JWST captured the Serpens Nebula – a region with an exceptional sample of star formation processes

Written By Rosa I Diaz

Astronomers used the James Webb Telescope ( JWST) to look at the core of the Serpens Nebula or Cloud, a region with extreme richness in star formation activity[1]. Using the high resolution and sensitivity in the Infrared (IR) light of this powerful telescope, astronomers can now see the details hidden behind a substantial amount of dust in the region and that obscures the young stellar population there.

Image Credit: NASA, ESA, CSA, K. Pontoppidan (NASA’s JPL) and J. Green (STScI).

Images and spectra in the infrared, submillimeter, millimeter, radio continuum, and X-rays obtained during the last 30 years revealed more than 300 objects in all evolutionary phases. Within a small region of about 1.6 − 2.3 light-years, there are pre-protostellar gaseous condensations; pre-stellar dust condensations; Class 0, Class I, and Class II objects; different evidences of infalling gas; disks; molecular and atomic outflows and jets; clustering of young stellar objects ( YSOs ) in various evolutionary stages, etc., making the Serpens core a laboratory for studies of star formation processes and how these manifest in the observations[2].

In 2007,  observations taken with two space telescopes, Spitzer in the IR and Chandra in X-rays, identified more than 100 YSOs distributed across the whole Serpens core. These observations also sampled the gas in the region, indicating widespread absorption by CO molecules, methanol, and water ice[3.] In these images, the very youngest objects, in the early stages of stellar development, appear as red, orange, and yellow points or features, including jets of material ejected from these young stars. Some mature stars, not in the nebula, appear yellowish due to dust obscuring our view at shorter, bluer wavelengths[4]. This region also includes a population of prenatal stars which are so deeply enshrouded in their dusty cocoons to be completely hidden in this view.

In the southwest region, a concentration of 10 objects align to form a perfect V. This is one of the densest young stellar sub-clusters known as SVS4 and includes a mix of Class I, flat-spectrum, and Class II sources. It also has one of the brightest X-ray sources known among young stars, which astronomers believe might be due to a very active magnetic corona. Another set of observations taken with the ground observatory ESO’s near-IR imager in the J, H, and K bands, show that the stars at the base of this cluster appear embedded in a common faint nebulosity. These stars pop up bright in the JWST image, although some still appear embedded in a colder cloud of dust and molecular gas.

This image, taken with the NASA/ESA Hubble Space Telescope shows the Serpens Nebula, a stellar nursery about 1300 light-years away. Within the nebula, in the upper right of the image, a shadow is created by the protoplanetary disc surrounding the star HBC 672. While the disc of debris is too tiny to be seen even by Hubble, its shadow is projected upon the cloud in which it was born. In this view, the feature — nicknamed the Bat Shadow — spans approximately 200 times the diameter of our own Solar System. A similar looking shadow phenomenon can be seen emanating from another young star, in the upper left of the image. Credit:  NASA, ESA, and STScI

Another spectacular image of this region was taken with the NASA/ESA Hubble Space Telescope in 2018, showing clearly the shadow created by the protoplanetary disc surrounding the star HBC 672. This disk is a debris ring of dust, rock, and ice — nicknamed the Bat Shadow — that spans approximately 200 times the diameter of our own Solar System and is an analog of what the solar system looked like when it was only 1 or 2 million years old. A similar-looking shadow phenomenon appears in another young star in the upper left of the image [5][6]. The presence of a shadow means that the disk is nearly edge-on, but because of the great distance from us, it is too small to be seen by the IR channel of Hubble. However, scientists were able to use the shadow to figure out that the shape of the disk was puffy and full of gas. The Bat Shadow in the JWST image taken in 2024 has a red hue nebulosity. Astronomers should be able to use these observations to provide more clues about the size and composition of dust grains suspended in the disk.

From earlier studies, we know that many of the Serpens objects appear to be binaries or forming part of small sub-clusters. Studies have found that about 35% of the Class I/flat-spectrum sources are binary stars. SVS 20, the object north of SVS 4, is an elliptical eye-like shape with a young binary system in its center. In this case, the two stars in the center have masses between 1 and 4 Msun, and the elliptical nebulosity around can be a disk or a cavity produced by an outflow[3]. The Serpens Nebula, however, lacks any of the massive and incredibly bright stars found in larger star-forming regions like the Orion Nebula. Here, objects seem to have relatively low to moderate mass — some are even very low-mass M stars and/or brown dwarfs.

Image Credit: arXiv:2406.13084v1

The northern area of the JWST image also shows crisp and clear protostellar jets, some of which appeared as blurry shapes in previous Spitzer observations [4]. With the JWST observations, we can see that these jets are abundant and strikingly aligned, probably confirming some of the most intriguing star formation processes involving magnetic fields. In these processes, stars form in filamentary structures and within star-forming cores that cluster along filamentary density enhancements perpendicular to the magnetic lines. The orientations of the jets in the Serpent Cloud are highly aligned and perpendicular to the magnetic field lines of the Serpens filament, just as predicted by theoretical models.

These jets are magnetized outflows of gas, shut out perpendicular to a disk of material around the central protostar. The bright bow-like shapes behind the shocks are produced by the high-velocity material of these jets colliding with nearby and slower-moving gas and dust [7]. The disks around protostars are also features of star formation, and it is thought that the material from the maternal cloud is transferred to the protostar in its center until it eventually reaches enough mass to ignite the gas in the core and give birth to a star.

Jets in other parts of Serpens Cloud do not show this alignment, making astronomers believe this is an evolutionary process. They speculate that in the Northwest region, the protostars might be younger, and the alignment is preserved. In the Southeast region, on the other hand, the disk orientation is maintained, but the spin axes have had time to process or dissociate through dynamic interactions. One way this might happen is when binary stars spin around each other and wobble in orientation, twisting the direction of the outflows over time. Future studies of star-forming filaments with JWST might explain some of these mysteries of the Serpens Cloud and of star formation..

 

References:

Rosa I Diaz
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