Fusion technology accidentally revolutionized astronomy

Pity the poor astronomer. Biologists can hold examples of life in their hands. Geologists can fill sample tanks with rocks. Even physicists can examine subatomic particles in laboratories built here on Earth. But throughout its millennia of history, astronomy has always been a class science. No astronomer has stood on the shores of an exoplanet orbiting a distant star or seen an interstellar nebula up close. Other than a few light waves traversing the great void, astronomers have never had such close access to the environments that stimulate their passion.

Until recently, that is. At the turn of the 21st century, astrophysicists have inaugurated a new and unexpected era for themselves: large-scale laboratory experiments. High-powered machines, particularly some very large lasers, have provided ways to recreate the universe, allowing scientists like myself to explore some of the cosmos’ most exciting environments in contained, controlled settings. Researchers have learned to explode tiny supernovae in their laboratories, reproduce environments around newborn stars, and even explore the cores of massive and potentially habitable exoplanets.

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

Last month, to great fanfare, scientists at Lawrence Livermore National Laboratory announced that they had moved past fusion. For the first time, more energy came out of the fusion experiment than was put into it. Although the world is still likely decades away from any kind of working fusion energy generator, the experiment was a scientific achievement, bringing us a step closer to cleanliness and essentially unlimited energy through autofusion reactions. To achieve this, the researchers relied on lasers to recreate a place where thermonuclear fusion reactions actually occur: the core of the sun. They focused the laser on tiny grains of hydrogen, simulating the sun’s unusually high temperatures and densities to compress hydrogen nuclei into helium and start fusion reactions.

Stars don’t give up their secrets easily. The lasers used are factory sized affairs that require massive force to do their job. In the process of building these light, multi-story machines, the scientists realized that they were also incidentally building an unprecedented instrument for studying the sky. Known as High Energy Density Laboratory Astrophysics, or HEDLA, the field that has emerged around these lasers has given astronomers entirely new ways to practice their craft.

The work began in earnest in the early 2000s investigating one of the most energetic events in the universe: supernovae, giant explosions that end the lives of massive stars. The supernova is propelled by powerful shock waves that develop in the star’s core and then propagate outward, blasting the star’s outer layers into space. The heavy elements in the depths of the star are the key to life that eventually forms somewhere, so one of the long-standing questions for astronomers was whether the supernova explosion mixed the basic elements of the star with the elements of its lighter surface, and through this mixing dispersed the elements the basic. -to-life is the heaviest element in the universe. Working together, astronomers and fusion and plasma physicists have recreated the star’s layers in miniature using thin strips of plastic and less dense foam-like materials. Then they dyed the little star sandwiches with large fusion lasers. Strong shockwaves formed that pierced the targets and shaped like wet cardboard. It turns out that the mixing of the classes was real. The experiments have confirmed a large part of astronomers’ map of how the elements orbit the galaxy.

This was an exciting direction for astronomy. Not only could astronomers now tinker with star stuff in the lab; They can do it over and over again. By adjusting one variable after another, they can perform real earth-bound experiments, test hypotheses and watch the results before their eyes. They soon developed experimental platforms to study a wide range of astronomical environments, including the swirling gaseous disks 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 it would require stellar mass, and no funding agency would pay for it. The trick for astrophysicists has been to find an overlap between the questions they want answered and the extreme conditions giant fusion machines can create.

A good point in the HEDLA Venn diagram is the search for distant worlds where alien life could form. In recent decades, the “exoplanet revolution” has revealed that nearly every star in the sky hosts its own worlds. Since life certainly needed a planet to emerge, understanding the different conditions of all these alien worlds has risen to the highest priority on astronomers’ to-do list. So far, many of the exoplanets we’ve discovered are strange beasts that look very different from the eight worlds orbiting our sun. Among them are Super EarthPlanets weighing from 2 to 10 times the mass of our world. We don’t have this type of planet in our solar system, yet it turns out that it’s the most common planet in the universe. So what kind of planet is a super-Earth? Is this generic bounty worth seeking out for alien life?

Conditions on the planet’s surface, where life will form, depend strongly on what happens in the depths of the planet. Thousands of miles away, the pressures are so high that rock is compressed until it exudes like asphalt on a scorching day and melts iron. Under certain conditions, the swirling motions of this molten soup drive protective planet-wide magnetic fields that support life. This is where HEDLA’s high-energy lasers come in: it turns out to be an ideal and unique tool for probing pressures deep in the inner planets. By using lasers to compress samples of rock and minerals to those deep planetary pressures, researchers can see how the samples behave, and discover their resistance to flow (important for plate tectonics) or their ability to conduct electricity (important for magnetic field generation).

This is where you come in too. The research my colleagues and I are conducting is part of a multi-year, multi-institutional campaign funded by the National Science Foundation to make HEDLA a key tool for understanding the conditions of planets, including those on super-Earths. In fact, one of the recent experiments in this initiative used the same massive laser-beam facility of 192 at California’s Lawrence Livermore National Laboratory where the latest fusion breakthrough — the big daddy of all large lasers — took place. The researchers wanted to understand how iron responds to Earth’s super pressures, because the circulation of liquid iron in planetary cores is key to making planetary magnetic fields. Does iron remain liquid inside a super-Earth, or does it “freeze” over time, turning into a crystalline lattice that kills any chances of a magnetic field? Pushing iron to a pressure 10 million times Earth’s surface pressure, the study tracked exactly when the iron dropped from a liquid to a solid state. From this data, the team found that super-Earths can maintain their liquid cores long enough for magnetic fields to provide a billion years or more of planetary protection. If these results hold true, these large planets may have the right conditions to not only allow life to form but also to develop and thrive.

Experiments like this one show just how far the new field of laboratory astrophysics has come in just two decades. It is a story of closeness and coming-of-age. Almost a century ago, astrophysicists explored the physics of thermonuclear reactions in stars. Their efforts were never meant to power human cities, but rather to answer an age-old cosmic question: What makes stars shine? Only after the advent of Cold War nuclear weapons did some scientists begin to explore the possibilities of peaceful fusion power. Now, in the process of getting a little closer to clean, abundant energy, we’ve narrowed our chapter on star power and the universe as a whole. The universe is in our hands more than ever. And in capturing even a fraction of his abilities in our laboratories, we are reminded of just how vast and everlastingly awesome they are.

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