Colorful outflows from young protostars in Orion the Hunter plunge into the thick dust of a molecular cloud in this new infrared image.
A small slice of the molecular cloud known as OMC-2 in Orion explodes to life in this new JWST image. Young protostars and their powerful outflows highlight a region chock full of cold gas and dust. Credit: ESA/Webb, NASA & CSA, T. Megeath (University of Toledo), M. Zamani (ESA/Webb); Acknowledgement: M. H. Özsaraç
Few sights thrill backyard observers as much as the Orion Nebula (M42). The brightest stellar nursery visible from mid-northern latitudes resolves into a complex web of luminous gas and dusty tendrils even through modest telescopes. And at its core, you’ll see the brilliant young stars of the Trapezium Cluster that provide the energy to set the nebula aglow.
Astronomers likewise study M42, looking for clues about how stars form. But not all of them focus on the glowing clouds that so enamor visual observers. The young stellar embryos known as protostars hide inside thick clouds of cold molecular gas and dust, and are still hundreds of thousands to millions of years from reaching the main sequence and official stardom. To make the observational challenge even worse, much of the action takes place slightly behind M42.
Piercing the murk
That’s where the James Webb Space Telescope (JWST) comes in. It sees infrared light, which largely penetrates cold gas and dust to reveal what lies inside. The telescope recently examined a tiny portion of the vast Orion A complex, which harbors several molecular clouds, bright nebulae, and young star clusters.
JWST’s target lies within the so-called Integral-Shaped Filament. At infrared and radio wavelengths, this region resembles an elongated letter S, so scientists named it after the similar-looking mathematical symbol for an integral. The Orion Nebula sits at the center of the filament. Just behind M42 dwells a chain of four cold molecular clouds called, appropriately, the Orion Molecular Clouds. OMC-1 lies directly behind M42, while OMC-2 and OMC-3 reside to its north and OMC-4 to its south.
JWST imaged a small piece in the northern part of OMC-2. This region lies 1,270 light-years from Earth, close enough to allow astronomers a detailed view of the early stages of star formation. This specific slice of the cloud spans 2.5 by 1.5 light-years.
A protostar develops in a high-density molecular cloud like OMC-2 when gravity starts to win a tug of war against gas pressure. The nascent star slowly pulls in material from its surroundings, growing more massive while also shrinking in size. To conserve angular momentum, the contracting cloud must spin faster. The infalling matter forms an accretion disk in the budding star’s equatorial plane and, like water circling a drain, the gas continues to accumulate on the stellar embryo.
The disk’s inner part boasts powerful magnetic fields, which channel some of the material into high-speed jets that escape along the protostar’s rotation axis. When these jets collide with their dense surroundings, they create shock waves that heat the gas and cause it to glow.
OMC-2 dazzles
JWST’s infrared eye captures the resulting maelstrom. The jets, which travel hundreds of thousands of miles per hour, create the sharp-edged glows that dot the image. Most of these appear reddish, but you also see a few that veer closer to white. The smaller outflows emanate from younger protostars that have yet to kick into high gear. A small number remain totally hidden — not even JWST can pierce their thick dusty cocoons.
The few “stars” visible in the image, those dots sporting six symmetric diffraction spikes, have largely cleared away their birth clouds. Some may be pre-main sequence stars in OMC-2, while others could lie a bit in the foreground. In either case, they show what the molecular cloud’s protostars will one day become.
Richard Talcott is a former senior editor and current contributing editor of Astronomy.