stellar radii away from the surface of the planet. That’s easy geometry — the angle the planet would subtend on the sky is roughly the inverse tangent of 1/3. That’s a linear angle of 18 degrees. Our Sun is only half a degree in the sky. So the star above Starkiller Base ought to be 36 times the diameter of the sun in the sky, or 1300 times the area. Again, these numbers are just estimates, but we can confidently say that THE FORCE AWAKENS didn’t get it even close to right.
Having said all this, there is one cool thing about Starkiller Base being mobile. It lets me talk about rogue planets! There really are free-range planets wandering through the galaxy. We’ve seen them! There might be even more of them than there are stars. The idea is that after a solar system is formed, the planets often migrate from their initial positions, and a planet can be kicked out of the solar system. Simulations show this all the time. This new Planet Nine that has been theoretically predicted to be in our own solar system is one of these. That one (if it exists) is still bound to our star, but some are kicked out with such ferocity that they are doomed to wander the galaxy forever. Some may even have life, if the planet has enough core heat to sustain it. Wouldn’t that be crazy, growing up on a planet with eternal night?
DITCH? PLEASE.
In an attempt to give Starkiller Base an iconic look, they gave it a giant nozzle surrounded by a truly gargantuan ditch. The nozzle is clearly functional — it is used to both suck matter from the nearby star and shoot it out. I hope that reminded everyone else of this scene in SPACEBALLS. But the giant trench? It appears to have no function but to aggravate me.
Here’s the problem with that huge chunk taken out of the planet — the entire atmosphere of the planet would settle into it, leaving no more atmosphere on the surface. To see this, let’s calculate the volume of that giant ditch and compare it to the volume of a typical planet’s atmosphere.
The atmosphere of the Earth is a very thin layer. While the official edge of space is 100 km from the surface, 50% of the Earth’s atmosphere is within 5 km of the surface. That makes it easy to get a rough approximation of the volume of the Earth’s atmosphere. We take the volume of a sphere including Earth + half the atmosphere and subtract the volume of just the Earth. Then we’ll double the answer, since that was just counting half the atmosphere. The volume of a sphere is 4 * pi * R3 / 3. The radius of the Earth is 6371 km. Doing the math, we get that the Earth has 5 billion cubic kilometers of atmosphere. That may seem like a lot, but it means that the whole atmosphere of the Earth would fit in a cube 1700 km (about a thousand miles) on a side.
Don’t just take my word for it. Adam Nieman has created this stunning visual, showing all the atmosphere of the Earth as a pink sphere, compared to the size of the Earth. You can easily see that it would fit into the Starkiller Base trench.
But let’s do the calculation anyway. Since Starkiller Base is Earthlike, for the purposes of this calculation, I’m just going to assume it has the same dimensions as Earth. The circumference of Earth is roughly 40,000 km. Conservatively, I’ll estimate the depth of the giant trough as 10% of the radius of the planet, or about 600 km. In latitude, I’ll guess it spans 1/10 of the planet (4000 km), and in longitude, I’ll say it spans 1/4 (10,000 km) of the planet. Again these are rough numbers, and I’ll just say that makes a big box, rather than the spherical cross section that it would be. The volume of a box is length * width * height, so that’s 600 * 4000 * 10,000 = 24 billion cubic km! The 5 billion cubic km atmosphere of the Earth would fit in that giant Starkiller Base trough many times over.
But what about Venus? It is approximately Earth-sized (6052 km radius), and has a much thicker and denser atmosphere than Earth. At the surface, the pressure is 92 times the pressure on Earth! Since pressure is force per unit area, and Venus has about the same surface area as earth, this tells us that the atmosphere of Venus is exerting a force about 90 times greater than the Earth’s atmosphere is at sea level. Since force = mass * acceleration, and the acceleration due to gravity is about the same on Venus as it is on Earth, this tells us that the mass of Venus’ atmosphere is about 90 times that of Earth’s atmosphere.
