16 Jul 2007

Akari maps warm universe in exquisite detail

The entire sky in infrared light as seen by AKARI

The entire sky in infrared light as seen by AKARI

A team of Japanese and European astronomers - including some from The Open University - have mapped the whole sky at infrared wavelengths for the first time in two decades. The new map, produced using the AKARI surveyor, is far sharper than its most recent predecessor, completed by the IRAS satellite back in 1984.

Team member Dr Chris Pearson from the Japan Aerospace Exploration Agency (JAXA) and European Space Agency presented the results at the From IRAS to Herschel and Planck conference at the Geological Society in London. The meeting was held to celebrate the 65th birthday of Royal Astronomical Society President Professor Michael Rowan-Robinson.

The AKARI satellite uses a telescope with a 68.5cm diameter mirror to detect radiation at near-, mid- and far-infrared wavelengths. Many of the cooler objects in the Universe emit infrared radiation that penetrates dust and gas much more readily than visible light, so telescopes like AKARI are able to image objects like forming stars and the centres of galaxies.

AKARI was launched on 21 February 2006 from the Uchinoura Space Center in southern Japan. On current projections, the liquid helium it uses to keep the detectors cold will last until at least 9 September 2007, giving the primary mission a lifetime of about 550 days. Scientists may then extend its life using mechanical coolers to allow observation of sources emitting near-infrared radiation to continue.

The new high-resolution map is assembled from thousands of different images made as the AKARI satellite orbited the Earth gradually scanning the entire sky. One of the released images shows the whole sky as seen by AKARI, with the plane of our Galaxy (the Milky Way) visible as a bright stripe running from left to right. The bright region in the centre of the image is the material surrounding the galactic centre, thought to harbour a giant black hole.

At the lower right of the all-sky image is the Large Magellanic Cloud, a small galaxy that orbits the Milky Way at a distance of about 160,000 light years (or 1.5 million million million km). AKARI images clearly show the regions in this and the other galaxies where stars are forming at a vigorous pace.

Another set of figures shows the region of the sky in the direction of the constellation of Orion, familiar to northern hemisphere observers in the winter months. One image is made with visible light whilst the other image shows the same region depicted using the far-infrared emission detected by AKARI. In both images star-forming regions like the Orion, Rosette and Horsehead nebulae (clouds of gas and dust) are clearly visible. The infrared light from young stars in each nebula heats up their surroundings so much that these regions dominate the AKARI image. At the top right a giant circle of gas is all that remains of a series of explosions that took place when some of the most massive stars ended their lives, sweeping away the surrounding dust and gas.

A fourth image shows the far-infrared view of the constellation of Cygnus, a part of the sky best seen in the northern summer. Bright spots mark other regions of star formation, alongside dark voids cleared by the winds from nearby massive stars. The Milky Way runs from top left to bottom right.

Chris Pearson commented on the new images: "The first comprehensive result from the AKARI mission's All-Sky Survey is an astoundingly beautiful map of the entire sky. With this image we can see in explicit detail the structure of our own galaxy and the Universe beyond. We are now looking forward to the next images that will show the sky at longer infrared wavelengths."

Open University scientist and collaborator Dr Stephen Serjeant added, "I'm delighted with this beautiful image of the whole sky. The images of Orion show how strikingly different the sky looks in infrared light. This is our first step towards a comprehensive map of the birth of stars and galaxies in the Universe."

AKARI will continue to scan the sky at six independent wavelengths until the expiration of the on-board 170 litres of liquid helium, all the while gradually building up a multi-colour map of the entire sky. From these observations, detailed catalogues will be created with the aim of providing a complete census of the local infrared Universe. These catalogues will eventually be released to the global astronomical community. After the helium has expired AKARI will still have the use of its near-infrared cameras in the final phase of the mission that will last for a further year.

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