Very Large Telescope Reveals Low-Mass Bodies in Orion Nebula

The HAWK-I IR instrument on the European Southern Observatory’s (ESO) Very Large Telescope (VLT) has been used to produce the deepest and most comprehensive view of the Orion Nebula to date. The striking image reveals an abundance of faint brown dwarfs and isolated planetary-mass objects, and the presence of such low-mass bodies provides insight into the history of star formation within the nebula itself.

An image of the Orion Nebula star-formation region obtained from multiple exposures using the HAWK-I IR camera on ESO's Very Large Telescope in Chile. This is the deepest view ever of this region and reveals more very faint planetary-mass objects than expected. Courtesy of ESO/H. Drass, et al.

The Orion Nebula spans about 24 light-years within the constellation of Orion, and is visible from Earth with the naked eye as a fuzzy patch in Orion's sword. Its relative proximity makes it an ideal testbed to better understand the process and history of star formation, and to determine how many stars of different masses form. Some nebulae, like Orion, are strongly illuminated by UV radiation from the many hot stars born within them, such that the gas is ionized and glows brightly.

Researchers from Ruhr-Universität Bochum and Max-Planck Institut für Astronomie in Germany, and Pontificia Universidad Católica de Chile and Universidad de Valparaíso in Chile, who produced and analyzed the image, said that understanding how many low-mass objects are found in the Orion Nebula is very important to constrain current theories of star formation.

The ESO Very Large Telescope (VLT) during observations. In this picture, taken from the VLT platform looking north-northwest at twilight, the four 8.2-m unit telescopes (UTs) are visible. From left to right are Antu, Kueyen, Melipal and Yepun, the Mapuche names for the VLT's giant telescopes. In front of the UTs are the four 1.8-m auxiliary telescopes (ATs), entirely dedicated to interferometry. The configuration of the ATs can be changed by moving them across the platform between 30 different observing positions. One of these positions is visible in the foreground, covered by a hexagonal pad. A reddish laser beam is being launched from UT4 (Yepun) to create an artificial star at an altitude of 90 km in the Earth´s mesosphere. This laser guide star is part of the adaptive optics system, which allows astronomers to remove the effects of atmospheric turbulence, producing images almost as sharp as if the telescope were in space. The bluish compact group of stars visible to the right of the laser beam is the Pleiades open cluster.

The image helped elucidate the way the formation of such low-mass objects depends on their environment, and the researchers said the Orion Nebula may be forming proportionally far more low-mass objects than closer and less active star formation regions.

These observations also hint that the number of planet-sized objects might be far greater than previously thought, and for which effective observation technology does not yet exist. ESO's European Extremely Large Telescope (E-ELT), scheduled to begin operations in 2024, is designed to observe these objects.