Update: November 2014. Astronomers have captured the best image ever of planet formation around an infant star, using the Atacama Large Millimeter/submillimeter Array’s (ALMA) new high-resolution capabilities. The image reveals in astonishing detail the planet-forming disk surrounding HL Tau, a Sun-like star located approximately 450 light-years from Earth in the constellation Taurus.
HL Tau is hidden in visible light behind a massive envelope of dust and gas. Since ALMA observes at much longer wavelengths, it is able to peer through the intervening dust to study the processes right at the core of this cloud.
Stars form within clouds of gas and dust that collapse under gravity. Over time, the surrounding dust particles stick together, growing into sand, pebbles, and larger-size rocks, which eventually settle into a thin protoplanetary disk where asteroids, comets, and planets form. Once these planetary bodies acquire enough mass, they dramatically reshape the structure of their natal disk, fashioning rings and gaps as the planets sweep their orbits clear of debris and shepherd dust and gas into tighter and more confined zones.
The multiple concentric rings separated by clearly defined gaps around HL Tau suggest that planet formation is already well underway around this young star (no more than a million years old). The new ALMA image reveals these striking features in exquisite detail, providing the clearest picture to date of planet formation. Images with this level of detail were previously only seen in computer models and artist concepts. ALMA has now provided direct proof that nature and theory are very much in agreement.