A spectacular image of a dense gas cloud forming a generation of new stars has been captured on the official opening of the most complex observatory on Earth. The picture marks the first scientific result from the Atacama Large Millimeter/submillimeter Array (ALMA), a groundbreaking new facility which will probe the darkest, coldest and furthest reaches of the universe and could even teach us how the Earth was formed.
The first image taken by ALMA telescope shows the collision of two galaxies known as the Antennae Galaxies, a pair of distorted colliding spiral galaxies about 70 million light-years away, in the constellation of Corvus (The Crow). This view combines ALMA observations, made in two different wavelength ranges during the observatory’s early testing phase, with visible-light observations from the NASA/ESA Hubble Space Telescope. Credit: ESO, Space Science Institute
When it is completed in 2013 the site will consist of 66 linked satellite dishes spread across 16km of desert, allowing space experts to probe the oldest parts of the cosmos, produce images of previously unseen stars and planets, and discover how solar systems like ours are created.
Visible-light observations from the ESO Very Large Telescope
ALMA:
Humanity’s most complex ground-based astronomy observatory, the Atacama Large Millimeter/submillimeter Array (ALMA), has officially opened for astronomers. The first released image, from a telescope still under construction, reveals a view of the Universe that cannot be seen at all by visible-light and infrared telescopes. Thousands of scientists from around the world have competed to be among the first few researchers to explore some of the darkest, coldest, furthest, and most hidden secrets of the cosmos with this new astronomical tool.
At present, around a third of ALMA’s eventual 66 radio antennas, with separations up to only 125 metres rather than the maximum 16 kilometres, make up the growing array on the Chajnantor plateau in northern Chile, at an elevation of 5000 metres. And yet, even under construction, ALMA has become the best telescope of its kind — as reflected by the extraordinary number of astronomers who requested time to observe with ALMA.
“Even in this very early phase ALMA already outperforms all other submillimetre arrays. Reaching this milestone is a tribute to the impressive efforts of the many scientists and engineers in the ALMA partner regions around the world who made it possible,” said Tim de Zeeuw, Director General of ESO, the European partner in ALMA.
ALMA observes the Universe in light with millimetre and submillimetre wavelengths, roughly one thousand times longer than visible-light wavelengths. Using these longer wavelengths allows 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.
ALMA is radically different from visible-light and infrared telescopes. It is an array of linked antennas acting as a single giant telescope, and it detects much longer wavelengths than those of visible light. Its images therefore look quite unlike more familiar pictures of the cosmos.
The ALMA team has been busy testing the observatory’s systems over the past few months, in preparation for the first round of scientific observations, known as Early Science. One outcome of their tests is the first image published from ALMA, albeit from what is still very much a growing telescope. Most of the observations used to create this image of the Antennae Galaxies were made using only twelve antennas working together — far fewer than will be used for the first science observations — and with the antennas much closer together as well. Both of these factors make the new image just a taster of what is to come. As the observatory grows, the sharpness, efficiency, and quality of its observations will increase dramatically as more antennas become available and the array grows in size.
The Antennae Galaxies are a pair of colliding galaxies with dramatically distorted shapes. While visible light shows us the stars in the galaxies, ALMA’s view reveals something that cannot be seen in visible light: the clouds of dense cold gas from which new stars form. This is the best submillimetre-wavelength image ever made of the Antennae Galaxies.
Massive concentrations of gas are found not only in the hearts of the two galaxies but also in the chaotic region where they are colliding. Here, the total amount of gas is billions of times the mass of our Sun — a rich reservoir of material for future generations of stars. Observations like these open a new window on the submillimetre Universe and will be vital in helping us understand how galaxy collisions can trigger the birth of new stars. This is just one example of how ALMA reveals parts of the Universe that cannot be seen with visible-light and infrared telescopes.
ALMA could accept only about a hundred or so projects for this first nine-month phase of Early Science. Nevertheless, over the last few months, keen astronomers from around the world have submitted over 900 proposals for observations. This ninefold level of oversubscription is a record for a telescope. The successful projects were chosen based on their scientific merit, their regional diversity, and also their relevance to ALMA’s major science goals.
“We are living in a historic moment for science and particularly for astronomy, and perhaps also for the evolution of humanity, because we start to use the greatest observatory under construction at the moment,” said Thijs de Graauw, Director of ALMA.
One of the projects chosen for ALMA Early Science observations was that of David Wilner from the Harvard–Smithsonian Center for Astrophysics in Cambridge, Massachusetts, USA. Wilner said, “My team hunts for the building blocks of solar systems, and ALMA is uniquely equipped to spot them.”
His team’s target is AU Microscopii, a star 33 light-years away that is only 1% of the age of our Sun. “We will use ALMA to image the ‘birth ring’ of planetesimals that we believe orbits this young star. Only with ALMA, however, can we hope to discover clumps in these dusty asteroid belts, which can be the markers of unseen planets.” Wilner and his team will share their data with a European team who also requested ALMA observations of this nearby, dust-ringed star.
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