But because gas is compressible, something 90 times the mass doesn’t take up 90 times the volume. Ninety percent of the atmosphere of Venus is within 28 km of the surface. On Earth, 90% of the atmosphere is within 10 km of the surface. Very roughly speaking, the volume of Venus’ atmosphere is about 3 times that of Earth. So it would still fall down that ditch hole.
That gives me a totally wacky idea. Maybe the First Order terraformed the planet out of which they built Starkiller Base. To do that, maybe they let built the giant ditch, and let the original atmosphere seep into it. Then they pumped in their own atmosphere to fill up the rest of the planet. Or even cooler, maybe the atmosphere was originally layered, with a dense gas on the bottom, and a breathable gas on top. They then cut the huge ditch in dimensions such that the dense gas fell into it, leaving the breathable gas to cover the planet.
In fact, Venus’ carbon dioxide atmosphere is a supercritical fluid at the surface. Supercritical fluids flow around like a gas, but dissolve things like a liquid. They can transfer heat efficiently, and this helps even out the day-night temperature on Venus. On Earth, supercritical carbon dioxide is used in both dry cleaning and decaffeinating coffee. Maybe on Starkiller Base something like it is used to regulate the laser.
Hey, terraforming ideas are almost always insane. In 1993 James Pollack and Carl Sagan considered ways to terraform Venus, as you can read in this pdf. They imagined hurling asteroids a the surface and having the explosions blow off the atmosphere. As they figured out though, there aren’t enough big asteroids to do it, it takes too much energy, and you quickly reach diminishing returns as the atmosphere thins. Instead, future visitors to Venus will probably just have to stay high up in the atmosphere. At 50 km up, the pressure is the same as on Earth, the temperatures are similar, and an oxygen dirigible would float above the carbon dioxide. You can read more about this idea for colonizing Venus here.
But now there’s a more serious point I want to make. Venus has an atmosphere that is more than 96% carbon dioxide. That’s a famous greenhouse gas that traps heat so efficiently that Venus has a surface temperature of nearly 900 degrees F. The Earth used to have a carbon dioxide atmosphere too, until life came on the scene and processed much of it into oxygen. So clearly life can change a planet’s atmosphere. But now we’re going back the other direction, and releasing carbon dioxide back into the sky. Check out this other visualization by Adam Nieman, below. The blue cube is the volume of natural carbon dioxide on Earth. The red is carbon dioxide humans have added to the atmosphere since the industrial revolution. We’re reverse terraforming the planet.
WHAT’S THE MATTER?
As I mentioned before, it is ambiguous whether energy or matter is being transferred from the star to Starkiller Base. To be more specific, they show that matter is being transferred, but that is insane. The only way this whole thing kind of works is if it is energy.
If matter is being drawn off the star and stored deep in the planet, there is a serious limit as to how much you can bring over. Stars are *huge* compared to planets. The sun is a million times the volume of the Earth. Here’s a comparison:
You can see the problem immediately — where do you put all that matter? Even if you sucked off a lot of it, planets aren’t hollow. Even if they were, you could only take a minuscule fraction of a star.
In the film, Starkiller base looks bigger than the relative Earth-Sun size, more like what we see in the above image with Saturn or Jupiter. But that’s not really physically plausible because very massive planets are gas giants and don’t have solid surfaces. So instead, let’s consider the smallest possible star we can, to make the relative sizes look closer to what we see on screen.
Let’s say it is among the smallest stars doing fusion, an M9 star with a radius of roughly 10% that of the sun. Then the star would only have 1000 times the volume of Earth. You still can’t fit much starstuff in Starkiller base. A small red dwarf star is about 10% of the mass of the sun — about 1029 kg. The earth is 6 * 1024 kg. So if Starkiller base ate only one ten-thousandth of its star, it would more than double the mass of the planetary base! This would more than double the gravity on the planet. Eat just one one-thousandth of the star and people would be pinned to the surface, blacked out. Each the whole star, and people would be crushed to a pulp, their bodies spread over the surface, just atoms thick.
