A prospectus for public science communicators
Atacama Large Millimeter/submillimeter Array
The universe of the coming ALMA revolution
In the Atacama Desert, at an altitude of 5,000 meters, the greatest ground-based observatory in human history is taking shape. It is so vast and complex that a global coalition of scientists and engineers is needed to design and build it. A triumph of extreme engineering, and gateway to an unexplored frontier, it will answer deep questions as no other observatory can. ALMA is the Atacama Large Millimeter/submillimeter Array. Its story is waiting to be told. (By you).
Left: An artistâ€™s rendering of the ALMA Array in its extended configuration. Distances between antennas can exceed 16 kilometers. Credit: ALMA (ESO / NAOJ / NRAO)
Early Science in 2011
You will probably never visit Mars, but by visiting the ALMA site in the breathtaking Chilean Andes, you will have a good idea of how it looks like. For all its exotic qualities, this place is remarkably convenient to the comforts of civilization. The nearby town of San Pedro is becoming a popular tourist destination for nature and authenticity lovers.
Above: The San Pedro church. Credit: ALMA (ESO / NAOJ / NRAO)
Left: Chajnantor seen from the south. Credit: ALMA (ESO / NAOJ / NRAO), H.H.Heyer (ESO)
The incredible Atacama Desert
ALMA will observe invisible light naturally emitted by the universe at millimeterand submillimeter-wavelengths, a portion of the microwave region of the spectrum. Water vapor absorbs this light, hindering it from reaching the ground. ALMA’s high, dry location puts the telescope’s antennas above some 40% of the atmosphere and 95% (or more) of the water vapor compared to a typical sealevel location. Some mountaintops elsewhere are almost as good, but ALMA’s antennas need to be spread across miles of level ground; there are few such level plains in the world at 5,000 meters! From its site near the equator, ALMA can observe much of the universe. In addition, Chile has a thriving scientific community that welcomes cutting-edge research projects.
Left: An impressive view of the Chajnantor plateau with the Licancabur volcano on the far left. Credit: ALMA (ESO / NAOJ / NRAO), R. Bennett (ALMA)
The atmosphere above ALMA
The colors of light that our eyes can detect are but a thin sliver of the entire spectrum. The universe emits light in every invisible color, from radio waves to gamma rays, and studies conducted within each band of the spectrum contribute uniquely to our understanding. Only now has technology caught up with the dream of opening up a rich new vein of the spectrum to high-resolution exploration. Millimeter-wavelength light is a “sweet spot” for tomorrow’s astronomy because… It’s what half the light is. In addition to the cosmic microwave background (a nearly uniform glow from every part in the sky), the universe emits most of its light in two broad “humps” of color. We’ve been studying the first, visible light, for four centuries with optical telescopes. The second is centered on far-infrared colors that are blocked by Earth’s atmosphere and can be observed in high resolution using space-based observatories. Fortunately, ALMA, due to the incredible transparency and stability of the site where its located and careful choice of frequency bands, will be able to observe some of this light from the ground. It’s where the “cool stuff” is happening. Among the most profound mysteries in astronomy are the origins of things such as galaxies, stars, planets, and the molecules that seed life. ALMA will observe light emitted by cool-temperature objects in space, whether the invisible glow of dusty clouds just warming up as stars ignite deep within, or the spectral line codes of complex molecules that we don’t yet know are out there.
Left, above: Electromagnetic energy emitted by the universe since the formation of stars and galaxies. About half this light falls in the far-infrared and submillimeter spectral range. Below: The electromagnetic spectrum, from radio to gamma ray, with ALMA’s spectral sensitivity indicated.
