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Infrared view of the
Unicorn wows

by Nicky Guttridge
Posted: 08 October 2010

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A new image taken by the VISTA telescope shows a remarkable landscape within the constellation of the Unicorn, only visible in the infrared.

Star formation region Monoceros R2, as seen by the VISTA survey telescope at ESO's Paranal Observatory. Image: ESO/J. Emerson/VISTA. Image: Cambridge Astronomical Survey Unit.

The image reveals glowing tendrils of gas, dark clouds and young stars. The star-forming region within the constellation of Monoceros – otherwise known as the Unicorn – is almost completely obscured by interstellar material and dust when viewed in the visible part of the spectrum, but is unmistakable in the infrared. The image was taken from the Paranal Observatory in northern Chile using the UK-designed and built Visible and Infrared Survey Telescope for Astronomy (VISTA).

The region of the sky imaged is known as Monoceros R2, a substantial stellar nursery embedded within a dark cloud in the constellation of Monoceros. By sight it appears to be close in the sky to the Orion nebula, but it is in fact almost twice as far from the Earth, 2700 light-years away. In the visible spectrum, the grouping of hot stars creates a blue hue, with the outer layers of the molecular cloud scattering and reflecting the light. However, the new-born stars are not observable as the visible and ultra-violet light they emit is strongly absorbed by the cloud. The most massive of these young stars are no more than 10 million years old.

“When I first saw this image I just said, ‘Wow!’ I was amazed to see all the dust streamers so clearly around the Monoceros R2 cluster, as well as the jets from highly embedded young stellar objects. There is such a great wealth of exciting detail revealed in these VISTA images,” says Jim Emerson of Queen Mary, University of London and leader of the VISTA consortium.

Extracts from the VISTA image of the Monoceros R2 star forming region. Image: ESO/J. Emerson/VISTA. Image: Cambridge Astronomical Survey Unit.

The image pierces through the dust cloud to reveal the loops, folds, filaments and other structures present that have been sculpted by the particle winds and radiation caused by the hot young stars. It was created from three exposures of different regions of the near-infrared spectrum. The low temperatures and high densities present in a cloud like Monoceros R2 create ideal conditions for molecules to form which can emit very strongly in the infrared, such as hydrogen. Many of the pink and red structures visible in the image are thought to be due to glowing molecular hydrogen outflows from the young stars.

The core of Monoceros R2 is dense – no more than 2 light-years across – and packed with massive young stars, as well as a cluster of infrared sources such as newborn stars still surrounded by material and dusty discs. This region is shown at the centre of the image, which displays reddish features and a much higher concentration of stars than shown in other parts of the image. The rightmost of the three central clouds is known as NGC2170, the brightest reflection nebula in the region, within which hundreds of massive stars are forming.

As interstellar material is opaque to visible light, infrared and radio observations are significant in exploring active star-forming regions to understand the earliest stages of stellar evolution. VISTA is a very large telescope capable of infrared studies, currently dedicated to surveying the sky. It is equipped with a sensitive camera, a mirror of over 4 metres in diameter, and a huge field of view – at the distance represented in the image, the width of this field translates to about 80 light-years. This makes it a useful instrument in gathering deep, high-resolution images. Its aim is to map the southern sky, gathering some 300 gigabytes of information per night which will then be analysed and examined using other instruments.

Professor Ian Robson, Head of the Science and Technology Facilities Council’s UK Astronomy Technology Centre which manages the VISTA project, says that this image “is just the tip of the iceberg of the wealth of new science being discovered as VISTA continues its mission of surveying the infrared sky.”

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