All About ALMA, the Giant Radio Telescope Featured in 'Nostalgia for the Light'

“I tell myself we are all part of a current, of an energy, a recyclable matter, like the stars that must die so that other stars can be born, other planets – a new life.”
– Valentina Rodriguez in Nostalgia for the Light

In his documentary Nostalgia for the Light, Patricio Guzmán takes the viewer to many of the major observatory sites in Northern Chile’s Atacama Desert. However, most of the astronomers featured in the film speak about their work in relation to one telescope, the Atacama Large Millimeter/Submillimeter Array, or ALMA, located on the Llano de Chajnantor plateau in northeastern Chile near the Bolivian border.

The word “telescope” conjures images of a long, skinny metal tube with lenses on both ends, but ALMA is an entirely different beast. When completed in the next year or so, ALMA will be composed of 66 radio telescopes – actually high-precision dish antennae operating at frequencies from 31 to 950 GHz, a range much wider than any other array. (The Karl Jansky Very Large Array in New Mexico is similar in concept, and uses 27 antennae.) But ALMA’s real power comes from using data from the telescopes together, via a process called interferometry, in effect acting as a single telescope as large as the distance between the farthest-separated dishes. (For more information about radio telescopes and interferometry, see the National Radio Astronomy Observatory’s introduction.)

The antennae can be moved from just 150 meters apart up to 16 km, allowing it to “zoom” in or out to observe different targets. When finished, ALMA will be able to observe certain details at 10 times better resolution compared to the Hubble Space Telescope.

Although ALMA is only about 60 percent finished, it is already active and making significant contributions to science. Observations made in 2011 (with just 12 antennae) were combined with Hubble Space Telescope data to produce a gorgeous composite image of the Antennae Galaxies (aka NGC 4038 and NGC 4039) below.

Seeing the otherwise invisible gas clouds in these galaxies helps us understand the patterns of star formation we can see in visible light, and will help in guiding future observations of this tumultuous galactic merger. While ALMA will eventually produce images hundreds of times sharper, the image is, according to the European Southern Observatory, “the best submillimeter-wavelength image ever taken of the Antennae Galaxies.”

The Antennae Galaxies are 63 million light years away. We see them today as they were just after the K-T mass extinction that ended the era of the dinosaurs.

In this composite image with data from ALMA and Hubble, two galaxies are seen colliding with one another. The blue and white parts of this image are the visible light observations from the Hubble Space Telescope, while the red, pink and yellow light comes from ALMA, which can see beyond the visible spectrum to show the gas clouds from which new stars form. (You can compare both the images at the European Southern Observatory site.)

Very recently, ALMA provided the amazing image below of a dying star in the southern constellation Sculptor. Astronomers were looking at a shell of gas blown out from the star during a “thermal pulse event.” What they found, using only 20 ALMA antennae, was a surprise to everyone: an unseen and previously hidden companion star was carving spiral patterns in the shell. When the discover was announced, it was the first object of its type to be observed and it offers new insight into how stars evolve.

The light we receive from R Sculptoris, a neighbor in our own Milky Way galaxy, left at the beginning of Europe’s Middle Ages. It is a relatively close 1,500 light years away, but ALMA will eventually look billions of light years away, billions of years into the past.

On the high plain of Chajnantor, archaeologists of the skies see past events etched into the ejected shells of stars, the distorted shapes of colliding galaxies, and the mesh of galaxies condensing from the remnants of the Big Bang. ALMA’s achievements are exciting and its promise is tremendous, but there is another history concealed. Down below, others are trying to discover Chile’s history, etched into the desert itself, to remember and commemorate a past that many of their fellow citizens are trying to forget.

Jonathan Kade is an electrical and computer engineer by education, a software developer by trade, and an amateur astronomer by avocation. He is a member of the Warren Astronomical Society [http://www.warrenastro.org/was] near Detroit, Michigan.