ALMA’s portion of the spectrum of light
ALMA’s 12-meter and 7-meter diameter antennas are the most precise ever made. In the gusty winds and fluctuating day/night temperatures of the highaltitude desert they maintain perfect parabolic shapes to within a fraction of the thickness of a human hair. Pockets of water vapor drifting over the antennas distort the light waves coming from space. Uncorrected, this distortion would ruin ALMA’s ability to make high-precision observations. ALMA has two completely new ways of dealing with this problem. First, every ten seconds the antennas will very quickly pivot from the target they’re studying to look at a nearby known target in the sky. Measuring how much that object appears distorted, we can apply a correction to the image of the object being studied. The antennas will rapidly pop back and forth between observed target and “guide target” over and over again. Second, each antenna will be equipped with a radiometer that will continually measure the radiation being emitted by water vapor that is in the antenna’s line of sight. This will enable additional corrections to be applied to the observed signal. The combined effect of these techniques will be to greatly reduce measurement errors caused by water vapor, so that astronomers will have reliable data.
Left: One of the first ALMA antennas at the OSF (Operations Support Facility), in the Verification phase before being taken to the Chajnantor plateau. Credit: ALMA (ESO / NAOJ / NRAO). R. Bennett (ALMA)
ALMA’s revolutionary antennas
ALMA’s superconducting receivers
The receivers in each of ALMA’s antennas will be chilled to within a few degrees of absolute zero, the lowest possible temperature (at which all molecular and atomic motion is at a minimum). These receivers are the finest ever made. They feature unprecedented bandwidth and noise levels that approach the lowest theoretically possible. The completed ALMA receiver system will be the largest assembly of superconducting electronics in the world.
Left: An ALMA “front end” awaits receiver cartridges at NRAO’s ALMA Front-End Integration Center in Charlottesville, Virginia.
Just as the inside of a camera must be dark, so a radio receiver that listens to incredibly faint signals coming from space must be “quiet”. One of the best techniques for suppressing receiver noise is to make the receivers very, very cold.
ALMA’s incredible imaging resolution
The longer the wavelength of the light, the fuzzier an image a telescope produces. The only way to get a really sharp picture from long-wavelength light is to make a really big telescope. To see with merely the sharpness that an unaided human eye enjoys in visible light, a millimeter-wavelength telescope has to be some 500 times wider than a human eye. ALMA’s 7- and 12-meter antenna dishes individually can thus see a bit more sharply than a human eye can. The entire ALMA array, however, will be able to resolve details as much as ten times better than the Hubble Space Telescope. By mathematically combining the signals from antennas spread over as much as 16,000 meters, we can, in effect, create the resolving power of a single 16-kilometer-wide telescope!
Left: The Horsehead Nebula in Orion, a dusty star-forming cloud, as seen in visible and submillimeter light. The submillimeter image, captured with a large, single-dish telescope, shows regions of possible star formation activity that are obscured in visible wavelengths by dust. ALMA will see such hidden details with a sharpness that exceeds the ground-based optical image here. Credit for visible-light image: ESO. Credit for submillimeter-light image: Joint Astronomy Centre
Once the effects of atmospheric turbulence are taken care of, a telescope’s ability to see fine details depends on only two things: The color (wavelength) of the light and the diameter of the telescope.
ALMA Fifty four 12-meter dishes and twelve 7-meter dishes
VLT Four 8.2-meter mirrors
HUBBLE One 2.4-meter mirror
The Light-Gathering Power of ALMA’s Antennas
Cool objects in space give off invisible light below the red end of the spectrum, and they give off a lot less light than hot objects such as stars emit. Detecting the faint, but important, whispers of light coming from places where stars and planets are forming requires instruments of stupendous light-gathering power.
When the electric voltage flowing through an incandescent lamp is reduced using a dimmer, the color of the light shifts more and more to the red and the intensity of the light decreases.
Left: ALMA’s light-gathering surface area compared to that of several visible-light observatories.
Just one of ALMA’s fifty-four 12-meter antennas is thus larger than the biggest visible-light telescope on Earth. (ALMA will also have twelve 7-meter antennas.)
