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.

The Quantum of Time

If I ask you for the smallest unit of time you can possibly think of, you might suggest a second, or a millisecond, or a nanosecond if you’re clever. But while these units are small enough to measure everyday events, physicists have to deal with cosmological forces and events on incredibly tiny scales, so they need to use appropriately tiny units to measure them. In 1899, German physicist Max Planck (who was also, incidentally, the founder of quantum theory) proposed a system of natural units of measurement called Planck units, stated in terms of five universal physical constants: the Gravitational constant, the Reduced Planck constant, the speed of light in a vacuum, the Coulomb constant, and Boltzmann’s constant. The system is based on the idea that space and time aren’t continuous—they’re quantised, which means that there’s a shortest possible measurable length (called Planck length) and a shortest possible measurable time (called, surprise, Planck time). Planck length is roughly 1.616 × 10^-35 metres, and Planck time is the amount of time it takes for a photon to travel a single Planck length, i.e. 5.391 × 10⁻⁴⁴ seconds. This is an unimaginably small quantity, but it helps to define the unimaginable small scale at which current physical theories break down—and helps physicists to study the beginning of the Universe, where the sequence of events in its early evolution was crammed into minute fractions of time.

The Eskimo Nebula

In 1787, pioneering astronomer William Herschel discovered the nebula NGC 2392, nicknamed the Eskimo Nebula because from the ground, it resembles a person’s head surrounded by a fur-lined hood. The nebula lies about 2,870 light years away in the constellation of Gemini, and just 10,000 years ago, its gases composed the outer layers of a star like our sun—but the dying star swelled to the size of Earth’s orbit and its outer layers flung into space in a final burst of glory, forming a planetary nebular. The star became a white dwarf, illuminating the gases around it. Herschel was actually the one who coined the term ‘planetary nebula’, using it to refer to round, ball-like nebulas that reminded him of Uranus, but it’s misleading because while their elements may one day be recycled back into planets, these stellar remnants otherwise don’t have much to do with planets—and yet, the term has stuck. The image above was taken by the Hubble Space Telescope in 2000, and shows far more of the nebula’s complex structure than Herschel could have ever seen: the bright central disc shows a bubble of material being blasted out by solar winds from the nebula’s core, so intense that they’re travelling over 1.5 million km/hr, and the outer disk contains a ring of strange orange filaments that stretch out like comets, yet are light years long. Astronomers are still puzzled about their origin, but suggest the filaments may have been formed by the collision of slow and fast moving gases.

(Image Credit: NASA/Andrew Fruchter)

Ginkgo Trees Stand Test of Time

“Living fossil” is an informal term used by biologists to describe species that lack living relatives.  While you might not personally think being called a fossil is a compliment, these organisms are actually quite impressive survivors.  The Ginkgo biloba tree, for example, is strange and unique amongst contemporary plants but incredibly similar to fossils dating back to the Permian, almost 270 million years! This means that even though every single other lineage of the Ginkgo’s relatives changed and adapted beyond recognition or died out, there are still Ginkgo trees growing today that would be indistinguishable from trees from hundreds of millions of years ago. If that fails to impress you, consider this: in Hiroshima, Japan there are still a handful of Ginkgo trees that survived the dropping of the atom bomb in 1945 living to the present day! If these hardy trees can withstand a disturbance of an A-bomb’s magnitude, it is no wonder they have managed to remain viable when so many other ancient plants could not.

Guest post written by Reggie Henke

Hox Genes

Hox genes are a type of “general purpose gene” that control the selection and placement of certain building elements in complicated organisms. For example, rat’s have a hox gene that controls whether a tail is “built” or not. In the rat’s case, this gene is turned on so there is a tail on the rat. While at first this may seem like useless information, once hox genes are put into an evolutionary perspective they become much more interesting. For example, chickens have a hox gene for teeth, but this gene is turned off. If this gene were to be turned on, and the beak gene were turned off, a chicken could theoretically have teeth. This is possible because the chicken’s DNA still contains the instructions for “building” teeth that its dinosaur ancestors once had. In this sense, hox genes can be helpful in explaining large leaps of evolutionary development, which before seemed impossible to occur so rapidly in such small amounts of time. But why does the hox gene exist? Hox genes are found because they control homologous to other organisms. In other words, many organisms of very different types and ancestries still have the same hox genes. Another example of hox genes in action is allometric growth. Allometric growth is a change in the rate of growth in a certain feature or dimension in comparison to the rest of the body. For example, some of the evolutionary changes responsible for bat wings are due to allometric growth. Since bat wings evolved out of ordinary paws, either the finger bones increased growth rate along with the skin connecting the bones, or the rate of body growth decreased while the paw rate remained constant. Both theories are examples of allometry.

(Sources: Berkeley/Nature)

Guest post written by slarsen88

Liquid marbles – drops that don’t splash

In 2001 two French scientists, Pascale Aussillous and David Quéré, discovered that coating a water drop with lycopodium powder gives it strange properties. The coated drop rolls and bounces over surfaces without losing any liquid. They called these weird drops “liquid marbles”. The particles in lycopodium powder are “hydrophobic”, meaning they are poorly wet by water. They sit so far out from the water, that they form a barrier between the water and the outside world. Liquid marbles are bizarre materials. They roll like glass beads due to their hard particle shells. Their shape changes as they bounce, however, due to their soft liquid cores. The presence of the particle shell lowers the temperature at which the liquid inside freezes. They do not have to be made from water and hydrophobic powder. At the Ian Wark Research Institute, Rossen Sedev and I investigated liquid marble formation from a range of aqueous and organic liquids. Our research showed how the particle wettability (the extent to which a liquid wets the particles) determines what happens when a liquid drop is mixed with powder. Our findings help people designing liquid marbles choose the best combination of powder and liquid. You can read more about liquid marbles at the Nature’s Raincoats website and in our publication in the journal Soft Matter.

Image Credits:

1. © Advanced Polymer Materials Lab. Osaka Institute of Technology, 2011

2.  © Nature’s Raincoats 2009.

3. Reprinted with permission from “Liquid marbles” by Pascale Aussillous and David Quéré in Nature, volume 411, page 924, 2001. Copyright 2001 Nature Publishing Group.

Guest article written by Catherine P. Whitby