In most materials, heat tends to disperse. If the heat is not maintained on a pan, it will gradually dissipate as it heats its surroundings. But in exceptional states of matter, heat can behave like a wave, moving from one place to another similar to a sound wave that bounces from one end to another from a room. This undulatory heat is what physicists call “second sound”.
Now, a team of MIT scientists has first captured direct images of heat behaving like sound. The photograph was obtained within an exotic superfluous state of cold lithium-6 atoms through a new thermal mapping technique. The phenomenon shows the heat moving like a wave, bouncing as sound around its container.
Understand how the second sound moves could help scientists predict how it flows The heat within stars of ultra -dolted neutrons and high temperature superconductors, one of the “Graial Saints” of Physics whose development would allow an almost loss of energy transmission.
“It’s as if you had a water tank and put a half to boil – explains Richard Fletcher, co -author of the study Posted in Sciencein A statement -. If you will observe then, the water might seem completely calm, but suddenly the other side is hot, and then changes to the opposite side and so on, While water seems completely still, something that does not happen in normal circumstances. ”
But exotic materials called superfluous do not have to follow these rules. Created when fermions clouds (which include protons, neutrons and electrons) are cooled to Temperatures close to absolute zero, atoms within superfluids bind and travel without friction through the material.
As a result, heat flows differently through the material: instead of spreading through the movement of particles inside the fluid, as is usually the case, heat moves from one side to another inside superfluous as a sound wave. This second sound was predicted for the first time by The physicist was tisza in 1938, but heat mapping techniques, so far, have proven to be unable to observe it directly.
“The second sound is the distinctive seal of the superfluidity, but so far, in ultrafrios gases, it could only be seen in this dim reflection of the undensity undulations that accompany it -adds Martin Zwierlein, leader of the study -. The nature of the heat wave could not be demonstrated before”
To capture the second sound, the researchers had to solve a complex problem: to track the heat flow into ultra -African gases. These gases are so cold that they do not emit infrared radiation, on which the typical thermal mapping or thermography techniques depend.
Instead, the authors of the study They developed a method to track fermions couples through their resonance frequencies. Lithium-6 atoms resonate at different radio frequencies as their temperatures change, and the hottest atoms vibrate at higher frequencies.
When applying resonant radio frequencies corresponding to hotter atoms, scientists made these atoms vibrate in response, which allowed them to trace the flow of frames frame by frame. In a nutshell, very basic, words: it is As if they isolate a sound, atom per atom and pass it through a gelatin field, to see how it behaves.
“For the first time, we can photograph this substance as we cool it to the critical temperature of superfluousness and directly observe how it goes from being a normal fluid, where heat is balancing monotonously, to a superfluous where heat fluctuates from one place to another”, Concludes Zwierlein.