The ALMA Antenna Transporters
In some astronomical observations, viewing the largest area of the sky possible is the highest priority. In others, capturing the finest details is most important.
This is done by moving the antennas. When they’re packed close together, ALMA is at its most sensitive to the large-scale features. When they’re spread far apart, ALMA can see with the highest resolution. Picking up a 100-ton antenna, moving it a few miles, and putting it down within a fraction of a millimeter of the intended position is no easy feat. The 140-ton ALMA Antenna Transporters – there are two, named Otto and Lore – are customdesigned “monster trucks” made for just this purpose. Their on-board power generators keep an antenna’s cryogenic systems running while it’s being moved. The Transporters will also bring antennas down to a lower altitude servicing facility for repairs, maintenance, and upgrades.
Left: Move of an ALMA antenna with a Transporter. Credit: ALMA (ESO / NAOJ / NRAO), W. Garnier (ALMA) Above: Artist’s rendering of typical transporter activity. Credit: ALMA (ESO / NAOJ / NRAO)
ALMA can “zoom” between these extremes, trading sensitivity to large-scale features for resolution, and vice-versa.
The ALMA Correlator
Our eyes can extract amazing information from the light that passes through them, mapping the distribution of light across the field of view. We call such a map an image.
It would take a hundred and fifty thousand personal computers to carry out the task. Do the math and you’ll discover why – for a lot less money – we decided to create the ALMA Correlator, the most powerful calculating machine known to the civilian world. Would you like to see it? And meet the people who created it?
Above: The ALMA Array Operations Site (AOS) Technical Building will house the ALMA Correlator. It is the second highest steel-frame building in the world. Credit: ALMA (ESO / NAOJ / NRAO), E. Donoso (NRAO) Left: A portion of the second quadrant of the ALMA Correlator undergoing tests at NRAO’s Technology Center.
To make images from millimeter-wavelength light gathered by multiple antennas (as a lens does effortlessly to visible light), we need absolutely colossal computing power. The signals coming from each pair of antennas – there are 1,225 pairs in just the extended array – must be mathematically compared billions of times every second.
The ALMA Sky
For four centuries telescopes of every kind have been treating us to views of the universe that intrigue, astound, and humble.
Left: This photo shows a three colour composite of the well-known Crab Nebula (also known as Messier 1). It is the remnant of a supernova explosion at a distance of about 6,000 light-years. Credit: ESO
With ALMA, the eerie luminance of the hidden universe of the very cold will snap into focus. We will behold with vivid clarity what no eye has yet seen.
“Nearby” galaxies seen by ALMA (simulated)
Distant/Early galaxies seen by ALMA (simulated)
Credit: W.-H. Wang (NRAO), L. L. Cowie (IfA, U. H., Honolulu), A.J. Barger (U.W.-Madison) “Nearby” galaxies seen by Hubble
Distant/Early galaxies seen by Hubble
Credit: K. Lanzetta, K. Moore, A Fernandez-Soto, A. Yahil (SUNY). © 1977 Kenneth M. Lanzetta
A distant galaxy seen (or not) in wavelengths of light ranging from visible through radio. The fifth picture shows submillimter light, in which the galaxy shines brighly. Credit: W.-H. Wang (NRAO)
ALMA reveals the earliest galaxies
As light from the Big Bang faded, the early universe grew profoundly dark. There were no stars, only the gas – mostly hydrogen, a little helium, traces of lithium and beryllium – from which the first stars would eventually form. No one knows exactly how long the “dark ages” lasted, but sometime during the first few hundred million years the first stars condensed from that gas and began to shine.
