April 20, 2009
Astronomers, using the United Kingdom Infrared Telescope (UKIRT) in Hawaii, the IRAM Millimeter-wave Telescope in Spain, and the Spitzer Space Telescope in orbit above Earth, have completed the most wide-ranging census ever produced of dynamical star formation in and around the well-known Orion Nebula (M42). They have found this stellar nursery to be a lively and somewhat overcrowded place, with young stars emitting gas jets in all directions and creating quite a chaotic picture. There is much more going on in Orion than previously thought.
The research team comprises more than a dozen astronomers from the United States, the United Kingdom, and a number of other European countries. A number of them are in Hertfordshire in the United Kingdom this week to share their discoveries with colleagues at this year's annual National Astronomy Meeting of the United Kingdom (NAM 2009).
Take a look at the constellation Orion at night. With the naked eye, you see only the brightest stars, such as Betelgeuse (Alpha [α] Orionis) and Rigel (Beta [β] Orionis) at the shoulder and knee of the constellation, or perhaps the Orion Nebula as a vaguely fuzzy patch around the sword. What your eye does not see is an enormous cloud of molecules and dust particles that hides a vast region where young stars are being born. In the sky, the region — known to astronomers as the Orion Molecular Cloud — is more than 20 times the angular size of the Full Moon, spanning from far above the Hunter's head to far below his feet. It is one of the most intense regions of star formation in the local Milky Way and has been the subject of many small-scale studies over the years. However, the current work is the first to present such a complete study of the young stars, the cloud of gas and dust from which they are being born, and the spectacular supersonic jets of hydrogen molecules being launched from the poles of each star.
Most of the "action" is hidden from view in visible light because the molecular cloud is thick and opaque. Only the Orion Nebula, which is really just a blister on the surface of the cloud, gives an indication of what is really happening within. To see through the cloud, we need to observe at wavelengths beyond the reach of the human eye. The longer (or "redder") the wavelength, the better. Thus, the team has used UKIRT, Spitzer — which works at even longer "mid-infrared" wavelengths — and the IRAM radio telescope, which operates beyond the infrared at short radio wavelengths.
The key to the success of this project was the combination of data from all three facilities. Inspired by the richness of his images from UKIRT, Chris Davis contacted colleagues in Europe and on the United States mainland. Tom Megeath, an astronomer from the University of Toledo in Ohio, provided a catalogue of the positions of the very youngest stars — sources revealed only recently by Spitzer. Thomas Stanke, a researcher based at the European Southern Observatory in Garching, Germany, then provided extensive IRAM maps of the molecular gas and dust across the Orion cloud. Dirk Froebrich, a lecturer at the University of Kent in the United Kingdom, later used archival images from the Calar Alto Observatory in Spain (data acquired by Stanke some 10 years ago) to measure the speeds and directions of a large number of jets by comparing them with their positions in the new images. Armed with these data, Davis was able to match the jets up to the young stars that drive them, as well as to density peaks within the cloud — the natal cores from which each star is being created.
"Regions like this are usually referred to as stellar nurseries," Davis said, "but we have shown that this one is not being well run: It is chaotic and seriously overcrowded. Using UKIRT's wide field camera (WFCAM), we now know of more than 110 individual jets from this one region of the Milky Way. Each jet is traveling at tens or even hundreds of miles per second; the jets extend across many trillions of miles of interstellar space. Even so, we have been able to pinpoint the young stars that drive most of them."
Froebrich mentioned that "measuring the speeds and directions of the jets is essential to pinpoint the driving sources, especially in such crowded regions as M42 in Orion."
Megeath added: "With such a large number of young stars, we can study the 'demographics' of star birth. This study will give us an idea of how long it takes baby stars to bulk up by pulling in gas from the surrounding cloud, what ultimately stops a star from growing bigger, and how a star's birth is influenced by other stars in the stellar nursery."
"Star-formation research is fundamental to our understanding of how our own Sun, and the planets that orbit it, were created," Stanke noted. "Many of the stars currently being born in Orion will evolve to be just like the Sun. Some may even have earthlike planets associated with them."
Andy Adamson, Associate Director at the UKIRT, said: "This spectacular dataset demonstrates the power of survey telescopes like UKIRT. With online access to data from other telescopes around the world, and the ease with which one can communicate with collaborators across the globe, massive projects like the Orion study are very much the future of astronomy."
Adamson, along with Gary Davis, director of UKIRT, presented this and other UKIRT science results at the European Week of Astronomy and Space Science (NAM 2009) at the University of Hertfordshire.