The Atacama Large Millimetre Array

This radio telescope, known as the Atacama Large Millimetre Array (ALMA), will be a front-line astronomical tool for decades to come.


On March 13, a major astronomical facility was officially opened. This radio telescope, known as the Atacama Large Millimetre Array (ALMA), will be a front-line astronomical tool for decades to come. Located on the high and very arid Atacama Plateau in Chile, it is an international project with Canada as a major participant.

This instrument, which consists of 66 12-m diameter dishes, is designed to measure and map the millimetre wavelength emissions from space. These are short radio waves that are close to the infrared part of the spectrum.  To deal with these short wavelengths, the antenna surfaces have to be accurate to within a fraction of the thickness of a human hair, in all weathers. Unlike the longer radio wavelengths, millimetre waves are strongly affected by the atmosphere, particularly water vapour, hence ALMA being located in a high, dry place.

There are some other instruments in the world capable of observing in this technically difficult part of the radio spectrum, but none even come close to the sensitivity and imaging power of ALMA. Even in these early days, this radio telescope is showing us things we have never been able to see before.

Millimetre waves are produced in two main ways. Any material having a temperate of a few degrees above absolute zero (-273C) emits them, so we can use this radio telescope to image clouds of gas and dust, such as those we see in our galaxy and others. Of particular interest are the collapsing and rotating clouds that are in the process of forming new stars and planets. Just as interesting are the radio signatures of the chemicals making up those clouds. They have signatures at millimetre wavelengths, so using instruments such as ALMA, we can detect them and measure their amounts, and even how they are moving. ALMA can also map where the different chemicals are located in the clouds and how and why they are reacting with one another.

Although we are curious about “cosmic chemistry” for its own sake, we are also interested because we want to know how the recipe for making living creatures came about. When our universe first cooled enough for the first elements to form, those primordial elements were hydrogen, helium and lithium. Stars formed from this mixture, and obtained energy during their lives by turning these elements into others, such as oxygen, phosphorus, nitrogen, sulphur, and also metals such as iron and nickel. Then, when those first, extra-bright stars exploded at the ends of their lives, they made gold, silver, uranium, lead, platinum and the rest of the elements we know today.  This “nuclear waste” was added to the cosmic clouds, and over millions of years, chemistry got to work, making water, ammonia, ethanol, methanol, formaldehyde and countless other chemicals. Many of these are key ingredients of life as we know it.

One intriguing early result from ALMA, thanks to its unprecedented sensitivity, is that the first stars formed in the young universe even earlier than we thought, between one and two billion years after the Big Bang, which took place 13.7 billion years ago.

Jupiter dominates the southwestern sky during the night. Saturn rises around 10 p.m.  The Moon will be at last quarter on the 2nd and new on the 10th.

Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astro-physical Observatory, Penticton.


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