Beautiful ‘flowers’ self-assemble in a beaker
With the hand of nature trained on a beaker of chemical fluid, the most delicate flower structures have been formed in a Harvard laboratory—and not at the scale of inches, but microns.
These minuscule sculptures, curved and delicate, don’t resemble the cubic or jagged forms normally associated with crystals, though that’s what they are. Rather, fields of carnations and marigolds seem to bloom from the surface of a submerged glass slide, assembling themselves a molecule at a time.
By simply manipulating chemical gradients in a beaker of fluid, Wim L. Noorduin, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS) and lead author of a paper appearing on the cover of the May 17 issue of Science, has found that he can control the growth behavior of these crystals to create precisely tailored structures.
“For at least 200 years, people have been intrigued by how complex shapes could have evolved in nature. This work helps to demonstrate what’s possible just through environmental, chemical changes,” says Noorduin.
The Glowing Spider-Worms of New Zealand
For over one hundred years, millions of tourists have flocked to the ancient limestone Waitomo Caves on New Zealand’s North Island, where a stunning species of fungus gnat called Arachnocampa luminosa live.
Unique to New Zealand and Australia, they are found in caves, grottoes, and other sheltered places. Arachnocampa means ‘spider-worm,’ as the gnat is known for the way their larvae hang strong vertical silk threads from their underground habitats. Since the larvae are luminescent, the thousands of tiny threads light up cave ceilings like a starry sky.
When a drop falls from a moderate height into a shallow pool, its impact creates a complicated pattern. The photo above is a composite image showing a top-down view 100 ms after such an impact. On the left side, the flow is visualized using dye whereas the right shows a schlieren photograph, in which contrast indicates variations in density. Both methods show the same general structure - an inner vortex ring generated at the edge of the impact crater and formed mostly of drop fluid and an outer vortex ring, consisting primarily of pool fluid, formed by the spreading wave. Both regions show signs of instability and breakdown. (Photo credit: A. Wilkens et al.)
‘Memory’ by artist Esther Paleologos
White dwarfs polluted with planetary debris
The Hubble Space Telescope has found chemical evidence for the building blocks for rocky planets in an extremely unusual place: the atmospheres of two burned-out stars. Called white dwarfs, these stars are small, dim shadows of stars that would have once been like our sun, and they reside 150 light-years from Earth in the young star cluster of Hyades. Hubble’s spectroscopic observations identified silicon and low levels of carbon, both of which are strong indicators of a rocky material similar to that which makes up Earth. “When these stars were born, they built planets,” said Jay Farihi, lead author of the study, “and there’s a good chance they currently retain some of them… Based on the silicon-to-carbon ratio in our study, we can actually say that this material is basically Earth-like.” The material is thought to have ended up in the atmosphere of these stars after they collapsed into white dwarfs, and the larger planets in their solar system nudged asteroids into star-grazing orbits. The stars’ gravitational pull tore the asteroids apart, and the pulverised debris fell into a ring around the white dwarfs and were eventually funnelled inwards to pollute the stars themselves. The discovery suggests that rocky planets may commonly assemble around stars, and may help us to understand what will happen to our solar system in five billion years, when our own sun burns out.