Single-Particle Engine Reaches Temperatures Hotter Than the Sun — and Reveals Microscale Thermodynamic Surprises

Researchers have built an experimental heat engine from a single silica particle and driven it to effective temperatures rivaling those inside stars. The work, published in Physical Review Letters, is not intended to power devices but to probe how thermodynamics behaves at microscopic scales and how that behavior connects to certain biological processes.

The experiment was led by Molly Message, a Ph.D. student at King’s College London. Her team used a single silica bead 4.82 micrometers in diameter—about 5% of the width of a typical human hair—and levitated it at low pressure inside a Paul trap, a device that confines charged particles with an oscillating electric field. By varying the voltage applied to one of the trap’s electrodes, the researchers drove the particle into extremely high effective temperatures, recording peaks up to about 10 million kelvin. Those values are far hotter than the Sun’s surface and only a few million kelvin lower than common estimates for the solar core.

To put these numbers in context: much larger human-made facilities also produce intense heat. The planned International Thermonuclear Experimental Reactor (ITER) aims to sustain plasma near 150 million °C, while the Large Hadron Collider can create tiny, ultra-hot fireballs for fractions of a second. The new study shows that Sun-rivaling effective temperatures can also be produced at microscopic scales when fields and particle dynamics are precisely controlled.

Beyond the headline temperature, the experiment exposed several surprising thermodynamic effects that are unique to microscale systems. During some engine cycles the particle cooled when the surrounding conditions were made effectively hotter. The team attributes such counterintuitive behavior largely to the stochastic influence of thermal fluctuations, which exert an outsized effect on single particles and other small systems.

“Engines and the types of energy transfer that occur within them are a microcosm of the wider universe,” Message said. “Studying the steam engine brought about the field of thermodynamics, which in turn revealed some of the fundamental laws of physics. The continued study of engines into new regimes offers the potential to expand our understanding of the universe and the processes that drive its development.”

The published paper highlights several unintuitive behaviors at the microscale: engines can briefly run backwards, diffusion can become directed, and the local thermal environment can retain a memory of prior states. Those effects complicate efforts to model transport processes in cell biology and to design reliable micromachines.

Message and collaborators argue that a more detailed, experimentally grounded understanding of microscale thermodynamics could benefit both engineering and biology. For engineers, the insights could lead to improved microscopic engines and better control strategies for micromachines. For biologists, accurate models of microscopic energy exchange are critical for processes such as protein folding, which depend sensitively on thermal fluctuations and molecular-scale transport.

While the single-particle engine itself will not power household devices, it functions as a precise testbed for thermodynamic theory in regimes where randomness, small system size, and field-driven dynamics intersect. By tailoring electromagnetic confinement and drive, researchers can create extreme effective temperatures and use those conditions to observe how thermodynamic laws operate when macroscopic assumptions break down.

In summary, the experiment opens a pathway for studying and ultimately harnessing microscale thermodynamic phenomena, with potential implications ranging from nanoscale machine design to a deeper understanding of biological processes reliant on molecular energy exchange.