ALMA’s view of the dust within the cold interior of ‘The Brick’, an immense dense molecular cloud that may be forming a massive cluster of stars. This 3-mm continuum image covers 1.5 x 3 arcmins and improves remarkably our ability to resolve and measure the individual stellar embryos within this unique cloud. Obtained with only a fraction of ALMA’s full capabilities and taking a mere six hours of time, this breathtaking image is already changing our understanding of how immense clouds of dust and gas collapse to form star clusters.

By Jill Rathborne – CSIRO Astronomer

The Atacama Large Millimetre/submillimeter Array (ALMA) telescope is now officially open for business. Its inauguration, held mid-March 2013, marked an important transition for this groundbreaking project, from the construction phase to a fully fledged observatory. Representatives from the global scientific community, current and former ALMA personnel, as well as the members of local communities, all joined together to toast to its success.

Previously, in December 2012 the global scientific community had met in southern Chile to showcase and discuss the first results from ALMA’s ‘early science’ phase. While only utilising a limited number of antennas and a fraction of its full capabilities, the images provided by ALMA are already changing our view of the cool, dusty Universe. Results presented at this meeting were eagerly anticipated and the excitement surrounding ALMA’s full potential was high.

The team I led presented results at this meeting, having been one of the fortunate few teams to have accessed ALMA in its early science phase. Our observations obtained a large mosaic of the 3-mm line and continuum emission across a very cold, dense molecular cloud that sits close to the centre of our Galaxy. This extreme cloud, dubbed ‘The Brick’ because it is so cold and dense that it blocks background light, was identified as unique during surveys of the Galactic plane taken with CSIRO’s Mopra telescope.

The Brick has caught our attention as it may be a precursor to a very massive star cluster. While extreme star clusters exist in our Galaxy, very little is known about their formation. By looking into the cold interiors of clouds like The Brick with unprecedented detail, ALMA has the potential to reveal how the most massive stars and clusters in our Galaxy are formed. Where previous telescopes saw these stellar nurseries as big, amorphous blobs, ALMA has the ability to resolve and measure the individual stellar embryos. By counting how many stellar embryos there are within clouds like The Brick, measuring their masses, and determining how they are moving with respect to one another we can begin to test theories that describe how the most massive star clusters are formed.

The ALMA images of The Brick are spectacular and reveal a complicated web of gas and dust, in both emission and absorption. We are seeing, for the first time, the details of how massive clouds of gas and dust collapse. ALMA has ‘snapped into focus’ the small pockets of gas and dust that will eventually form the stars: we have found more than 50 of these stellar embryos within The Brick, each with masses close to 1,000 solar masses. The ALMA images contain so much information that it’s likely we’ll be analysing these data for years to come.

While it’s already producing game-changing results, ALMA is just warming up. Stay tuned for some very exciting results that are guaranteed to revolutionise our understanding of the cool Universe.

A short video on star formation and The Brick.