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ALMA: Large Array Looks Through Dust To See Starbirth

ALMA Array from the Air Space Wallpaper
This space wallpaper shows an aerial view of the Chajnantor Plateau, located at an altitude of 5000 meters in the Chilean Andes, where the array of ALMA antennas is located.
Credit: Clem & Adri Bacri-Normier (wingsforscience.com)/ESO

The Atacama Large Millimeter/submillimeter Array (ALMA) is a telescope array in Chile that includes 66 receivers. The array is located on the Chajnantor Plateau in the Atacama Desert and bills itself as "the largest astronomical project in existence."

ALMA is able to peer through the dust that obscures planetary systems under construction, or to look back at stars and galaxies that formed in the early days of the universe and emit their radiation in millimeter light — waves that are about 1,000 times longer than visible-light wavelengths.

Although there are other observatories that can do the same thing, what distinguishes ALMA is its sheer size and number of receivers. Working together, they provide more sensitivity in astronomical observations and allow astronomers to look at the universe in high definition.

ALMA View of Molecular Gas in NGC 1433
This image from ALMA shows the distribution of molecular gas close to the supermassive black hole at the centre of the galaxy NGC 1433. Image released Oct. 16, 2013.
Credit: ALMA (ESO/NAOJ/NRAO)/F. Combes

Concept combinations

ALMA can be viewed as an amalgamation of three separate projects under conception: the Millimeter Array (MMA) of the United States, the Large Southern Array (LSA) of Europe and the Large Millimeter Array (LMA) of Japan. Through conversations between researchers, scientists concluded it would be easier to collaborate on one large project rather than creating several smaller ones.

The first large milestone occurred in 1997, when the European Southern Observatory (ESO) and the National Radio Astronomy Observatory (NRAO) agreed to merge MMA and LSA, a move they formalized in 1999. The ALMA agreement between the entities was subsequently signed in February 2003, with Japan joining in 2004.

Rhe ALMA partners negotiated an agreement with the country to build ALMA at Llano de Chajnantor, a high-altitude site that would make it easier to observe the cosmos because the atmosphere is thinner there. In exchange, Chile received 10 percent observing time and additional "cultural, educational and production activities," according to ALMA. The $1.3 billion cost was borne principally by North America and Europe, with Japan close behind.

Contracts for the antennas were awarded in 2005, with the first antenna coming to Chile in 2007. As antennas arrived and were checked for health and interferometry capabilities, ALMA put out a call for the first science observations. Antennas began moving to Chajnantor in 2009, and observations began with a partially completed ALMA in 2011. The 66th and final antenna was accepted in 2013.

ALMA 3D Visualization of NGC 253 wallpaper
This space wallpaper shows a view of a three-dimensional visualization of gas in the nearby starburst galaxy NGC 253 (The Sculptor Galaxy) as observed by the ALMA radio telescope in Chile.
Credit: ALMA (ESO/NAOJ/NRAO)/Erik Rosolowsky

Science capabilities

ALMA's extreme altitude is an aid in performing observations. Its highest receivers are about 16,500 feet (5,000 meters) above sea level, far above much of the atmosphere and water vapor that can make it hard to see what's in the sky. Astronomers work in a facility at 9,500 feet (2,900 m), where they receive supplemental oxygen if they're going to stay awhile.

The 66 antennas can be arranged in many different configurations, ranging from very close together to quite spread apart. At its greatest, the receivers can be moved as far as 9.9 miles (16 kilometers) apart. Each telescope receives information individually, then transmits the data to a supercomputer that combines the information to trace the signal direction — a high-tech version of how human ears combine to locate a sound.

This technology allows astronomers to look at three principal questions, according to ALMA's website: the nature of the universe's first stars and galaxies, how planets and stars come together, and what the chemistry is of the gas and dust clouds that may eventually collapse to form planets and stars.

"Many other astronomical specialties also will benefit from the new capabilities of ALMA," the website added, such as the ability to "map gas and dust in the Milky Way and other galaxies, investigate ordinary stars, analyze gas from an erupting volcano on Jupiter's moon, Io [and] study the origin of the solar wind."

Infographic: How the huge ALMA radio telescope works.
Made up of dozens of small radio telescope dishes, the ALMA telescope will be one of the most powerful in the world. See how the giant ALMA radio telescope works in this Space.com infographic.
Credit: Karl Tate, Space.com Infographics Artist

Early results

The first image from ALMA was a combined view of the Antennae Galaxies, which are about 75 million light-years from Earth. Another early image pierced dust surrounding the Centaurus A galaxy to show its bright center. The telescope is also capable of producing three-dimensional visualizations of gas, such as the image above of NGC 253 (the Sculptor Galaxy) released in 2013.

One of ALMA's most prominent finds was announced in 2014 from examining a famed supernova remnant — the leftovers of supernova 1987A — and uncovering dust spewing in the area.

"We have found a remarkably large dust mass concentrated in the central part of the ejecta from a relatively young and nearby supernova," astronomer Remy Indebetouw, of NRAO and the University of Virginia, said in a statement. “This is the first time we've been able to really image where the dust has formed, which is important in understanding the evolution of galaxies."

A baby star was captured on camera in 2013 showing the youngster blasting out starstuff at 84,477 mph (144,000 kph). Once the material crashed into the surrounding gas, it produced a glow. This could provide some clues as to how the sun came together, astronomers said at the time. "The sun is a star, so if we want to understand how our solar system was created, we need to understand how stars are formed," Héctor Arce, the lead author of the Astrophysical Journal study, said in a statement.

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