Searching for Orion’s protostars

This dramatic new image of cosmic clouds in the constellation Orion the Hunter reveals what seems to be a fiery ribbon in the sky. This orange glow represents faint light coming from grains of cold interstellar dust at wavelengths too long for human eyes to see. The European Southern Observatory-operated Atacama Pathfinder Experiment (APEX) in Chile observed it.

Clouds of gas and interstellar dust are the raw materials from which stars are made. But these tiny dust grains block our view of what lies within and behind the clouds — at least at visible wavelengths — making it difficult to observe the processes of star formation.

This is why astronomers need to use instruments that are able to see at other wavelengths of light. At submillimeter wavelengths, rather than blocking light, the dust grains shine due to their temperatures of a few tens of degrees above absolute zero. The APEX telescope with its submillimeter-wavelength camera LABOCA, located at an altitude of 16,400 feet (5,000 meters) above sea level on the Chajnantor Plateau in the Chilean Andes, is the ideal tool for this kind of observation.

This spectacular new picture shows just a part of a bigger complex called the Orion Molecular Cloud. A rich melting pot of bright nebulae, hot young stars, and cold dust clouds, this region is hundreds of light-years across and located about 1,350 light-years from Earth. The submillimeter-wavelength glow arising from the cold dust clouds is seen in orange in this image and is overlaid on a view of the region taken in the more familiar visible light.

The large bright cloud in the upper right of the image is the well-known Orion Nebula (M42). It is readily visible to the naked eye as the slightly fuzzy middle “star” in the sword of Orion. The Orion Nebula is the brightest part of a huge stellar nursery where new stars are being born, and it is the closest site of massive star formation to Earth.

The dust clouds form beautiful filaments, sheets, and bubbles as a result of processes, including gravitational collapse and the effects of stellar winds. These winds are streams of gas ejected from the atmospheres of stars, which are powerful enough to shape the surrounding clouds into the convoluted forms seen here.

Astronomers have used these and other data from APEX along with images from the European Space Agency’s Herschel Space Observatory to search the region of Orion for protostars — an early stage of star formation. They have so far been able to identify 15 objects that appeared much brighter at longer wavelengths than at shorter wavelengths. These newly discovered rare objects are probably among the youngest protostars ever found, bringing astronomers closer to witnessing the moment when a star begins to form.