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Esa's Planck telescope finds value in 'reject' data

26 April 10 16:47 GMT
By Jonathan Amos
Science correspondent, BBC News

The gaseous and dusty fabric of our galaxy is illuminated in new images captured by Europe's Planck telescope.

The pictures reveal features of the Milky Way that are unseen by most other space observatories, say scientists.

Remarkably, these images are just byproducts for Planck, which must filter out much of the light it detects to get at its primary target.

That target is a relic radiation emitted in the first few hundred thousand years after the Big Bang.

This so-called Cosmic Microwave Background (CMB) fills the entire sky and retains fundamental information about the age, contents and structure of the cosmos.

On one level, therefore, Monday's release represents "rejected" data - although Planck scientists stress there will be many researchers for whom this information will still hold high value.

"For the primary CMB, we want to remove all the galactic emission - but it's an important part of the science case for Planck that you can also learn a lot about the galaxy from that data," Planck team-member Professor George Efstathiou told BBC News.

Cold clumps

The pictures illustrate "the stuff" that sits between the stars - the great clouds of dust and gas that billow about in space, aggregating in some places to form stars and dispersing in others as they are pushed about by the pressure of starlight.

In one picture of the Orion Nebula, Planck's instruments see concentrated fronts of material where stars are actively forming. In a second image of a far more sedate region of space in the Perseus Constellation, the structure and distribution of this material looks much more diffuse.

Planck's super-sensitive instruments work at a range of very long wavelengths, in the radio part of the electromagnetic spectrum.

Scientists probe these different wavelengths to highlight particular features.

At the lowest frequencies, the telescope sees the emission given off by electrons accelerating through the magnetic fields of our galaxy.

At intermediate wavelengths, the light detected by Planck is dominated by gas that has been excited by newly formed stars.

And at the highest frequencies in its range, the observatory maps the emission coming from the coldest clumps of dust that trace the matter falling in on itself to form new stars.

All of this information provides useful insight on the complex processes that go into sculpting our galaxy.

"The two highest frequency channels on Planck are really there to study dust; they were put on to allow galactic science. Those are the primary channels for detecting cold star-forming core regions," said Professor Efstathiou.

"We don't know that much about dust emission from the galaxy because, at these wavelengths, the atmosphere is opaque. They are absorbed by water vapour. That's why you go into space with a mission like Planck."

Big prize

Planck's chief objective, however, is to map the Cosmic Microwave Background.

This only becomes apparent when all the "contaminating" light that beautifully illuminates the latest pictures is stripped out.

Planck should complete its first all-sky survey of the CMB within weeks. Recently agreed funding should see the telescope eventually acquire at least four-times coverage.

The project team will then need time to analyse all the data and assess its significance. A formal release of CMB maps and scientific papers is expected at the end of 2012.

Past pioneers in the study of the Cosmic Microwave Background have earned a clutch of Nobel Prizes, and there is great hope that the super-sensitivity of Planck will advance the field considerably.

Planck is a mission of the European Space Agency. It was launched on 14 May last year. Its observing station is sited 1.5 million km from Earth on its "night side".

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