Physicists at MIT Capture Images of 'Second Sound' for the First Time
A team of physicists at MIT have successfully captured direct images of the phenomenon known as 'second sound'.
Understanding 'Second Sound'
In certain materials, heat does not spread out from a localized source until it dissipates into its surroundings. This includes superfluids, which are states of matter that form when atoms are cooled to extremely low temperatures. In this state, the superfluid can flow infinitely without any energy loss or viscosity.
Physicists have predicted that in superfluids, heat propagates differently. Instead of spreading out, they theorized that heat would propagate as a wave, known as 'second sound'. This phenomenon can be described as the transfer of heat from one area to another in a friction-free state.
Assistant Professor Richard Fletcher explained that second sound can be visualized using the analogy of a tank of water: 'If you had a tank of water and made one half nearly boiling, the water itself might look totally calm, but suddenly the other side is hot, and then the other side is hot, and the heat goes back and forth, while the water looks totally still.'
Capturing Second Sound in Action
Capturing the movement of heat in superfluids is challenging because they do not emit infrared radiation. However, the team of physicists at MIT discovered that lithium-6 fermions resonate at different frequencies depending on their temperature. This allowed them to track the movement of resonating fermions and observe how heat was propagating as sound waves in the superfluids.
Professor of Physics Martin Zwierlein expressed excitement about their achievement: 'For the first time, we can take pictures of this substance as we cool it through the critical temperature of superfluidity and directly see how it transitions from being a normal fluid, where heat equilibrates boringly, to a superfluid where heat sloshes back and forth.'
The team plans to further study the behavior of heat in other ultracold gases and explore the applicability of their findings to other exotic materials, including the conditions inside neutron stars.
Implications and Publication
The team's groundbreaking achievement of capturing the phenomenon of second sound in direct images has been published in Science. This research opens up new possibilities for understanding and manipulating the behavior of heat in superfluids and other exotic materials.
By gaining insights into how heat propagates as sound waves in superfluids, scientists may uncover new ways to control and harness heat in various applications. Furthermore, this research could provide valuable insights into the conditions and processes occurring in neutron stars, which are incredibly dense and contain exotic matter.
