November 14, 2012

New star cluster identified in front of Orion nebula

Orion Nebula, the most studied star formation region in space, is actually a complicated mix of these two star clusters, a new study has revealed.

Using images from the 340 megapixel MegaCam camera on the Canada-France-Hawaii Telescope (CFHT) from the summit of Mauna Kea, astronomers identified the massive cluster of young stars NGC 1980 to be a clearly separate entity from the main cluster i.e. Orion Nebula.
A technique relying on the combination of optical, infrared, and mid-infrared data ensures astronomers are sampling only stars located in the foreground of the Orion nebula. This technique also led them to the discovery of a nearby small star cluster, baptized L1641W.

Although astronomers knew of the presence of a foreground stellar population since the 1960s, the new CFHT observations revealed that this population is more massive than first thought, and it is not uniformly distributed, clustering around the star iota Ori at the southern tip of Orion's sword.

The importance of this discovery is two-fold: first, the cluster identified as a separate entity is only a slightly older sibling of the Trapezium cluster at the heart of the Orion nebula, and second, what astronomers have been calling the Orion Nebula Cluster (ONC) is actually a complicated mix of these two clusters.

Herve Bouy, from the European Space Astronomy Centre in Madrid, one of the two authors of this work, explains that “we need refine what we thought were the most robust star and cluster formation observables.”

He points out the need for a long follow-up work on Orion where “we must untangle these two mixed populations, star by star, if we are to understand the region, and star formation in clusters, and even the early stages of planet formation.”

“For me the most intriguing part is that the older sibling, the iota Ori cluster, is so close to the younger cluster still forming stars inside the Orion nebula” said Joao Alves for the University of Vienna.

“It is hard to see how these new observations fit into any existing theoretical model of cluster formation, and that is exciting because it suggests we might be missing something fundamental. Clusters are very likely the favourite mode of star formation in the Universe, but we are still far from understanding why that is exactly,” Alves added.

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