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Tag: superfluid

  • Black Holes in a Blender

    Black Holes in a Blender

    Massive black holes drag and warp the spacetime around them in extreme ways. Observing these effects firsthand is practically impossible, so physicists look for laboratory-sized analogs that behave similarly. Fluids offer one such avenue, since fluid dynamics mimics gravity if the fluid viscosity is low enough. To chase that near-zero viscosity, experimentalists turned to superfluid helium, a version of liquid helium near absolute zero that flows with virtually no viscosity. At these temperatures, vorticity in the helium shows up as quantized vortices. Normally, these tiny individual vortices repel one another, but a spinning propeller — much like the blades of a blender — draws tens of thousands of these vortices together into a giant quantum vortex.

    Here superfluid helium whirls in a quantum vortex.
    Here superfluid helium whirls in a quantum vortex.

    With that much concentrated vorticity, the team saw interactions between waves and the vortex surface that directly mirrored those seen in black holes. In particular, they detail bound states and black-hole-like ringdown phenomena. Now that the apparatus is up and running, they hope to delve deeper into the mechanics of their faux-black holes. (Image credit: L. Solidoro; research credit: P. Švančara et al.; via Physics World)

  • Superfluid Heat Transfer

    Superfluid Heat Transfer

    Near absolute zero, as atoms slow down, some materials become a superfluid, a type of matter with zero viscosity. Superfluids do all kinds of strange things like generate fountains, leak from sealed containers, and form quantized vortices. Theorists also predicted that in a superfluid heat would slosh back and forth like a wave, even without any flow. They call this “second sound” and researchers have now detected it for the first time.

    In a typical experiment, we’d use an infrared camera to see how heat moves in a substance, but at the frigid temperatures of superfluids, that’s not possible. Instead, the team developed a method that measured the temperature of their atomic gas using radio frequency. When their lithium-6 fermions were at a higher temperature, they resonated with a higher radio frequency. Using radio frequency to probe the substance, they were able to observe exactly when heat stopped diffusing like in normal matter and switched to the superfluid second sound state. Since superfluids may live at the heart of neutron stars, further experiments will help us understand these exotic forms of matter. (Image credit: J. Olivares/MIT; research credit: Z. Yan et al.; via MIT News and Gizmodo)

  • Superfluid Instabilities

    Superfluid Instabilities

    Superfluids — like Bose-Einstein condensates — are bizarre compared to fluids from our everyday experience because they have no viscosity. Without viscosity, it’s no surprise that they behave in unusual ways. Here, researchers simulated superfluids moving past one another. In each of these images, the blue fluid is moving to the left, and the red fluid is moving to the right. In a typical fluid, such motion causes ocean-wave-like curls due to the Kelvin-Helmholtz instability.

    Instead, with a low relative velocity and high repulsion between atoms of the two layers, the superfluids form a tilted, finger-like interface (Image 1) that the authors refer to as a flutter-finger pattern. (Repulsion essentially sets the miscibility between the superfluids. With a high repulsion, the superfluids resist mixing.)

    With a higher relative velocity (Image 2), the wavelength of the ripples becomes comparable to the thickness of the interface, and the superfluids take on a very different, zipper-like pattern. Note how the tips detach and reconnect to the neighboring finger!

    With lower repulsion, the interface between the two liquids is thicker and breaks down quickly (Image 3). The authors call this a sealskin pattern. (Image credits: water – M. Blažević, simulations – H. Kokubo et al.; research credit: H. Kokubo et al.; via APS Physics)

  • Making Waves in Cold Atoms

    Making Waves in Cold Atoms

    If you take a glass of water and tap on the side of it, you’ll generate waves on the water’s surface. The form of the waves depends on surface tension and gravity, and viscosity governs how quickly the waves fade away. In a recent experiment, researchers performed an equivalent tap for a container of ultra-cold atoms, and the results they found were odd indeed.

    The researchers used lithium-6 atoms chilled so close to absolute zero that they could form a superfluid. The “glass” they were contained in consisted of intersecting laser beams, and the “tap” came from toggling the intensity of one of the lasers. This created rippling waves through the atoms that the group could observe.

    Measuring at various temperatures, the group found that the waves in the atoms always decayed the way one expects for a classical fluid like water. Even when the atoms transitioned into a superfluid, the wave decay did not change. Since superfluids are considered to have zero viscosity, you’d expect their waves to decay more slowly, but it turns out, that’s not the case! (Image credit: F. Mittermeier; research credit: M. Zwierlein et al., see also; via Physics; submitted by Kam-Yung Soh)

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    Fluids Round-Up

    Time for another fluids round-up! Here’s some of the best fluid dynamics from around the web:

    – Band Ok Go filmed their latest music video in microgravity, complete with floating, splattering fluids. Here they describe how they did it. Rhett Allain also provides a write-up on the physics.

    – Scientists are trying to measure the impact of airliners’ contrails on climate change. (pdf; via @KyungMSong)

    – Researchers observing the strange moving hills on Pluto suspect they may, in fact, be icebergs.

