The keys to harnessing fusion power—a clean, almost limitless supply of energy—sit in the heart of the sun. The only way we can access that heart is by listening to the sun’s heartbeat.
Last year the Department of Energy’s National Ignition Facility (NIF) made an astonishing breakthrough: the achievement of ignition in which the nuclear reaction at the core of the machine yielded more energy than when into it—a net positive gain. More recently, NIF made headlines again, this time by reaching ignition over and over again, demonstrating the group has mastered the techniques.
To start up a fusion reaction, NIF shines 192 laser beams simultaneously on a frozen pellet of deuterium (a stable isotope of hydrogen whose atoms contain not only one electron and one proton but also a neutron) and tritium (a radioactive form of hydrogen that has one proton and two neutrons). The lasers bring the temperature and pressure of the pellet up to such an incredible degree that those elements fuse into helium. That fusion reaction leaves a little bit of energy left over, which we can potentially use to power our homes, industry, and everything else that we depend on in our modern society. Best of all, the reaction leaves behind no nasty radioactive byproduct, and it’s much easier to control than traditional fission-based nuclear reactors. When you want the fusion to stop, you just pull the plug.
But as well-deserved as NIF’s achievements are, they’re a far cry from safe nuclear power running our civilization. While the reaction itself produced a net positive energy difference, that calculation doesn’t include the energy needed to power the lasers themselves. Another big problem is that we currently have no way of harvesting and storing that energy to produce electricity. If we want to make a massive leap in understanding nuclear fusion, there’s only one place to look: the sun.
The Sun Is a Role Model For How to Create Fusion Energy
The sun is a giant fusion factory. Deep in its core, hydrogen reaches temperatures of over 27 million degrees Fahrenheit and pressures so large it hardly makes sense to type the number. But I will anyway—it’s over a trillion psi (imagine the weight of 1,500 Empire State Buildings bearing down on every square inch, if you can). Those conditions slam the hydrogen nuclei together to form helium, at a furious pace. Every second, the sun consumes nearly 700 million tons of hydrogen and turns a small fraction of that into raw energy, enough to keep it shining for billions of years to come.
Fusion is a tricky game. Hydrogen atoms, which are usually made of just a positively-charged proton, really hate getting close to other atoms, and the extreme forces involved to make fusion happen are difficult to fully understand, especially when we’re trying to recreate those conditions safely on the surface of the Earth. But while we would just love to carve up the sun to take a peek on what’s going on in the core, we unfortunately do not the ability to do so (nor the inclination).
Thankfully, the sun itself has offered up a way to peek inside—no mega-engineering projects needed. The sun is a giant ball of plasma, made of superheated hydrogen and helium. Energy from the fusion eventually makes it way to the surface, carried by radiation and convective plumes of plasma. This roiling mass is just like any other ball of stuff in the universe: it’s vibrating.
The sun is constantly jiggling, sloshing, and wobbling, powered by the constant fusion reactions in the core, the release of energy from those reactions, and the struggle of that energy to make its way to the surface. In response, that surface is always in motion, much like the surface of the Earth is always in motion because of earthquakes and plate tectonic action happening all around the globe.
How We Model the Sun
Beginning in the 1960s astronomers started searching for signs of motion on the sun’s surface. Today, it’s an entire branch of astronomy, known as helioseismology, the seismology of the sun. To detect motion on the sun’s surface, astronomers rely on the light coming from that surface. When a patch of the sun happens to be swelling outwards, it will look like that patch is moving in our direction. That forward motion will add energy to the light coming from that patch, causing it to shift to the bluer, high-energy end of the electromagnetic spectrum. Conversely, when a patch is sinking, it will appear to be moving away from us, causing its light to shift to the red, lower-energy end of the spectrum.
These changes are very subtle, and not something you can pick out by eye. But astronomers have combined a globe-spanning network of powerful sun-observing telescopes with sophisticated computer analysis algorithms. They can make round-the-clock observations of the solar surface, to watch sunquakes vibrate across the face of the sun, see regions of the sun shudder from some hidden release of energy, and more.
These sunquakes are directly tied to the fusion happening in the core. And they’re the only way that astronomers can get a glimpse below the surface. To make this work, astronomers take different models of the solar interior, changing how the fusion process unfolds, how energy is transported from the innermost regions outwards, and so on. These different models will give different predictions for the size, strength, and frequency of sunquakes. Then astronomers match the observed sunquakes with the model that best predicts them. Rinse and repeat, with more detailed models and better observations.
Helioseismology has already proven its usefulness in verifying that our models of fusion reaction in the sun’s core are largely correct—despite other observations that had cast those models into doubt. Specifically, the fusion reactions produce a ghostly particle known as a neutrino, and we weren’t observing as many neutrinos as we thought we should. It turns out our understanding of neutrinos was to blame, not our understanding of the sun’s fusion process.
As we expand our capability to monitor and measure sunquakes, we can throw this data at ever more sophisticated models of the sun’s core. In turn, those models depend crucially on our understanding of nuclear physics, especially fusion processes operating at extreme temperatures and pressures.
Applying Our Solar Knowledge to Control Nuclear Reactions on Earth
And how do we apply a better understanding of fusion reaction? Through experiments like the NIF. As an example, our research on the Sun has proved that a tiny particle known as a neutrino is vital to understanding the fusion process, and this insight has guided the NIF design to maximize results. It’s all one big scientific circle of understanding: theoretical insights give us new ideas on how to control and exploit nuclear reactions; we test those ideas through observations of helioseismology; and we take those refined models and use them to develop better technologies of human-controlled fusion. With better technologies in hand, we can gain leverage from our insights for even better theoretical models, and the cycle starts anew.
We likely will not have fusion energy powering our homes in the next decade. It will take a monumental amount of work to figure out the nuts-and-bolts engineering to go from the net-positive fusion that we’ve achieved in advanced laboratories to a fusion power plant generating gigawatts of electricity. But if we’re going to get there, we’re going to need every tool available. If that means staring at the sun and examining its subtle vibrations, then so be it.
Paul M. Sutter is a science educator and a theoretical cosmologist at the Institute for Advanced Computational Science at Stony Brook University and the author of How to Die in Space: A Journey Through Dangerous Astrophysical Phenomena and Your Place in the Universe: Understanding Our Big, Messy Existence. Sutter is also the host of various science programs, and he’s on social media. Check out his Ask a Spaceman podcast and his YouTube page.
