Discovery: Galaxies Might Cluster via the 'Cheerios Effect'

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bystander
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Discovery: Galaxies Might Cluster via the 'Cheerios Effect'

Post by bystander » Wed Dec 01, 2010 3:17 am

Galaxies Might Cluster via the 'Cheerios Effect'
Discovery Space News | Jennifer Ouellette | 30 Nov 2010
A new paper in the Dec. 1 issue of Astrophysical Journal Letters announces the discovery of a strange, boomerang-shaped galaxy nestled in a filament of hot gas connecting two massive galaxy clusters (Abell 1763 and Abell 1770).

Astronomers believe similarly shaped galaxies could serve as signposts to help identify other filaments, which in turn are an indicator of fertile regions for the formation of stars.

This unusual galaxy may offer some tantalizing clues about how galaxy clusters and superclusters form and evolve. Meanwhile, other physicists are looking a bit closer to home for clues about the deep structure of our universe -- namely, your morning bowl of cereal.

Clark University's Arshad Kudrolli and Michael Berhanu published a paper in Physical Review Letters this fall describing the so-called "Cheerios effect" and its implications for galaxy clusters.

Stars congregate in galaxies. Galaxies tend to bunch together in clusters, which in turn clump near other clusters to form so-called "superclusters", joined by long thin filaments of super-heated gas connecting the massive clusters. The result: huge, gravitationally linked walls of galaxies with vast empty spaces in between -- a gigantic cosmic web.
Heterogeneous Structure of Granular Aggregates with Capillary Interactions - M Berhanu, A Kudrolli Cereal And Saturday Morning Physics
Physics Buzz | 15 Sep 2010
A well-known effect in breakfast cereal helps scientists understand the universe.
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

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neufer
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Re: Discovery: Galaxies Might Cluster via the 'Cheerios Effe

Post by neufer » Wed Dec 01, 2010 4:40 am

http://en.wikipedia.org/wiki/Cheerio_effect wrote:
<<In fluid mechanics, the Cheerios effect is the tendency for small wettable floating objects to attract one another. An example of the Cheerios effect is the phenomenon whereby breakfast cereal tends to clump together or cling to the sides of a bowl of milk. It is named for the breakfast cereal Cheerios and is due to surface tension and buoyancy. The same effect governs the behavior of bubbles on the surface of soft drinks. This clumping behavior applies to any small macroscopic object that floats or clings to the surface of a liquid. This can include a multitude of things, including hair particles in shaving cream and fizzy beer bubbles. The effect is not noticeable for boats and other large floating objects because the force of surface tension is relatively small at that scale.

The quality of surface tension allows the surface of a liquid to act like a flexible membrane. A variety of weak forces act between liquid molecules to cause this effect. At the interface between water and air, water molecules at the surface are pulled forcefully by water molecules beneath them but experience only a weak outward pull from the air molecules above. Therefore, the surface of the water caves in slightly, forming a curve known as a meniscus.

Water adjacent to the side of a container curves either upward or downward, depending on whether the liquid is attracted to or repulsed by the material of the wall. For example, since water is attracted to glass, the water surface in a glass container will curve upwards near the container walls, as this shape increases the contact area between the water and the glass. A floating object which is less dense than water, seeking the highest point, will thus find its way to the edges of the container. A similar argument explains why bubbles on surfaces attract each other: a single bubble raises the water level locally, causing other bubbles in the area to be attracted to the first. Conversely, dense objects like paper clips can rest on liquid surfaces due to surface tension. These objects deform the liquid surface downward. Other dense objects, seeking to move downward but constrained to the surface by surface tension, will be attracted to the first. Objects denser than water will repel objects less dense than water: dense objects deform the water surface downward, and less dense objects tend to move upward, away from the dense object. Objects with an irregular meniscus also deform the water surface, forming "capillary multipoles". When such objects come close to each other, they first rotate in the plane of the water surface until they find an optimum relative orientation. Subsequently they are attracted to each other by surface tension.

Writing in the American Journal of Physics, Dominic Vella and L. Mahadevan of Harvard University discuss the cheerios effect and suggest that it may be useful in the study of self assembly of small structures. They calculate the force between two spheres of density ρs and radius R floating distance Image apart in liquid of density ρ as

Image

where γ is the surface tension, K1 is a modified Bessel function of the first kind, B = ρgR2 / γ is the Bond number, and

Image is a nondimensional factor in terms of the contact angle θ.

Here Image is a convenient meniscus length scale.>>
Art Neuendorffer

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