Understanding conditions across the universe has not always been easy, especially after the discovery of extreme environments, but technological advances are allowing scientists to recreate those scenarios right here on Earth. In the last six weeks, three papers associated with the SLAC National Accelerator Laboratory in California have showcased the importance of experimental astrophysics.
One study, published in Nature Communications, looked at what happens in large gas planets like Jupiter. As it turns out, under huge pressure and heat, hydrogen turns into a metal.
“Understanding this process provides new details about planet formation and the evolution of the Solar System,” said Siegfried Glenzer, head of SLAC’s High Energy Density Science Division and the co-principal investigator of the study, in a statement. “Although the transition had already been predicted in the 1930s, we’ve never had a direct window into the atomic processes.”
The experiment was conducted at the Lawrence Livermore National Laboratory at the University of California, where scientists used a high-powered laser called Janus to compress and heat deuterium, a heavy form of hydrogen, to 250,000 times the pressure at sea level and 3,870 degrees Celsius (7,000 degrees Fahrenheit). This turned it into an ionized, metallic fluid, similar to that found in Jupiter.
Another team used the instruments available at SLAC to instantaneously heat up the surface of a graphite sample, and then used X-rays to observe how the sample changed. While we know that extreme heat and pressure occur during meteor impacts, scientists have now predicted that this could create a mineral called lonsdaleite – a carbon-based crystal that is stronger than diamond – when it hits graphite in the ground.
“We saw that lonsdaleite formed for certain graphite samples within a few billionths of a second and at a pressure of about 200 gigapascals – 2 million times the atmospheric pressure at sea level,” said Dominik Kraus, lead author of a paper also published in Nature Communications. “These results strongly support the idea that violent impacts can synthesize this form of diamond, and that traces of it in the ground could help identify meteor impact sites.”
Meteorite impacts could produce minerals harder than diamonds. solarseven/Shutterstock
Scientists are also looking at how to improve current experiments in order to push the limits of what can be tested in the lab.
The study of plasma is shared in astrophysics, fundamental physics, and engineering. The most extreme sources of astrophysical plasma are supermassive black holes, and one of the features astronomers are trying to understand is "magnetic reconnection" – a phenomenon where magnetic field lines are broken, releasing large quantities of energy associated with the sources of plasma.
“Magnetic reconnection has been observed in the lab before, for instance in experiments with two colliding plasmas that were created with high-power lasers,” said Frederico Fiúza, the principal investigator of the study published in Physical Review Letters. “However, none of these laser experiments have seen non-thermal particle acceleration – an acceleration not just related to the heating of the plasma. But our work demonstrates that with the right design, current experiments should be able to see it.”
Glenzer noted that the field of laboratory astrophysics is growing rapidly, with a number of technological breakthroughs allowing for research like this to be conducted.
“We now have high-power lasers to create extreme states of matter, cutting-edge X-ray sources to analyze these states at the atomic level, and high-performance supercomputers to run complex simulations that guide and help explain our experiments,” he said. “With its outstanding capabilities in these areas, SLAC is a particularly fertile ground for this type of research.”
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