By Govert Schilling
Just over a week ago, at three miles above sea level in the Chilean Atacama desert, Atacameño indians offered gifts to Mother Earth in a traditional ceremony to bless a decidedly modern object: the Atacama Large Millimeter/submillimeter Array (ALMA). Four days later, on March 13, the largest-ever ground-based astronomical observatory was officially inaugurated. “ALMA is now a reality, and not a fairy tale anymore,” said Dutch astronomer Thijs de Graauw, the project’s director. ALMA (Spanish for "soul") consists of 66 antennas, most of them 40 feet across. They are equipped with sensitive receivers to detect millimeter and submillimeter waves from space – radiation in between radio waves and infrared light. This relatively long-wavelength radiation is emitted by the coolest objects in the Universe, such as the dark molecular clouds that spawn new stars and planets. What's more, interstellar molecules, including complex hydrocarbons and other molecules necessary for life, can only be identified using this type of radiation. Cosmic millimeter and submillimeter radiation has never been observed in much detail before, so astronomers all over the world have eagerly anticipated the ALMA inauguration.
The relative elevations of some famous astronomical observatories, including ALMA, for comparison. Credit: NRAO/AUI/NSF Because such radiation is absorbed by atmospheric water vapor, however, ALMA has to be extremely high up. The Chilean Chajnantor plateau, east of the backpacker township of San Pedro de Atacama, is perfect: It’s extremely high and the air is extremely dry. As an added bonus, the scenery is stunning: the plateau is surrounded by volcanoes. The downside, of course, is that working at this altitude, with half the normal amount of oxygen, is prohibitive. One day before the inauguration, many visitors experienced dizziness, nausea and loss of concentration. Some weren’t even allowed to visit the "high site" for medical reasons like hypertension. “This is the second-highest man-made building in the world,” says head of engineering Michael Thorburn. “The Tanggula railway station in Tibet is slightly higher – but we have more computing power,” he joked.
A Google Maps for space
Preliminary science operations began over a year ago, when only half of the 66 antennas were operational. French astronomer Pierre Cox, who will be ALMA’s new director as of April 1, says now expectations run high, and rightfully so. “We are in the middle of a renaissance of millimeter and submillimeter observations,” he says. For one thing, ALMA will reveal very distant starburst galaxies, where the star formation rate is hundreds of times as high as in our own Milky Way. By changing the configuration of the array – the antennas can be close together or spread out over an area 10 miles wide – astronomers can use ALMA as a "zoom telescope," says de Graauw. In its compact configuration, ALMA has a bigger field of view, but lower resolution. In contrast, the extended configuration provides a much sharper vision than the Hubble Space Telescope, but only for small areas in the sky. “It’s like zooming in on a city in Google Earth, revealing individual houses,” says astrochemist Ewine van Dishoeck of Leiden University.
A close-up of one of ALMA's antennas. Credit: research.gov ALMA will also shape our understanding of the formation of stars and planets, hopefully observing planet formation in action. ALMA will also be able to study the distribution of organic compounds in the clouds of gases – the raw materials for planets – surrounding newborn stars. Sugar and water have already been detected in these kinds of disks. Says van Dishoeck: “If we find the right molecules, we can go to the biologists and say, 'Here are the ingredients – can you make life out of it?'”
Long in the making
ALMA is a one-billion-dollar international project with contributions from North America, Europe and Eastern Asia. At the inauguration ceremony on Wednesday, representatives of the three participating agencies expressed their excitement about the facility's completion. Tim de Zeeuw, director-general of the European Southern Observatory (ESO), told the audience how surprised he was to read about an ALMA-like observatory in the science fiction novel The Inferno by Fred and Geoffrey Hoyle, published in 1973, just after the discovery of the first interstellar molecules. Chilean president Sebastián Piñera added that the local Atacameños must have been pretty visionary too, when, many centuries ago, they chose the name Chajnantor for the high plateau where ALMA is now located. “Chajnantor means ‘point of observation,'” he said, “so they knew it.” For soon-to-be director Cox, the biggest challenge will be to lead ALMA into a whole new phase. “Construction will make place for operations,” he says. “My job is to turn ALMA into a real observatory.” And the observatory’s future looks bright. During its projected operational lifetime of thirty years, the array can be constantly upgraded by using more sensitive receivers, or expanded by adding more antennas. Looking back at the design and construction phase of ALMA, head of engineering Michael Thorburn remarked “It has been quite a journey.” But the real journey, of course, is only just beginning. Govert Schilling is a freelance astronomy writer in the Netherlands. He attended the ALMA inauguration at the invitation of the European Southern Observatory.
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seconds: ALMA’s accuracy in synchronizing the signals from the various antennas 0.35 millimeters: the shortest wavelength that ALMA can observe 1 astronomical unit (Sun-Earth distance): ALMA’s spatial resolution in nearby star-forming regions 4 kelvin: the temperature of the ALMA receivers, obtained through cryogenics 7 millimeters: the longest wavelength that ALMA can observe 7 meters: the diameter of twelve of the sixteen Japanese antennas (the other four are 12 meters in diameter, just like the 25 American and the 25 European antennas) 10: the number of wavelength bands in which ALMA will eventually be able to observe (some are still under construction) 16 kilometers: the equivalent diameter of the telescope that is synthesized by combining the signals of the 66 ALMA antennas 25 micrometers (about the width of a human hair): the surface accuracy of the ALMA dishes 28: the number of wheels of the two 130-ton ALMA transporters 30 years: the minimum projected operational lifetime of ALMA 54: the number of antennas currently in operation at the Chajnantor plateau 66: the total number of ALMA antennas (25 from North America, 25 from Europe, 16 from Eastern Asia) 100 metric tons: the weight of a single ALMA antenna 192: the number of foundations at which ALMA antennas can be positioned 5,000 meters: the altitude at which ALMA is located 7,000 square meters: the total collecting area of the ALMA array 134,000,000: the number of processors in the ALMA correlator that combines the signals from the 66 antennas 1,000,000,000 dollars: the estimated total project costs of ALMA 17,000,000,000,000 flops: the number of floating point operations per second that the ALMA correlator carries out
