The Star Wars films feature not one but three battle stations capable of destroying planets. In "A New Hope," the DS-1 Orbital Battle Station employs a superlaser powered by a hypermatter reactor to destroy Alderaan. Following the "Battle of Yavin," the Empire comes back with the Death Star II, an even more formidable weapons platform though it still employs the use of the hypermatter reactor powered superlaser.
In "The Force Awakens," the First Order, formed from the remnants of the Old Empire, have risen to create an even more formidable weapon: the Starkiller Base. The way this weapons platform operates is far different than its previous incarnations and, according to the film's novelization, uses an exotic form of energy: Dark Energy. So what exactly is this new "stuff" and what makes it different from the first two Death Stars. Come to think of it, how much energy does it take to destroy a planey anyway?
The Force that binds the Universe
While you are held together by the electromagnetic force - it is primarily the charge of electrons that make chemical bonds possible - on planetary and galactic scales it is gravity that permeates and holds everything together. Two particles attract each other through the gravitational force, something we can measure. All a lot of them together, like we see with planets, and all these particles will be bound together. The energy needed to keep all these particles together is the Gravitational Binding Energy.
The Gravitational Binding Energy is the minimum energy the Death Star needs to destroy a planet. If you toss a ball, it will eventually fall back to the surface but throw it hard and fast enough and it will leave the planet's surface forever. This speed is the escape velocity. Think of it as the energy needed for each and every particle to reach escape velocity, to be sent away and never return.
Both Death Stars possess the power of several "main-sequence" stars, the type that, like our own Sun, converts hydrogen into helium. Our Sun releases 300 yottajoules per second (that is 3 followed by 26 zeroes). Both Death Stars, each with the power of several Suns, will more than be able to decimate the Earth. Heck, with some effort it could blow Jupiter apart - it may take some time to build up the energy but it could do it. Now decimating Uranus is another matter as it is more massive and that mass is more packed than Uranus. This is something not even a couple of Death Stars working together could do. Which brings us to Starkiller Base.
Physics of Starkiller Base
It is obvious that Starkiller Base is a far more powerful weapon. Unlike the two previous Death Stars, this platform is able to wipe out entire solar systems with ease. When we first see the weapon in action, we see it literally sucking up a sun's plasma but is that even possible? Before I continue, I have to admit that Star Wars does not always get the physics right but as Rhett Allain points out in his Wired article and that is all right.
Several writers, including Allain, have looked at the possible physics behind Starkiller Base, and why not? Anything with that type of power is bound to be interesting. Geekwire science editor, Alan Boyle, looks at how this base uses plasma as a power source. We conclude that the First Order is pretty advanced when it comes to plasma physics.
If we use plasma for destructive purposes, how dangerous will it be? Kyle Hill of Nerdist answers this question in his article, "The Physics of Starkiller Base." Turns out it is very destructive. On its own, the new weapon could easily destroy five planets if it utilizes all the energy it takes to fuse all of the hydrogen into helium.
Storing all that plasma is a huge problem. Suns are massive and as Starkiller Base sucks up more and more of a sun's matter, the base's gravity increases to a point where everyone will be crushed to death. That is not all. As Starkiller Base absorbs a star, its spin increases so much that its rotation will fling everyone out into space. Either way, they are doomed but to be honest, the Empire was never known for workplace safety. Do we expect the First Order to be any different?
We can pretty much see that, despite Star Wars physics not being the most accurate (parsecs anyone?), plasma is not the likely source of the base's power. For a better understanding, we turn to the movie's novelization. Starkiller bases runs on a type of dark energy called "quintessence" which allows for a practically unlimited source of power, enough to decimate several planets over vast distances.
Starkiller Base uses an array of collectors on one side of the planet that gathers the dark energy in stages, and sending it to the planet's core where it is held in place by the planet's magnetic field. There is also an artificial containment field on the planet's crust to supplement the natural magnetic field. This made the base extremely vulnerable when fully charged as a collapse in the containment field would release the stored energy throughout the planetary core and create a new star.
A History of an Expanding Universe
In 1998, two research groups, the Supernova Cosmology Project and the High-Z Supernova Search Team, both discovered from examining supernovae that the Universe was not just expanding but doing so at an accelerated rate. Three members from the two groups were subsequently awarded the 2011 Nobel Prize in Physics: Saul Perlmutter, Brian Schmidt, and Adam Riess.
The notion of an expanding Universe led to the question of the Universe's ultimate fate. Would gravity eventually slow it down and cause it to collapse in on itself, or would it continue to expand forever? Perlmutter, Schmidt, and Riess' discovery answered that question: the Universe will expand forever and do so at an accelerating rate.
An Accelerated Expansion
No one knows exactly why the Universe is expanding at an accelerated rate but there are some hypotheses. One option is, there is no such thing as dark energy and our understanding of gravity may be incomplete and needs to be modified. The other option is there is some extra "stuff" throughout the Universe that pushes on the fabric of space-time.
Dark energy has a basis in quantum mechanics, which predicts that in the vacuum of space, particles are constantly winking in and out of existence and generating quantum vacuum energy. One of this proposed forms resurrects the "cosmological constant," an idea Einstein came up with to "hold gravity back" and achieve a static universe. The other is "quintessence" as seen in "The Force Awakens."
Both the Cosmological Constant and quintessence are scalar fields. Place a lot of thermometers throughout a room, you can map the temperature throughout the room at each point where there is a thermometer. Plot these values on a grid and you have a scalar field.
This brings up the two main differences between the Cosmological Constant and quintessence. While the Cosmological Constant is a constant scalar field, quintessence can vary over space and depending on its density, it can either be attractive or repulsive. It is believed that quintessence became repulsive about ten billion years ago.
Extracting Dark Energy to Destroy Planets
Whether the First Order can use Dark Energy to destroy planets depends on a few things. The first is whether dark energy interacts with matter. If it does not then it would be impossible. If it does then it depends on whether the scalar field is constant or varies.
The air is stagnant if an enclosed room's temperature is constant throughout the entire room. Air does not flow unless there is a thermal gradient or a difference in temperature across the room. The cosmological constant's hypothetical scalar field is constant across the entire Universe while quintessence's can vary.
If the scalar field interacts with matter, variations in the field means a force can be created to do work. This means that it is impossible to extract energy or do work with the cosmological constant but quintessence is far more exciting. Because it varies over space, the First Order can use it to create a force and store the energy it generates; energy that will be used to destroy entire star systems.
Is the Physics Right?
It appears that "The Force Awakens" makes several assumptions on Dark Energy; it interacts with matter, and the First Order can manipulate the field to do work. This answers some of the physics problems in the previously mentioned articles. What we see Star Killer Base sucking up is not plasma but rather the effects as it extracts energy from the Dark Energy field. It also means that the base's gravitational field does not have to increase so significantly that it will crush everyone and fling them out into space.
This does not mean there are not problems. Quintessence's scalar field is very small and only becomes significant over large distances - over cosmological scales. A base, like Star Killer Base, is too small to extract energy from the Dark Energy field and even if it could, the energy extracted might to too small to do anything. This by itself does not mean the movie is terrible. As Allain says about the physics in Star Wars:
It is not their job to have correct science in their movie. Sometimes, you have to bend the laws of nature (or ignore them completely) in order to tell a story—and that’s OK.
So while the movie has speculated and taken some liberties where physics is concerned, much of it is accurate, and they have managed to do so in a compelling and interesting manner.