18 | NewScientist | 5 November 2011

After a decade quietly circling its sun-like mate, an old star awakes, flaring for a few days before returning to slumber – until its next resurrection. In the end, however, this “recurrent nova” may explode fatally as a type 1A supernova, an insight that could help to explain dark energy.

Such supernovae are “standard candles” that show how fast the expansion of the universe is

accelerating. Knowing what kind of star produces them will allow better estimates of that acceleration. this in turn will shed light on dark energy, which is thought to drive the acceleration.

recurrent novae could be those stars: they have almost enough mass to collapse under their own weight and go supernova, and they grow by stealing gas from their mates. they also shed mass

Breathing new life into lung repair

tHere’S new hope for heavy smokers, people with asthma and those with chronic lung scarring: stem cells have been discovered that naturally rebuild alveoli, the tiny air sacs in lungs.

frank McKeon of the Genome Institute of Singapore and his team infected mice with flu. the virus quickly destroyed over half of the alveolate tissue – but within three months it had repaired itself.

the team found stem cells in the lungs had multiplied rapidly, creating hundreds of times their original number within a week. then they had migrated to sites of damage and formed pod-like structures before becoming new air sacs (Cell, DOI: 10.1016/j.cell.2011.10.001).

the team have isolated similar stem cells from human lung tissue. they are now searching for the chemicals that activate them, which could be harnessed to boost the lungs’ self-repair mechanism.

Pigment drives muscle movement in cats’ eyes

BRAIN not needed: the muscles controlling the slit-like pupil of a cat’s eye do not require nerve signals to drive their movement. A light-sensitive pigment in the iris can do the job instead.

Mammals were thought to rely on signalling between the eye and brain to resize the pupil and control the amount of light reaching the retina, but King-Wai Yau and his colleagues at Johns Hopkins University in Baltimore, Maryland, discovered that eyeballs isolated from animals that are active at night or at dusk and dawn – including cats, dogs and hamsters – continued to respond to light.

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Undead stars rise again as supernovae during outbursts, however, so it has not been clear whether they get massive enough to blow.

Bradley Schaefer of Louisiana State University in Baton rouge has used measurements of the recurrent nova CI Aquilae to show that during its eruption in 2000 it lost less mass than it had gained between eruptions. He concludes that it must gain mass overall, and so could become a supernova. the research will be published in The Astrophysical Journal.

They traced the effect to melanopsin, a light-sensitive pigment in the iris muscle. Eye tissue from mice lacking the gene for this pigment was unable to respond to light in the same way (Nature, DOI: 10.1038/nature10567).

The pigment is already known to play a similar role in birds, fish and amphibians. Stuart Peirson at the University of Oxford, who was not involved with the study, thinks it might provide dark-loving mammals with an additional pupil-shrinking tool that helps them avoid being dazzled if suddenly exposed to light.

The findings also hint at clinical uses of melanopsin in humans. Some forms of blindness result from the loss of light-sensitive rod and cone cells from the retina. Peirson says it might be possible to use melanopsin to make other cells in the retina light-sensitive instead.

SpIneLeSS they may be, but they are fearsome predators all the same. Hagfish – primitive vertebrates with a spinal cord but no backbone – have for the first time been seen hunting.

the snake-like animals are known to scavenge for food inside rotting carcasses, but via sea-floor video Vincent Zintzen of the Museum of new Zealand in Wellington and colleagues noticed a Neomyxine hagfish sticking its head into the burrows of red bandfish (Cepola haastii).

When it found an inhabited burrow it went inside, leaving its tail sticking out. Its body spasmed for a minute: Zintzen thinks this was a sign of the hagfish swallowing its prey (Scientific Reports, DOI: 10.1038/srep00131).

Hagfish hunt caught on camera

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