Even before the Atacama Large Millimeter/submillimeter Array (ALMA) was inaugurated this week, it was already rewriting history with observations showing that a stellar "baby boom" took place much earlier than previously thought. But the pre-inauguration announcement isn’t a reflection that the ALMA team didn’t get to enjoy the official ceremony – like the first images released in 2011, the observations were taken while ALMA was still under construction.
Made up of 54 dishes with diameters of 12-meters (39 ft) and 12 smaller antennas with diameters of 7-meters (23 ft), the array’s 66 antennas can be arranged in different configurations, with the distance between antennas able to range from 150 m to 16 km. Radiation from space is collected by the antennas, which focus it onto a receiver so the signals can be combined and processed by the ALMA Correlator supercomputer.
With construction beginning in 2003 on the Chajnantor plateau in the Atacama desert of northern Chile at an altitude of 5,000 meters (16,400 ft) above sea level, this week’s inauguration marked the completion of all ALMA’s major systems and signaled the project’s transition from construction to a fully fledged observatory. Assembly of the 66 antennas that make up the giant telescope’s full array was recently completed, although a final batch of seven is currently undergoing testing before entering into service.
Although still only partially finished, ALMA began scientific observations in the second half of 2011. Even before it becomes fully operational, ALMA is already demonstrating its unrivaled sensitivity. Using a partial array of 16 antennas, an international team of researchers captured light at wavelengths around 3 millimeters from 26 distant, dusty, star-forming galaxies.
They were surprised to find that these galaxies are even further away than expected, indicating that, on average, the most intense bursts of starbirth occurred 12 billion years ago, when the Universe was just under two billion years old. This baby boom is a billion years earlier than was previously believed.
Additionally, two of the galaxies observed are the most distant of their kind ever seen, with light from them emitted when the Universe was just one billion years old. Water was also one of the molecules detected from one of these two galaxies, making it the most distant observations of water ever achieved. The observations will be detailed in a set of papers to appear in the journal Nature and in the Astrophysical Journal.
While ALMA’s observations were enough to measure the distances for the majority of the galaxies, a few required the ALMA data to be combined with measurements from other telescopes, including the Atacama Pathfinder Experiment (APEX) and the ESO Very Large Telescope.
Even greater things are in the offing now that ALMA’s complete 66-antenna array is complete. Constructed at a cost of around US$1.4 billion in a partnership between Europe, North America and East Asia in cooperation with Chile, ALMA is expected to uncover details about the birth of stars, infant galaxies formed in the youth of the Universe, and planets coalescing around distant suns. It will also be used to measure the distribution of molecules – including many considered essential for life – that form in interstellar space.
ALMA will hold the title of the world's largest ground-based telescope until 2024, when it will be superseded by the Square Kilometre Array (SKA) being built in South Africa and Australia that will have a resolution 50 times that of ALMA.
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