World (ESO) – Stellar explosions are most often associated with supernovae, the spectacular deaths of stars. But new ALMA observations provide insights into explosions at the other end of the stellar life cycle, star birth. Astronomers captured these dramatic images as they explored the firework-like debris from the birth of a group of massive stars, demonstrating that star formation can be a violent and explosive process too.
1350 light years away, in the constellation of Orion (the Hunter), lies a dense and active star formation factory called the Orion Molecular Cloud 1 (OMC-1), part of the same complex as the famous Orion Nebula. Stars are born when a cloud of gas hundreds of times more massive than our Sun begins to collapse under its own gravity. In the densest regions, protostars ignite and begin to drift about randomly. Over time, some stars begin to fall toward a common centre of gravity, which is usually dominated by a particularly large protostar — and if the stars have a close encounter before they can escape their stellar nursery, violent interactions can occur.
About 100 000 years ago, several protostars started to form deep within the OMC-1. Gravity began to pull them together with ever-increasing speed, until 500 years ago two of them finally clashed. Astronomers are not sure whether they merely grazed each other or collided head-on, but either way it triggered a powerful eruption that launched other nearby protostars and hundreds of colossal streamers of gas and dust out into interstellar space at over 150 kilometres per second. This cataclysmic interaction released as much energy as our Sun emits in 10 million years.
Fast forward 500 years, and a team of astronomers led by John Bally (University of Colorado, USA) has used the Atacama Large Millimeter/submillimeter Array (ALMA) to peer into the heart of this cloud. There they found the flung-out debris from the explosive birth of this clump of massive stars, looking like a cosmic version of fireworks with giant streamers rocketing off in all directions.
Such explosions are expected to be relatively short-lived, the remnants like those seen by ALMA lasting only centuries. But although they are fleeting, such protostellar explosions may be relatively common. By destroying their parent cloud, these events might also help to regulate the pace of star formation in such giant molecular clouds.
Hints of the explosive nature of the debris in OMC-1 were first revealed by the Submillimeter Array in Hawaii in 2009. Bally and his team also observed this object in the near-infrared with the Gemini South telescope in Chile, revealing the remarkable structure of the streamers, which extend nearly a light-year from end to end.
The new ALMA images, however, showcase the explosive nature in high resolution, unveiling important details about the distribution and high-velocity motion of the carbon monoxide (CO) gas inside the streamers. This will help astronomers understand the underlying force of the blast, and what impact such events could have on star formation across the galaxy.
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
This report prepared by European Southern Observatory.