World’s most powerful telescope turns to the stars

The Alma sub-millimetre array, a huge telescope made of dishes spread over miles of Andean desert, has captured its first extraordinary images, shedding new light on the birth of stars.

Five thousand metres above sea level, on the desert wasteland of Chile's Chajnantor Plateau, the world's most powerful astronomical instrument has swung into action. An array of 22 huge reflective dishes, representing the cutting edge of telescope technology, turns ponderously through the thin, freezing mountain air, probing the secrets of the most distant stars.

Their first target: a pair of galaxies called the 'Antennae', 13.5 billion light years distant. The few faint photons being focused in the Alma dishes are the product of an ancient galactic collision, which took place a mere 500 million years after the universe was born but is only now becoming visible on Earth.

The Antennae galaxies – each containing billions of raging, primitive stars – got caught in each other's gravity wells, spiralling together in a slow motion dance of death.

This apocalyptic moment can be seen with existing telescopes – but the snapshots that conventional machines take are missing something crucial. Like a letter in a spy movie, the Antennae galaxies conceal a secret, visible only to those who can read between the lines.

This is where the Alma array comes in. Most telescopes can 'see' only certain wavelengths of radiation: the relatively short lengths we call the 'visible light spectrum'. Some specialised telescopes can work with long wavelengths, called radio waves. Ultra-high tech dishes make Alma one of a handful of telescopes to be able to detect a narrow band of wavelengths in the middle, called 'sub-millimetre'.

Images from ordinary telescopes, using the visible light spectrum, show the Antennae galaxies surrounded by swirling black clouds of dust. If you look at the galaxies in the sub-millimetre wavelengths, however, these dark clouds can be seen giving off a mysterious glow, like a message written in invisible ink that suddenly emerges when you see it under UV light.

What does the glow mean? It is the faint dim light given off by the birth of a new generation of stars – stars that may, by now, be stable life-giving suns, similar to our own.

Creation and destruction

The Alma array means that, for the first time, we can actually see this stellar creation happening. It is not, however, a new discovery. Scientists had already deduced that stars were being born within the galactic gas clouds, and some will say that although the pictures are pretty, they do little to advance the frontiers of human knowledge.

But to actually see such a monumental moment of creation and destruction taking place has a beauty and importance all of its own, others will reply. The Alma telescope gives us a new opportunity to marvel at the grandeur, the scale and the terrifying power of the universe.

You Decide

  1. Is the universe beautiful, terrifying – or both?
  2. The Alma array cost over €1 billion. Worth the money?


  1. Imagine you had €1 billion to spend on a science project of your choice. What would you choose? Write a proposal for your favourite possibility?
  2. Sub-millimetre astronomy relies on the differing properties of different wavelengths of light. Construct a chart showing the properties and uses of the spectrum of wavelengths from gamma rays to radio waves. Explain, if you can, why the different wavelengths behave the way they do.

Some People Say...

“Looking at whole galaxies shows us that humans are insignificant.”

What do you think?

Q & A

Why would you build a telescope on a freezing cold plateau in Chile?
Partly because it's high and remote. There is no light pollution and there is less atmosphere to block incoming radiation. Mainly, though, it's because the plateau is incredibly dry.
So what?
Water absorbs sub-millimetre wavelength radiation. Any rainfall would render the telescope effectively blind.
And why does the telescope look like a series of satellite dishes?
The dishes collect photons coming in from space over a very wide area. The information from all the dishes is then processed by a central computer, and put together to make a final image.

Word Watch

13.5 billion light years
A light year is the distance a beam of light can travel in a year. That means that when we see something 13.5 billion light years away the light we are perceiving was emitted 13.5 billion years ago. The universe itself is only around 14 billion years old.
A single unit of light. A photon is an elementary particle with zero mass.
Full name: the Atacama Large Millimetre/Sub-millimetre Array
Primitive stars
Stars in the early universe were short-lived, fast burning giants, which produced all the elementary building blocks for planets – and life – in their white hot cores.
Light, extraordinarily, behaves as both a particle (photon) and a wave. The distance between neighbouring wave crests is the wavelength, which can vary from billionths of a millimetre to thousands of metres.


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