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Gravitational waves pulverized


Contrary to what was announced last spring, there is still no firm evidence of the presence of “ways B” primordial – dating back to the Big Bang – the polarization of the CMB. This is the conclusion, after months spent side by side to analyze the data, the team of ESA’s Planck satellite and telescope Antarctic BICEP2.
I thought it was love … and instead, as in the play of Massimo Troisi, for cosmologists Telescope Antarctic BICEP2 expectations have not been kept. Where they believed he had glimpsed, in those lovely curls polarized the cosmic background radiation called “B-modes”, nothing less than the imprint of primordial gravitational waves, in all probability there was nothing but dust. To be more precise, due to the galactic dust emission.

Planck visualization showing dust temperature as color, with magnetic polarization shown as the relief map.

mappa-planck-bicep

Credit: ESA/Planck Collaboration

After nearly one year after the March 17 aroused, around the world, a voice comparable to that of the discovery of the Higgs boson, so comes the moment of disappointment. To sanction officially the end of the dream, an unpublished work “four hands” of the two teams once rivals – the fact of BICEP2 one hand, and the mighty team of scientists at the Space Telescope Planck other – but few months collaborators to extract the best from the potential of the two instruments. Work early today not without some awkwardness communicative – probably the official announcement was scheduled for next week – and already submitted to the journal Physical Review Letters.
In reality, the dream was shattered for some time. The rumors of possible contamination by so-called foregrounds (just as the galactic dust) had started almost immediately. And last September are the first maps produced by Planck polarized dust emission at high galactic latitudes, from which maps already emerged clearly as those who had believed BICEP2 regions were relatively clean, on closer inspection, rather “dusty” also .
But the news, then? Where is the news? The news there is, and it is very good news: and that is that the twinning between the two teams, there was, and has produced an important result, as it may have disappointed those who hoped for a confirmation of the observation of gravitational waves. A fine example of how it should work science. Here’s how John Kovac – Manager BICEP2 of Harvard University, then one of the main protagonists of the “offending” last spring – has retraced the whole story: “When traced for the first time the signal We entrusted us with the models d ’emission of galactic dust available at that time. Models that seemed to indicate that the region of the sky choice for observations presented a contribution in the polarization of the dust were far below the signal measured by us. “In other words, having observed an area considered relatively untouched by the dust, the team BICEP2 had interpreted the signal as the probable cosmological origin.The basic problem of BICEP2 is that – as well as the other Antarctic experiment that had collected data on polarization in the same area of the sky, the Keck Array – working on a single microwave frequency, 150 GHz. This precludes the possibility to distinguish between foreground emissions and emissions of background. This operation is, instead of Planck’s reach, having observed that the entire sky on nine different frequency channels (seven of which with detectors sensitive to polarization) is able to separate from the signal cosmological the various contributions of the galaxy, both to high frequency (dust, detectable by the instrument HFI) that at low frequency (emission by electrons and dust grains, detectable by the instrument LFI). Here is the team of Planck and BICEP2 have decided to join forces also to take advantage of the obvious complementarities between the two instruments: the ability of the ESA satellite to observe the entire sky on multiple frequencies on the one hand, and the greater sensitivity of the experiments from the ground on the other.

The conclusions made public today, we said, will play for some a bit ‘disappointing. “We have shown that, once removed the issue of galactic dust,” says Jean-Loup Puget fact, the French Institut d’Astrophysique Spatiale, responsible for the instrument HFI Planck, “proof of detection” modes B “primordial is not so solid. Unfortunately, therefore, we cannot confirm that the signal really represents an imprint of cosmic inflation. “

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