Even our most powerful telescopes cannot detect the light from individual firstgeneration stars. Upcoming space observatories will technically be able to register the much greater light from such a star as it explodes, but the chances of doing so – even once – over the lifespan of a space observatory are slim. It is, ironically, in the most humble stuff of the universe that our best hope of detecting the era of the first stars may lie. Among the material expelled into space as those stars exploded was dust, formed from the thermonuclear fusion of lighter elements inside the star. Dust’s first appearance is the “smoking gun” evidence that first stars have lived. ALMA is designed to detect dust in the early universe. Peering deep into space – remember, the farther we look, the further back in time we see -- ALMA will detect the glow of warm dust in galaxies farther away, and thus earlier in time, than any we can detect in the deepest visible- and infrared-light photography. Further information about the early universe may come though spectroscopic observations of carbon isotopes, since the mix of isotopes produced in stars over cosmic history is expected to evolve.
Left background: A portion of the Hubble Ultra Deep Field. Credit: NASA, ESA, S. Beckwith (STScI) and the HUDF Team
Far & Long Ago
According to theory, these first stars were incredibly massive and luminous, much more so than is possible for stars forming today. They lived for only a million years before spectacularly exploding, spewing into space chemical elements forged deep in their cores.
A simulated ALMA observation of light emitted by methyl cyanide molecules in a massive, rotating protostellar disk. Credit: Mark Krumholtz, University of California Santa Cruz.
A simulated ALMA observation of the dusty debris disk around the star Vega. The gravity of a massive planet appears to be gathering dust into clumps, the rotation of which ALMA will be able to observe. Credit: R. Reid (NRAO); model by M. Wyatt (Cambridge Univ.)
Simulated ALMA observations of disk-embedded, Jupiter-size planets at distances from Earth of 50 and 100 parsecs (about 160 and 325 light-years, respectively). Credit: Sebastian Wolf, Christian-Albrechts-Universit채t zu Kiel.
ALMA unveils the formation of stars and planets Stars shine for millions and billions of years, but their formation, taking mere thousands of years, remains literally shrouded in mystery. Visible-light telescopes cannot see into the dusty concentrations of gas from which stars are born. Infrared telescopes reveal newly-born stars before they fully emerge from their dusty cocoons, but cannot see the actual processes of a star’s pre-ignition development. We know that immense clouds collapse under gravity to make stars. But how do they fragment into smaller clouds to become a mix of small and large stars? How does gravity overcome the turbulence, outflows, and magnetic forces that resist a cloud’s collapse? Even harder, how do the stars that are destined to become very massive ones keep accumulating gas once they’ve lit up? Why don’t winds flowing out from those stars stop further growth?
According to our best current understanding, planets form around a new star by condensing within a disk of molecular gas and dust that is embedded within a much larger molecular cloud. The condensations grow to become giant planets, getting warmer, clearing paths in the disk, and possibly warping the disk. Eventually, the gas that remains in the disk is cleared out, leaving behind planets and a disk of dust and debris. ALMA will study all phases of planet formation. It will probe protoplanetary disks in high resolution. It may be able to detect the light from growing, warming protoplanetary cores, and to directly detect giant planets clearing paths in disks. ALMA will be able to find even more planets by measuring the exquisitely small effects they have on the motion of the stars they orbit (perhaps enabling us to measure the mass of some planets that have already been discovered), and to examine dusty debris disks that remain around stars once the gas has been removed. Left: Colour-composite image of the Carina Nebula, revealing exquisite details in the stars and dust of the region. Credit: ESO
ALMA will look deep into star-forming clouds, detect the faint light emitted by infalling matter that is just starting to heat up, and actually map the motion of that matter.
ALMA investigates dust and molecules in space
On the microscopic landscapes of dust grains in space reside chemical factories of mind-boggling complexity. Chemical elements link up to become molecules. This process continues and diversifies as molecules are liberated from the dust by warming, becoming gaseous in space. Molecules created in these ways may seed young planets with the building blocks of life.
ALMA will have an unprecedented ability to discover and measure the presence of molecules and their distribution in interesting structures in space. We will learn about the chemistry of space, irreproducible in laboratories on Earth, and the evolving conditions that drive it.
