How To Destroy A Galaxy

We’re not sure if you’ve heard, but Rogue One: A Star Wars Story is out this week. It has an incredible cast and an unbelievably thrilling tale of derring-do, but the real stand-out star of the movie is, without a doubt, that infamous, moon-sized battle station.

Ever since those striking images of the Death Star appeared in the initial trailers, fans around the world could practically not stop salivating. As the ambitious director Orson Krennic notes to the looming figure of Darth Vader at one point, “the power we are dealing with here is immeasurable.”

Actually, for someone who was in charge of constructing the weapon of (super)massive destruction in the first place, saying it’s power is “immeasurable” doesn’t sound particularly scientific. So, because we are enormous geeks, we’ve decided to crunch the numbers for you. Warning: small spoilers may follow.

Destroying a City

^{Not quite planet-destroying yet. Star Wars via YouTube}

The Death Star in Rogue One is not yet complete. At the beginning of the movie, it has not yet been affixed with its planet-destroying power by the Oppenheimer-like figure of Galen Erso. At one point in the trailers, it appears to fire its superlaser down onto the surface of a planet, causing a lot of damage but not destroying it.

So how much energy would its superlaser need to carry to destroy, say, a city? Let’s take Washington D.C. as an example. Say the Death Star positioned itself directly above it and fired down to the surface right at the geographic center of the city. What would be sufficient to level everything from the White House to the Pentagon?

We’ll use the Tsar Bomba, the largest nuclear weapon ever detonated, as a benchmark. This weapon was the explosive equivalent of 50 Megatons of TNT. According to Nuclear Secrecy’s calculations, if detonated at the surface of Washington D.C., it would create a fireball just over 12 kilometers (7.5 miles) across, and would engulf an area of 113 square kilometers (44 square miles).

This would require 2.1 x 10¹⁷ joules of energy to be released by the superlaser, roughly that released in a 9.0M earthquake.

Destroying a Continent

Now let’s give the Death Star an upgrade, and target a continent.

During the formation of the Himalayas around 40 million years ago, the mass of a rather large continent was completely consumed by the mantle and destroyed. A recent study calculated this mass to be 450 quadrillion kilograms (about 500 trillion tons) of rock.

Let’s assume the continent is made of granite. At the surface, it’s about 15°C (59°F). We want to cause it to melt, which happens at 1,260°C (2,300°F). How much energy would the Death Star’s superlaser need to melt an entire continent? Fortunately, there’s an equation for this.

Multiplying the temperature change, the mass, and a value known as a material’s specific heat capacity together, scientists can calculate how much energy is required to make the temperature change take place. In this case, that would be 4.4 x 10²³ joules.

That’s not a very relatable number, so we can phrase it another way – this is roughly the same energy released in the dinosaur-killing asteroid impact that took place 66 million years ago.

Destroying an Ocean

^{Now we're talking. Harvepino/Shutterstock}

What if the Death Star wanted to root out an aquatic species by destroying an entire ocean? Well, fortunately, we can use the same equation to calculate the required superlaser energy too. Thanks, science!

The Pacific Ocean contains about 714 million cubic kilometers (171 million cubic miles) of seawater. At a density of 1,029 kilograms per cubic meter, that means that there's about 735 quintillion kilograms of seawater waiting to be evaporated.

The average surface temperature is about 17°C (62.6°F), and to get seawater to boil, we need to raise it to 102°C (215.6°F). Using the same equation as before, this means the Death Star would need to find 2.4 x 10²⁶ joules of energy to completely evaporate the Pacific Ocean.

That’s about 548 dinosaur-killing asteroid impacts. As it turns out, it takes a lot more energy to evaporate water than to melt a continent, so if the Death Star is coming your way, best go take a long dive underwater.

Destroying a Planet

Now we’re talking. The plans for the Death Star might have been stolen, but it’s now able to destroy an entire planet in a split second, as seen in A New Hope. In order to completely eradicate a terrestrial world, you would need the superlaser to overcome something called the “gravitational binding energy.”

This describes the minimum value a spherical, uniform object needs to keep together under the influence of gravity. If this value is exceeded by another energy source, it would tear the planet apart.

Planets are never uniform in terms of their composition, but let’s assume that they are for now. The Death Star decides that Trump isn’t worth the risk, and moves into position over Earth.

Using the mass of the planet, the gravitational constant, and its radius, we can use another lovely equation to calculate Earth’s gravitational binding energy. Turns out it’s 2.3 x 10³² joules, which is about 0.51 billion dinosaur-killing asteroid impacts.

That, dear readers, is how powerful the final Death Star was shortly before it was destroyed by the Rebel Alliance.

Destroying a Star

^{Scary times. Star Wars via YouTube}

Let’s just say that Luke Skywalker messed up, missed that vital thermal exhaust port with his proton torpedoes, and the Empire destroyed the Rebel base on Yavin IV. Oopsies. The Empire then proceeds to upgrade the Death Star even more so that it can unbind a main sequence star, like our own Sun.

According to a complex mathematical concept known as “virial theorem”, a star’s gravitational binding energy is twice that of its internal thermal energy, which can be worked out using yet another similar equation found here.

Our Sun’s binding energy, then, is about 2.3 x 10⁴⁰ joules, which is 52 quadrillion dinosaur-killing asteroid impact’s worth of energy. In order to unbind our local star – and destabilize and destroy the entire Solar System as a result – the Death Star’s superlaser would need to become 102 million times more powerful.

Destroying a Galaxy

Okay. Let’s say the Empire goes completely insane, finds nihilism attractive, and wants to take out the entire Star Wars galaxy. Let’s assume it has at least as many stars in it as the Milky Way, which is anywhere from 100 to 400 billion.

In order to take out, say, 250 billion stars – which we will assume are all like our Sun – then that would take 5.7 x 10⁵¹ joules.

One “standard” supernova releases around 1 x 10⁴⁴ joules, so if the Death Star took out the entire Milky Way, it would need to be powered by around 57.3 million supernovae. Ouch.

Good thing that Jyn Erso and co. managed to steal those Death Star plans, eh?

^{Someone's not happy. Star Wars via YouTube}