The ALMA telescope: Illuminating astronomical discovery

ALMA image of the young star HL Tau and its protoplanetary disk. This best image ever of planet formation reveals multiple rings and gaps that herald the presence of emerging planets as they sweep their orbits clear of dust and gas. Image courtesy ALMA (NRAO/ESO/NAOJ); C. Brogan and B. Saxton (NRAO/AUI/NSF).

We're used to the night sky, with its twinkling stars and bright moon. We're used to looking up at it and identifying the Big Dipper, the Orion Nebula, and maybe even a planet or two. But that's the ‘hot’ universe — the one illuminated by starlight. It's an interesting place, but there's a lot more going on that we can't see. Far beyond the reach of starlight, new stars are forming, new planets are being born, and incredibly distant galaxies are lurking in cold darkness.

We can't see them, but ALMA can. ALMA (the Atacama Large Millimeter/submillimeter Array) is the most sophisticated telescope in the world, both in its technical complexity and its capabilities. ALMA emerged after nearly 30 years of careful planning, design, and construction by the National Radio Astronomy Observatory (NRAO) through the US National Science Foundation, the National Astronomical Observatory of Japan (NAOJ), and the European Southern Observatory (ESO).

Built at an altitude of 16,500 feet above sea level on a plateau in northern Chile, ALMA is made up of 66 individual pieces that operate together as a single instrument. Each antenna is outfitted with a series of receivers, and each receiver is tuned to a specific range of wavelengths on the electromagnetic spectrum.  The antennas can be moved closer together or farther apart for different perspectives — like the zoom lens of a camera. The result is magnificent, never-before-seen imagery of deepest, darkest space. A recent test of ALMA's capabilities for seeing fine detail resulted in the best image ever captured of planets in formation around an infant star.

"The image ALMA created is really striking," says Charles Blue, public information officer for NRAO. "It shows a disk of gas and dust with very clear ring structures on it, revealing that planetary bodies are actually forming there now. When astronomers first saw it, they thought they were looking at a simulation. It was just that good."

Getting a single image from 66 different telescopes is the job of the Correlator, a supercomputer designed to do the heavy lifting for ALMA. The Correlator combines the signals from pairs of antennas, all of which add up to a finely detailed image of something much bigger. Once the Correlator's work is done, the data is sent to more traditional computers, where a specially designed software application further reduces the data to render information and images astronomers can use in their research.

ALMA has already aided in some groundbreaking discoveries. One such breakthrough came from supernova 1987A. Astronomers have long suspected that supernovas (exploding stars) are the primary source of the ubiquitous dust that litters galaxies, but direct evidence of that was hard to come by before ALMA. With ALMA, they were able to look inside the remains of supernova 1987A and see the dust forming.

ALMA has also been helpful in unexpected ways. When the New Horizons spacecraft needed a guiding hand to get to Pluto for a closer look, the US National Aeronautics and Space Administration (NASA) called ALMA into service. ALMA was able to take precise measurements of Pluto's location and orbit to help NASA scientists make the appropriate course corrections to get there.

For astronomers, ALMA is a unique and powerful resource. "Instead of taking snapshots of very distant objects, like 'normal' telescopes, it's more like being right there," says NRAO astronomer Alison Peck. "We can measure the depth so that we get a real 3D image, and we can measure the abundance of molecules, so it's like having these astronomical objects right here in a chemistry lab to study."

ALMA is also an incredible timesaver. Taking observations can be time consuming and quite daunting. But ALMA can make the necessary observations and wrangle the data much faster than a typical telescope, which opens the potential for a lot more scientific discovery.

ALMA's final antenna was installed earlier this year. Even before having the full complement of antennas, ALMA had already probed the mysteries of the Boomerang Nebula — the coldest place in the universe; taken remarkably detailed observations of supermassive black holes gobbling up matter and converting it to jets of particles and energy; and found monster starburst galaxies.

"ALMA is just beginning," says Blue. "It's just getting up to its full capabilities. It will change what we understand about our place in the universe, how planets formed, and possibly how conditions for life evolved elsewhere in the universe. It's exciting to talk about what it's done, but that's really only with a fraction of its capabilities. Right now is when we're going to see the really exciting discoveries start to happen."

- Amanda Aubuchon