Fusion technology accidentally revolutionized astronomy

Pity the poor astronomer. Biologists can hold living examples on their hands. Geologists can fill sample cabinets with rock. Physicists even get to probe subatomic particles in laboratories built here on Earth. But throughout its millennial history, astronomy has always been a science of separation. No astronomer has ever stood on the shores of an alien exoplanet orbiting a distant star or seen an interstellar nebula up close. Other than a few captured light waves crossing the great void, astronomers have never had intimate access to the environments that stimulate their passion.

Until recently, that is. At the beginning of the 21st century, astrophysicists opened up a new and unexpected era for them: large-scale laboratory experimentation. High-powered machines, particularly some very large lasers, have provided ways to recreate the cosmos, allowing scientists like me to explore some of the most dramatic environments in the universe in contained and controlled environments. Researchers have learned how to explode mini-supernovae in their labs, reproduce environments around newborn stars, and even probe the hearts of massive, potentially habitable exoplanets.

How we got here is one of the great stories of science and synergy. The rise of this new large-scale, laboratory-based astrophysics was an unexpected side effect of a much larger, more fraught, and now quite in the news scientific journey: the search for nuclear fusion. As humanity has worked to capture the energy of the stars, we have also found a way to bring the stars to Earth.

Last month, with great fanfare, scientists at Lawrence Livermore National Laboratory Announced they had crossed a meltdown milestone. For the first time, more energy came out of a fusion experiment than was put in. Although the world is likely still decades away from any kind of working fusion power generator, the experiment was a scientific breakthrough that brought us one step closer to clean energy. and essentially unlimited energy through self-sustaining fusion reactions. To achieve this, the researchers relied on lasers to recreate a place where thermonuclear fusion reactions already occur: the core of the sun. They focused lasers on tiny pellets of hydrogen, mimicking the sun’s extraordinarily high temperatures and densities to compress hydrogen nuclei into helium and start fusion reactions.

Stars don’t give away their secrets easily. The lasers used are factory-sized requiring enormous power to do their job. It was in the process of building these multi-story light machines that scientists realized that, incidentally, they were also building an unprecedented tool for studying the heavens. Called High Energy Density Laboratory Astrophysics, or HEDLA, the field that has sprung up around these lasers has given astronomers entirely new ways to practice their craft.

Work began in earnest in the early 2000s with investigation of one of the most energetic events in the cosmos: supernovae, the titanic explosions that end the life of massive stars. Supernovae are powered by powerful shock waves that develop in a star’s core and then propagate outward, blasting the star’s outer layers into space. The heavy elements contained deep within a star are key to life eventually forming somewhere, so a longstanding question for astronomers has been whether a supernova explosion mixes up the core elements of a star. It crashes with the lighter ones on the surface, and through that mixture the essential elements are dispersed. -to-life heaviest elements in the entire cosmos. Working together, astronomers and plasma fusion physicists recreated the layers of a miniature star with thin strips of plastic and less dense foam-like material. Then they took out the ministar sandwiches with the big fusion lasers. Powerful shock waves were formed that tore through the targets and bent them like wet cardboard. It turned out that the mixture between the layers was real. The experiments confirmed an important part of the astronomers’ map of how elements cycle around the galaxy.

This was an exciting direction for astronomy. Astronomers now can’t just play with stellar material in a lab; they could do it over and over again. By adjusting one variable after another, they could perform actual ground-based experiments, test hypotheses, and see the results right before their eyes. They soon developed experimental platforms to study a wide range of astronomical environments, including the spinning disks of gas that accompany star formation and the collision of giant interstellar clouds. HEDLA still has limits; Not all astrophysical phenomena can be studied in the laboratory. Strong gravitational effects, for example, cannot be captured, because they would need the mass of a star, and no funding agency is paying for that. The trick for astrophysicists has been finding an overlap between the questions they want answered and the extreme conditions that giant fusion machines can create.

A sweet spot in the HEDLA Venn diagram lies in the search for distant worlds where extraterrestrial life could form. In recent decades, an “exoplanet revolution” has revealed that almost every star in the sky is home to its own family of worlds. Because life almost certainly needs a planet to emerge, understanding the different conditions on all of these alien worlds has become high on astronomers’ to-do lists. So far, many of the exoplanets we’ve discovered are strange beasts that look very different from the eight worlds that orbit our sun. Chief among these are the super-Earths, planets that weigh 2 to 10 times the mass of our world. We don’t have this type of planet in our solar system, and yet it happens to be the most common world in the universe. So what kind of planet is a super-Earth? Is this abundance of generic worlds worth investigating in search of extraterrestrial life?

The conditions on the surface of a planet, where life will form, depend to a large extent on what happens inside. Thousands of kilometers down, the pressures are so high that rocks are crushed until they ooze out like asphalt on a boiling day and iron liquefies. Under certain circumstances, the spinning motions of this molten soup drive planet-wide protective magnetic fields that support life. This is where HEDLA’s high-powered lasers come in: they prove to be a unique and perfect tool for probing the pressures deep inside planets. By using the lasers to squeeze rock and metal samples at these deep planetary pressures, researchers can see how the samples behave, discovering their resistance to flow (important for plate tectonics) or their ability to conduct electricity (important for plate tectonics). generation of magnetic fields).

This is also where I come in. The research my colleagues and I are conducting is part of a multi-year, multi-agency push funded by the National Science Foundation to make HEDLA a leading tool for understanding planetary conditions, including those of super-Earths. A recent experiment in this initiative, in fact, used the same massive 192-beam installation at California’s Lawrence Livermore National Laboratory where the recent fusion breakthrough occurred: the big daddy of all big lasers. The researchers wanted to understand how iron would respond to the pressures of the super-Earth, because swirling liquid iron in planetary cores is the key to creating planetary magnetic fields. Does iron remain liquid within a super-Earth, or does it “freeze” over time, solidifying into a crystalline lattice that would eliminate any possibility of a magnetic field? By driving iron at pressures 10 million times the pressure of Earth’s surface, the study tracked exactly when iron went from liquid to solid. From these data, the team discovered that super-Earths can keep their cores liquid long enough for magnetic fields to offer a billion years or more of planetary protection. If these results are confirmed, these large planets may have the right conditions not only to allow life to form, but also to evolve and thrive.

Experiments like this demonstrate just how far the new field of laboratory astrophysics has come in just a couple of decades. It is a story of convergence and even coming of age. Nearly a century ago, astrophysicists discovered the physics of thermonuclear reactions in stars. Their efforts were directed not to one day power the cities of humanity, but to answer an ancient cosmic question: What makes the stars shine? Only after the advent of Cold War nuclear weapons did some scientists begin to explore the possibilities of peaceful fusion energy. Now, in the process of moving a little closer to clean and abundant energy, we have reduced our own separation of star power and the cosmos as a whole. The universe is more in our hands than ever. And by capturing even a hint of its capabilities in our labs, we are reminded of how vast and magnificent it has always been.

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