18 | NewScientist | 6 November 2010

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Dark matter may fuel galaxy’s glow

IS DARK matter leaving a calling card in the form of gamma rays at the centre of our galaxy?

Dan Hooper of the Fermi National Accelerator Laboratory in Batavia, Illinois, and Lisa Goodenough of New York University think so. They analysed two years’ of data from NASA’s Fermi space telescope and say the Milky Way’s centre emits more gamma rays than can be accounted for by known sources, such as pulsars. They suspect the annihilation of dark matter particles is to blame (arxiv.org/abs/1010.2752).

The gamma ray excess is at energies 10,000 times higher than the glut of gamma rays detected at our galactic centre in 2003 by Europe’s INTEGRAL probe. This makes it that much harder to explain with garden-variety objects, Hooper says. “Other than dark matter, we don’t know any mechanism to create this signal.”

However, Stefano Profumo of the University of California, Santa Cruz, disagrees: “We are far from the point where dark matter annihilation is the only explanation.” Charged particles hitting interstellar gas can also cause a gamma-ray glow, he says.

Cook then flake for really sharp spearsIF YOU want to make sharp stone spearheads, do what Stone Age cave dwellers did and cook them first. The trick allowed them to use a sharpening technique known as pressure flaking 50,000 years earlier than we thought.

The technique involves pushing a narrow tool against one side of a spearhead to release a thin flake of material from the other side. This allows for very fine control, producing sharp tips.

Paola Villa of the University of Colorado at Boulder and her colleagues looked for evidence

of pressure flaking on 75,000-year-old spearheads found in Blombos cave near Still bay in South Africa. They concluded that they could not have been pressure-flaked because the material, a cement-like substance called silcrete, would have come away in chunks, not flakes. And anyway, existing evidence of pressure-flaking went back only 20,000 years.

Then last year another team discovered that some of the artefacts had been heat-treated, which makes silcrete much easier to work with.

ROCKY planets a few times heavier than Earth that we thought might be life-friendly may lack one vital feature: a protective magnetic field.

Planets are thought to owe their magnetic fields to an iron core that is at least partly molten. But a simulation of super-Earths between a few times and 10 times Earth’s mass suggests that high pressures will keep the core solid, according to Guillaume Morard of the Institute of Mineralogy and Physics of Condensed Matter in Paris, France, and his team (arxiv.org/1010.5133).

Without a magnetic field, the

planets would be bathed in harmful radiation, and their atmospheres would be eroded away by particles streaming from their stars. So life would have trouble getting started on super-Earths, even if they lie in the habitable zone around their stars.

However, Vlada Stamankovic of the German Aerospace Center in Berlin reckons it is too soon to rule out molten iron cores – and magnetic fields – for super-Earths. Their interiors might get hot enough to melt iron, he says. “Actual temperatures could be much larger than assumed – we simply do not know.”

Super-Earths may be no place for life

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Villa returned to the spearheads and noticed that the scars where layers had come off were characteristic of heat-treated silcrete. This led her team to believe that the cave dwellers must have cooked their spearheads before flaking them.

To confirm their finding, the team made their own spearheads with local silcrete. They heat-treated some pieces and left others untouched. When flaked, only the cooked ones looked like the ones found in Blombos cave (Science, DOI: 10.1126/science.1195550).

Flamingos ready for their close-up

FEELING a little dull? Follow the lead of flamingos, which apply make-up to brighten their feathers. This touch-up allows the healthiest birds to continue looking their best, and so helps them signal their status as high-quality mates.

The bright pink colour of flamingos comes from pigments called carotenoids, which the birds acquire from their diet. Only healthy birds can gather enough carotenoids through their food to make bright feathers, but carotenoids fade quickly in sunlight, so feathers bleach over time.

To combat this, the flamingos turn to cosmetics. Juan Amat of the Doñana Biological Station in Seville, Spain, and colleagues found that greater flamingos, Phoenicopterus roseus, secrete the same carotenoid pigments via a gland near their tail.

When they preen, the flamingos spread the pigment over their feathers, brightening their colour. The team found this behaviour increased when the birds are choosing mates, and that brighter birds begin breeding earlier than drab ones (Behavioral Ecology and Sociobiology, DOI: 10.1007/s00265-010-106).

The effect doesn’t last, though. Once the birds have found a mate, they let themselves go. Preening activity tapers off after mating, and the birds’ plumage fades.

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