    – The best angle for skipping a rock is 20-degrees. Related: elastic spheres skip well even at higher angles. (via @JenLucPiquant)

    – Fluid dynamics and acoustics have some fascinating overlaps. Be sure to check out “The World Through Sound” series at Acoustics Today, written by Andrew “Pi” Pyzdek, who also writes one of my favorite science blogs.

    – Over at the Toast, Mallory Ortberg explores the poetry of the Beaufort wind scale.

    – Could dark matter be a superfluid? (via @JenLucPiquant)

    – Understanding the physics of the perfect pancake is helping doctors treat glaucoma. (submitted by Maria-Isabel)

    – Van Gogh’s “Starry Night” shows swirling skies, but just how turbulent are they? (submitted by @NathanMechEng)

    – The physics (and fluid dynamics!) of throwing a football – what’s the best angle for a maximum distance throw? (submitted by @rjallain)

    (Video credit: Ok Go)

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  • Fluid Dynamics and the Nobel Prize

    Fluid Dynamics and the Nobel Prize

    Last night marked the 2013 Ig Nobel Prize Award Ceremony, in which researchers are honored for work that “makes people LAUGH and then THINK”. Historically, the field of fluid dynamics has been well-represented at the Ig Nobels with some 13 winners across the fields of Physics, Chemistry, Mathematics, and–yes–Fluid Dynamics since the awards were introduced in 1991. This is in stark contrast to the awards’ more famous cousins, the Nobel Prizes.

    Since the introduction of the Nobel Prize in 1901, only two of the Physics prizes have been fluids-related: the 1970 prize for discoveries in magnetohydrodynamics and the 1996 prize for the discovery of superfluidity in helium-3. Lord Rayleigh (a physicist whose name shows up here a lot) won a Nobel Prize in 1904, but not for his work in fluid dynamics. Another well-known Nobel laureate, Werner Heisenberg, actually began his career in fluid dynamics but quickly left it behind after his doctoral dissertation: “On the stability and turbulence of fluid flow.”

    This is not to suggest that no fluid dynamicist has done work worthy of a Nobel Prize. Ludwig Prandtl, for example, revolutionized fluid dynamics with the concept of the boundary layer (pdf) in 1904 but never received the Nobel Prize for it, perhaps because the committee shied from giving the award for an achievement in classical physics. General consensus among fluid dynamicists is that anyone who can prove a solution for turbulence using the Navier-Stokes equation will likely receive a Nobel Prize in addition to a Millennium Prize. In the meantime, we carry on investigating fluids not for the chance at glory, but for the joy and beauty of the subject. (Image credits: Improbable Research and Wikipedia)

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    Superfluid Vortices

    Cooling helium to a few degrees Kelvin above absolute zero produces superfluid helium, a substance with some very bizarre behaviors caused by a lack of viscosity. Superfluids exhibit quantum mechanical properties on a macroscopic scale; for example, when rotated, a superfluid’s vorticity is quantized into distinct vortex lines, known as quantum vortices. These vortices can be visualized in a superfluid by introducing solid tracer particles, which congregate inside the vortex line, making it appear as a dotted line, as shown in the video above. When these vortex lines approach one another, they can break and reconnect into new vortices. These reconnections provoke helical Kelvin waves, a phenomenon that had not been directly observed until the present work by E. Fonda and colleagues. They are even able to show that the waves they observe match several proposed models for the behavior. (Video credit: E. Fonda et al.)

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    Superfluid Fountains

    Superfluids, a special type of fluid located below the lambda point near absolute zero, exhibit some mind-bending properties like zero viscosity and zero entropy. They are, in essence, a macroscopic manifestation of quantum mechanics. Here their thermomechanical, or fountain, effect is explained. This bizarre state of matter isn’t only found in laboratories, though. Scientists now think that superfluids may exist at the heart of neutron stars.

  • Neutron Superfluids in Stars?

    Neutron Superfluids in Stars?

    This image shows a composite X-ray (red, green, and blue) and optical (gold) view of the supernova remnant Cassiopeia A, located about 11,000 light years away. At the heart of this supernova remnant is a neutron star. After ten years of observations, astronomers have found a 4% decline in the temperature of this neutron star, which cannot be accounted for in current theory. Two research teams have independently found that this cooling could be due to the star converting the neutrons in its core into a superfluid. As the neutron superfluid is formed, neutrinos are emitted; this decreases the energy in the star and causes more rapid cooling. See Wired for more. #

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    Superfluid Helium Leaks from its Container

    Below a temperature of 2.17 Kelvin, helium becomes a superfluid, a state of matter boasting several unique properties including zero viscosity (resistance to flow). In this video, scientists demonstrate that property. When they pull the glass “bucket” of helium out at 2:50, the helium starts to leak out. The glass is solid but it contains numerous tiny spaces between its atoms. In its normal state, the viscosity of helium prevents it from escaping through those holes. But as a superfluid, its resistance to flowing goes to zero and it leaks right through the solid glass.