Leak suggests cosmic study was wrong

The BICEP2 telescope studied a small patch of sky in detail above the South Pole

Scientists who claimed last year to have found a pattern in the sky left by the super-rapid expansion of space just fractions of a second after the Big Bang were mistaken.

The signal had been confounded by light emission from dust in our own galaxy.

This appears to be the conclusion of a new study involving the US-led BICEP2 team itself.

A summary of the paper was briefly posted on an official French website, but then pulled.

The information was not supposed to have been released until early next week, when the actual paper itself would have been put up on the Arxiv pre-print server. Its ultimate peer-reviewed destination was likely to be the journal Physical Review Letters where previous BICEP papers have been published.

A determination that BICEP2 was mistaken in its observations is not a major surprise.

The team itself had already made known its reduced confidence in the detection. But the new paper is significant because it is co-authored by scientists from the Planck Consortium – researchers operating a European Space Agency satellite that had also been seeking the same expansion pattern.

It was on the website of one of that satellite’s instrument teams – its High Frequency Instrument (HFI) – that the outcome of the joint assessment was briefly leaked.

The BBC understands that some of this information was inaccurate, but that its broad thrust was correct.

All the joint effort could do – according to the removed summary – was put an upper limit on the likely size of the signal.

This will be important for those future experiments that endeavour to make what would be one of the great discoveries in science.

Issues of confusion

BICEP2 used an extremely sensitive detector in an Antarctic telescope to study light coming to Earth from the very edge of the observable Universe – the famous Cosmic Microwave Background (CMB) radiation.

It was looking for swirls in the polarisation of the light.

This pattern in the CMB’s directional quality is a fundamental prediction of inflation – the idea that there was an ultra-rapid expansion of space just fractions of a second after the Big Bang.

BICEP sought characteristic swirls in the polarisation of the Universe’s oldest light

The twists, known as B-modes, are an imprint of the waves of gravitational energy that would have accompanied the violent growth spurt that occurred almost 14 billion years ago.

But this primordial signal – if it exists – is expected to be extremely delicate, and a number of independent scientists expressed doubts about the American team’s finding as soon as it was announced in March 2014.

At issue are a couple of complications. One is an effect where a “false” B-mode signal can be produced on the sky by the CMB passing through massive objects, such as huge galaxies. This so-called lensing effect must be subtracted.

But the second and most significant issue is the confusing role played by foreground dust in our galaxy.

Nearby spinning grains can produce an identical polarisation pattern, and this effect must also be removed to get an unambiguous view of the primordial, background signal.

The BICEP2 team used every piece of dust information it could source on the part of the sky it was observing above Antarctica.

What it lacked, however, was access to the dust data being compiled by the Planck space telescope, which had mapped the microwave sky at many more frequencies than BICEP2.

This allowed Planck to more easily characterise the dust and discern its confounding effects. The Planck consortium agreed to start working with BICEP2 back in the summer.

The results of the joint assessment leaked by the French Planck HFI website would suggest that whatever signal BICEP2 detected, it cannot be separated out at any significant level from these other spoiling effects.

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

Article source: http://www.bbc.co.uk/news/science-environment-31058529#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa

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