Formamide Carbon Monoxide
Acetic Acid Methane Formaldehyde
Left: This image of the large spiral galaxy NGC 1232, in the constellation Eridanus at about 100 million light-years, is based on three exposures in ultra-violet, blue and red light. Credit: ESO
If chemical elements, whose celestial abundances are studied with visible-light telescopes, are like letters of the alphabet, molecules are like words formed from the letters. Theyâ€™re more diverse, complex, and interesting. Such molecules do not survive well the temperatures (thousands of degrees) to which visible-light telescopes are tuned; it takes radio telescope technology to observe most of them.
ALMA studies our nearest star
Most telescopes, wisely, are never pointed at the Sun. But ALMA can safely study our star; its antenna surfaces diffuse the visible light and heat while focusing the millimeter-wavelength light. ALMA will investigate the great eruptions (flares) that occur on the Sun and the high-speed particles that are emitted. It will study the structure and evolution of solar prominences and filaments, strands of 6,000 degree gas suspended in the Sunâ€™s 3 million degree atmosphere (corona).
Left: Possibly the most powerful solar flare ever witnessed, on November 4, 2003, seen in ultraviolet light by the SOHO satellite. Artifacts in the image are caused by detector saturation. Courtesy SOHO (ESA & NASA)
That the Sun has such a hot atmosphere is a mystery. ALMA will probe the part of the Sunâ€™s atmosphere just below where the temperature skyrockets. It may help us understand areas of the solar atmosphere inaccessible to study in any other way.
ALMA explores the worlds that circle our Sun
Our solar system is the one tiny part of the universe that we can visit via robotic probes. But there are thousands of planets, moons, asteroids, and comets, and money for only a few probes at a time. A big role for earth-based observatories remains. ALMA will image planets and measure their winds. It will analyze molecules emitted by comets and asteroids even when they’re at their most interesting and active, passing near the sun – a time when other telescopes must turn their gaze away.
ALMA will discover thousands of new Kuiper Belt objects (the class of worlds to which we now know Pluto belongs), observing the light that they emit, not their reflected sunlight. This will let us calculate their true sizes.
Above left: Artist impression of the Kuiper Belt. Credit: artwork © Don Dixon/cosmographica.com. Above right: Water jets erupting from Saturn’s moon Enceladus, as seen by NASA’s Cassini Orbiter. Credit: NASA/JPL/Space Science Institute. Left: Comet C/2001 Q4 (NEAT) photographed at Kitt Peak National Observatory on May 7, 2004. Credit: T. A. Rector (University of Alaska Anchorage), Z. Levay & L. Frattare (Space Telescope Science Institute) and WIYN/NOAO/AURA/NSF
Studying comet composition will give us new insights into the make-up of the early solar system, as will observations of molecules being sprayed into space by geysers on worlds such as Saturn’s moon Enceladus.
ALMAâ€™s greatest discoveries, the ones we cannot foresee
Light ceaselessly rains down on us from the sky. Whenever we advance our abilities to capture and analyze this light, the universe reveals new secrets.
Left: The stars and dust of the Milky Way and the Large Magellanic Cloud fill the night sky above the ALMA site. Credit: ESO
As with the great telescopes that have gone before it, ALMA will enable us to see aspects of the universe whose existence we didnâ€™t even suspect.
