"Galaxy Blue" by Souricette-du-13 / CC BY-SA 4.0

These dusty young stars are changing the rules of planet-building

Dec 5, 2018

By Rebecca Boyle

Some 100,000 years ago, when Neanderthals still occupied the caves of southern Europe, a star was born. It appeared when a ball of gas collapsed and ignited within a stellar factory known as the Taurus Molecular Cloud. Then, leftover material began to cool and coalesce around it, forming dust grains and a hazy envelope of gas.

In September 2014, some of the light from that hot young star and its surroundings landed inside 66 silvery parabolas perched on a plateau in Chile’s Atacama desert — the driest on Earth. The photons had taken 450 years to make the journey. Astronomers were waiting. They were conducting a test of the Atacama Large Millimeter/submillimeter Array (ALMA), which features radio antennas separated by distances of up to 15 kilometres. With such long spans between them, the antennas work as a high-resolution receiver that can discern cool objects less than a millimetre across.

When the telescope team trained ALMA on the young star, named HL Tauri, they expected to see a bright smear of dust and gas. Instead, when ALMA’s supercomputer stitched together those photons, the image resolved into a disk with a well-defined ring structure, with gaps seemingly etched by small, infant planets orbiting a central star. It looked like a furry, orange Saturn1. It looked like nothing astronomers had ever seen.

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