Job-hopping ants

Ants change careers as they age, transitioning from caretakers to cleaners and then foragers, according to a new study that tracked more than 1,000 ants for 41 days. “You can see a clear distinction between the three groups,” said Alessandro Crespi, a computer engineer at the Swiss Federal Institute of Technology and an author of the study, which appeared in the journal Science. Crespi and his colleagues used gridded heat maps to monitor carpenter ants in six colonies. “We put bar codes on the ants by hand and used a high-resolution infrared camera to take an image every two seconds,” he said. The ants were kept in the dark to simulate a natural setting. These images were converted into large data sets. When the researchers analysed the data, they discovered that young ants are primarily nurses. They stay close to the nest’s interior and ensure that ant larvae and pupae have sufficient food. Middle-age ants patrol the colony to verify that the colony is in working order and to make sure it is clean. “The ants are very clean, Crespi said. “There is a garbage pile in a specific place, and every dead ant and any kind of garbage is moved into this garbage pile.” The most dangerous job is foraging, since it requires leaving the nest and encountering the outside world, Crespi said. That’s a job for the oldest ants in the colony. Using their bar-coding technique and the cameras, the researchers hope to learn more about how the ants perform a multitude of tasks without the guidance of a leader.

Sindya N Bhanoo

Stellar duo discovered

Albert Einstein’s theory of gravity has passed its most stringent astrophysical test yet, correctly predicting how a closely orbiting pair of dense stars are spiralling towards each other. The findings rule out a subclass of competing theories of gravity, John Antoniadis of the Max Planck Institute for Radioastronomy in Bonn, Germany, and his colleagues report in Science. “This system provides a rare opportunity to constrain many non-Einstein models of gravity,” says Alan Kosteleck, a theoretical physicist at Indiana University in Bloomington, not involved in the study. The stellar duo comprises a neutron star — the ultra dense cinder of a supernova explosion and the compact remnant of a sun-like star, known as a ‘white dwarf’. Team member Ryan Lynch, of McGill University in Montreal, Canada, discovered the neutron star using the Robert C Byrd Green Bank Telescope in West Virginia. The star is classified as a ‘pulsar’ because as it rapidly spins, it emits radio waves that sweeps across the sky with clockwork regularity — about 25 times per second. Lynch and other collaborators then identified an aging white dwarf at the same location as the pulsar, and by observing it with the European Southern Observatory’s very large telescope in Paranal, Chile, they calculated the masses of both stars, which were crucial for testing the gravity theory. The pulsar, which tips the scales at twice the sun’s mass, is the most massive neutron star ever measured. General relativity predicts that celestial objects orbiting each other produce ripples in the fabric of space-time, known as gravitational waves. The effect is too small to have detectable consequence for objects that are not extremely massive and in tight orbits. But, because these two stars are so massive and separated by a relatively small distance (only twice as far as the moon is from the earth), they are expected to irradiate a substantial amount of energy as gravitational waves. Gravitational waves have yet to be detected directly. But the energy carried away by the waves would cause the orbit of two close stellar partners to shrink by a specific amount, according to general relativity. That effect, first documented in another pair of stars — a pulsar and a neutron star that are in a more widely separated orbit and less extreme in their heft garnered the 1993 Nobel Prize in Physics.

Ron Cowen
New York Times News Service

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