And yet, that’s what they seem to imply in the movie! When the planet starts to implode, it looks like there is a star there underneath. This is just ridiculous. Writers, please resist the imbecilic urge to have a star be created out of nothing as a character’s legacy. First STAR TREK 2: THE WRATH OF KHAN, now this. I give up. I don’t care how metaphorically irresistible it is to have a star go out when a major character’s spark goes out of the universe — please have it make some goddamn sense.
Now it *is* actually possible for nature to put the mass of a star in the size of the Earth. That’s a white dwarf star. That’s what the core of our sun will become in a few billion years. However, there are a few problems with the First Order doing that. First, almost all of any star is hydrogen, and you can’t pack hydrogen into a white dwarf configuration. If you try to smash it together, it does fusion, and releases tons of energy. In fact, that’s what a star is! It is gravity smashing hydrogen together to make helium and energy. Instead a white dwarf is just the spent ash of a star. Also, once stellar material is packed as tightly as a white dwarf, it takes a lot of energy to pull matter back off. Then there’s the fact that white dwarfs have that insane gravity, and they are more than 100,000 degrees. Even if they are good at manipulating gravity in the STAR WARS universe, nothing about this works.
I HAVE THE POWER
What if, instead, Starkiller base is just siphoning off energy (i.e. photons) from the other layers of the star, and leaving the matter intact? After all, it is energy they are ultimately after.
For this argument, we need to understand how photons get out of the sun. A photon gets emitted when hydrogen atoms fuse, but then it only travels about a millimeter before it gets absorbed and reemitted in a random direction by another hydrogen atom. Then this photon does the same thing again. This “random walk” happens trillions of times before the photon makes its way out of the sun. This takes a loooong time. The sunshine we are receiving now was actually generated in the core of the sun about 200,000 years ago! It was created before modern humans existed, and has been working its way out of the sun ever since.
That means if we could magically absorb the photons from the outer layer of the sun, it would go dark. Then it would take photons thousands of years to work their way back to the surface. We keep the star intact — it is just a dark star for a while.
Stars don’t do exactly this in nature, but there is a class of stars that do disappear! Stars like R Coronae Borealis (called R Cor Bor stars) sometimes fade by a factor of more than 1000. In fact, R Cor Bor itself is a naked eye star, but for years it can just disappear from the sky. It is thought that carbon in these stars condenses into soot, blocking out the light of the star. But maybe it is an alien Starkiller Base!
In this energy-stealing reading of THE FORCE AWAKENS, when Starkiller Base implodes it is just the core of the planet we are seeing — it isn’t a new star. The star it is eating is still there, off-screen. Sounds perfect, right? The one problem is that they showed actual mass transfer (not just energy) from the star to the planet on screen. Energy travels in straight lines. Mass transfer happens in that little teardrop shape. To get around that, I’m going to say that their process pulls off a little mass, but it was mostly energy they are transferring.
Ok, to be really fair, this doesn’t make much sense either. How does the outer layer of the star stay up with the energy sucked out? How would you suck out just the energy? Also, even energy warps space. Still, sucking energy instead of matter just seems like it has more truthiness.
WRAP UP
Starkiller base is needlessly idiotic. It is the Jar Jar of THE FORCE AWAKENS — the movie would have been better without it. Story-wise, it didn’t need the planet destroying capability. We never see the world it destroys, nor have we met most of the pilots attacking it, so we’re never invested in that aspect of the story. Plus, we knew the good guys were going to win — we’ve seen it before (twice). The lightsaber fight in the snow, and the death preceding it, one the other hand, were gripping and emotionally stirring.
But even if Starkiller Base had to be in there, there were ways to make it work and not be so god-awful. Have it just drain the star of the system it was in as a form of terror. Had they done that, it would have solved almost all of the scientific problems THE FORCE AWAKENS had. Next time, consult a scientist!
Special thanks to Chelsea Harris and Ben Mazin for feedback on the first draft of this article. I’ve incorporated some of their ideas into this version.
