28 Mart 2010 Pazar
Pulsars test relativity
" If both relativity and gravitational waves don't exist, our entire idea of how things came together in the cosmos will need a rethink "
We don't know why pulsars tick so regularly. The answer may lie in a paper presented in January to the American Astronomical Society meeting in Washington DC by John Singleton and Andrea Schmidt of the Los Alamos National Laboratory in New Mexico. They suggest the tick might be something akin to the sonic boom produced by supersonic aircraft as they accelerate past the speed of sound (arxiv.org/abs/0908.1349).
Relativity does not forbid the magnetic fields at the surface of a pulsar rotating faster than the speed of light, says Singleton. As they do so, his team suggests, particles of opposite charge are pushed to either side of the pulsar, where they emit radiation. The pattern of radiation is then sharpened by the superluminal boom of the magnetic field into a sharply defined pulse that is emitted into space. A similar effect shapes the sound waves emitted by an aircraft as it accelerates through the sound barrier. While the people inside hear a continuous rushing sound, the sound waves arrive at an observer on the ground as a single "boom" (arxiv.org/abs/0912.0350).
Singleton says his model can reproduce all the features of the radiation given out by a pulsar, replacing the hotchpotch of models needed before. That has got Jocelyn Bell Burnell, who discovered pulsars, interested. "They are explaining some features of pulsar emission that are difficult to explain, and very neatly," she says.
Other theorists are less impressed, but Singleton says that is to be expected. "If we're right - and I'm convinced we are - our model replaces 40 years of work that has employed hundreds of theorists. You would expect some hostility."
source : http://www.newscientist.com/
We don't know why pulsars tick so regularly. The answer may lie in a paper presented in January to the American Astronomical Society meeting in Washington DC by John Singleton and Andrea Schmidt of the Los Alamos National Laboratory in New Mexico. They suggest the tick might be something akin to the sonic boom produced by supersonic aircraft as they accelerate past the speed of sound (arxiv.org/abs/0908.1349).
Relativity does not forbid the magnetic fields at the surface of a pulsar rotating faster than the speed of light, says Singleton. As they do so, his team suggests, particles of opposite charge are pushed to either side of the pulsar, where they emit radiation. The pattern of radiation is then sharpened by the superluminal boom of the magnetic field into a sharply defined pulse that is emitted into space. A similar effect shapes the sound waves emitted by an aircraft as it accelerates through the sound barrier. While the people inside hear a continuous rushing sound, the sound waves arrive at an observer on the ground as a single "boom" (arxiv.org/abs/0912.0350).
Singleton says his model can reproduce all the features of the radiation given out by a pulsar, replacing the hotchpotch of models needed before. That has got Jocelyn Bell Burnell, who discovered pulsars, interested. "They are explaining some features of pulsar emission that are difficult to explain, and very neatly," she says.
Other theorists are less impressed, but Singleton says that is to be expected. "If we're right - and I'm convinced we are - our model replaces 40 years of work that has employed hundreds of theorists. You would expect some hostility."
source : http://www.newscientist.com/
Clearest sign yet of dark matter detected
Has proof of the existence of Dark Matter been found? And, more strangely, has it been found in a mine in the middle of Minnesota, instead of deep space? The answer to both questions may turn out to be yes...New Scientist reports that researchers involved in something called the Cryogenic Dark Matter Search may have found dark matter particles in an abandoned iron mine in Northern Minnesota. Emphasis on the "may":
" When the CDMS-II team looked at the analysis of their latest run – after accounting for all possible background particles and any faulty detectors in their stacks – they were in for a surprise. Their statistical models predicted that they would see 0.8 events during a run between 2007 and 2008, but instead they saw two.
The team is not claiming discovery of dark matter, because the result is not statistically significant. There is a 1-in-4 chance that it is merely due to fluctuations in the background noise. Had the experiment seen five events above the expected background, the claim for having detected dark matter would have been a lot stronger. "
Unable to prove that it is or isn't evidence of dark matter, the team are working on creating equipment three times as sensitive to use in the same area next year.
source : http://www.newscientist.com/
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