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Powerful new telescope array opens eyes on Universe
DR EMILY BALDWIN, REPORTING FROM THE ATACAMA DESERT, CHILE
ASTRONOMY NOW
Posted: 03 October 2011


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A crucial step for the world’s most powerful ground-based telescope array, the Atacama Large Millimeter/submillimeter Array (ALMA) took its first science observations this weekend, of the colliding Antennae galaxies.


Comparison of the millimetre and submillimetre light observations (left), made in two different wavelength ranges by ALMA during the observatory's early testing phase, with visible-light observations from the ESO Very Large Telescope. ALMA’s view reveals the clouds of dense cold gas from which new stars form. Image: ALMA (ESO/NAOJ/NRAO). Visible light image: ESO/Alberto Milani.

Currently comprising twenty working 12-metre antennas – the first image was constructed using sixteen – the final array, set for completion by 2013, will boast 66 telescopes. At a grueling 5,000 metres altitude on the Chajnantor plain of the Chilean Andes, ALMA is located at one of the highest and driest astronomical sites in the world, affording exceptional atmospheric conditions for making millimeter and submillimeter wavelength observations. These long wavelengths allow astronomers to study extremely cold objects in space, such as the dense clouds of cosmic dust and gas from which stars and planets form, as well as very distant objects in the early Universe, and the relic radiation left over from the big bang.

“We are exploring an extremely important part of the Universe, which was previously hidden,” Diego Garica-Appadoo, an ALMA astronomer said from the array’s control room yesterday.


A composite of the ALMA millimetre and submillimetre light observations and visible light Hubble data. Image: ALMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope.

The first image, taken on Friday and released today is part of the science verification phase, that is, to check that the array is working correctly and able to reproduce already well-studied objects. It depicts the Antennae galaxies, the site of an intergalactic smash-up between two spiral galaxies. During galactic crashes the stars themselves avoid collision, but if there are clouds of gas present these plough into each other, causing them to become compressed and triggering the formation of millions of new stars. While visible light images typical of the Hubble Space Telescope shows the stars in the galaxies, ALMA’s long wavelength eyes reveal the dense gas from which these new stars are born.

“What the ALMA image shows is exactly where the gas clouds are, which are still in the process of forming more stars,” Richard Hills, ALMA Project Scientist tells Astronomy Now. “Once the image has been studied in detail we will learn about the speeds at which the clouds are coming together, the size of the clouds the amounts of gas in the clouds – generally the nitty gritty of what actually happens when two galaxies collide.”


ALMA is located on the 5000 metres altitude Chajnantor plain of the Chilean Andes. Once complete, the antennas will be separated by up to 16km. Image: Emily Baldwin.

Once complete, the main array will comprise fifty 12 metre antennas, with a compact array made up of twelve 7-metre and four 14-metre antennas. The maximum separation of the antennas will be 16 kilometres, more than a thousand times the diameter of a single individual telescope within the array. Increasing the separation between the antennae will result in sharper images, while increasing the number of antennas linked up for any observation will provide more detailed images.

Observations in this early science phase will continue while the array is being completed; around 100 projects out of the 900 submitted by astronomers worldwide have been accepted for this phase, and will cover topics from the study of young stars and the hunt for water in their debris discs to provide insight into the formation of our own Solar System, to studies of the flaring episodes of the supermassive black hole that lurks in the centre of our Milky Way to learn more about its feeding habits as it consumes nearby material.

“Even now with just 16 antenna we are seeing things we haven’t been able to before, but even though we know what we want to study, it’s all the things that we don’t know are out there that are going to be the most interesting,” adds Garica-Appadoo.

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