The people, the skills, the countries building ALMA
ALMA is a partnership between the scientific communities of Europe, North America and East Asia in cooperation with Chile. Each region contributes antennas, scientific and design expertise, and receiver technology. Specific contributions include: • 50 12-meter and 16 7-meter antennas • Correlators for the extended ALMA array and the Atacama Compact Array (ACA) • Receiver cartridges • The Photonic Local Oscillator • Digital electronics that transmit output signals to the correlator • Front-End Integration Centers • The Array Operation Site (AOS) Technical Building (second highest steel building in the world)
• A lot of smart software
So Top left: Panoramic view of the Assembly, Integration and Verification area at ALMA’s Operations Support Facility (OSF). Credit: ALMA (ESO / NAOJ / NRAO). Bottom left: Workers building an ALMA antenna foundation. Credit: ALMA (ESO / NAOJ / NRAO)
• The Operations Support Facility (OSF) Technical Building (housing the Control Room and administration offices)
ALMA’s public data archive
Scientists from around the world will compete for ALMA observing time (Chilean astronomers will have a 10% of this time, while the rest is divided among ALMA’s partners). For the first 12 months after an observation, the astronomers who proposed the observation will have exclusive access to their data. But after that, the data will become public, a vast library growing at a rate of 800 gigabytes per day. For the first few years of ALMA operations, new observational data will be the primary source of new discoveries and insights. Eventually, the data archive will take on a life of its own, becoming a treasure of information waiting to be “mined” in ways not yet envisioned.
7.0 6.0 5.0 4.0
1.0 0 2004
Year Left: Data servers at NRAO headquarters in Charlottesville, Virginia. Above: The digital data archive for NRAO’s Very Large Array (VLA) went online in 2004. Within three years the amount of data being retrieved from the archive every week exceeded the amount of new data flowing in. Credit: NRAO
VLA Archive Data Transfer (TBytes)
ALMA Infoglut and tools to handle it
ALMA will possess 100 times the sensitivity, 100 times the imaging resolution, and 100 times the spectral agility of its immediate millimeter/submillimeterwavelength predecessors. A leap of that magnitude has never before been accomplished in astronomy. Astronomers, accustomed to struggling to obtain data at the fringe of what can be observed, will suddenly find themselves drowning in it. Particularly daunting will be the thousands upon thousands of spectral lines that will emerge from what, in previous-generation instruments, was simply background noise.
So Left: Screen shots from a variety of software applications being developed to help simulate and analyze ALMA data and performance. Credit: NRAO
ALMAâ€™s partners are hard at work developing new tools to help astronomers sift through the embarrassment of riches that awaits them in a few short years.
ALMAâ€™s value to all of us
Astronomy is unique among the sciences in its power to capture the imagination. As the major new ground-based observatory for the coming decades, ALMA will have an impact broader than just that of the particular discoveries it makes, inspiring budding scientists and science enthusiasts everywhere with the message that great frontiers await exploration, that the means are at hand, and that a career in science is one with a future.
So Left: Children from the city of Calama enjoying ALMAâ€™s interactive scale model. Credit: ALMA (ESO / NAOJ / NRAO). R. Bennett (ALMA)
ALMA will contribute profoundly to the satisfaction of curiosity, not just that of the professional researcher, but of the child who looks into a sky full of stars and wonders what they are.
Array Operation Site (AOS) - 5,000 m
Vicu単as in the ALMA site
Archaeological site museum in the ALMA site
We’d like to make it easy for you to tell ALMA’s many stories The Atacama Large Millimeter/submillimeter Array (ALMA) is a revolutionary instrument in its scientific concept, its engineering design and its organization as a global scientific endeavour and we would be delighted to help you tell your audiences about us. We can assist with:
• Scientist and engineer interviews, on site or via telephone. • Photography/videography access to the ALMA site in Chile, accompanied by our on-site representatives and colleagues.
Please contact us: William Garnier ALMA Education and Public Outreach Officer (562) 467 6100 - 467 6119 / firstname.lastname@example.org
• High resolution photography and HD video footage.
Chajnantor plateau at sunrise. Credit: ALMA (ESO / NAOJ / NRAO)
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
ALMAâ€™s Operations Support Facility building at an altitude of 2,900 meters. Credit: ALMA (ESO / NAOJ / NRAO)
Front cover: Artistâ€™s rendering of the completed ALMA array. Credit: ALMA (ESO / NAOJ / NRAO)
Published on Sep 27, 2012