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The Hidden Star Formation in Cluster's Dusty Ribbons

NGC 346, renowned for being one of the most vibrant star-creation zones in nearby galaxies, has been an enigma to scientists. However, recent insights from NASA’s James Webb Space Telescope have begun to unravel its secrets.

NGC 346 is situated within the Small Magellanic Cloud (SMC), a dwarf galaxy in proximity to our Milky Way. The SMC exhibits lower densities of elements heavier than hydrogen or helium, referred to as metals by astronomers, compared to our own galaxy. Given that cosmic dust grains largely consist of these metals, scientists initially expected sparse amounts of detectable dust. However, new information from the Webb Telescope suggests otherwise.

Astronomers chose to investigate this region as the SMC's conditions and metal content align with those of galaxies dating back billions of years, during a universal phase known as "cosmic noon," characterized by peak star formation. Approximately 2 to 3 billion years following the Big Bang, galaxies were producing stars at an accelerated pace. This flurry of star formation continues to shape galaxies that we see today.

"A galaxy during cosmic noon would not host a single NGC 346 like the Small Magellanic Cloud does; it would be home to thousands of such star-creating regions," said Margaret Meixner, an astronomer at the Universities Space Research Association and the head investigator of the research team. "Regardless, even as the sole massive cluster in its galaxy actively forming stars, NGC 346 presents a fantastic opportunity to explore conditions prevalent during the cosmic noon."

By observing protostars in the midst of formation, researchers can determine if the star-creation process in the SMC differs from that in the Milky Way. Previous infrared studies of NGC 346 concentrated on protostars more substantial than approximately 5 to 8 times the mass of our Sun. "With Webb, we can now examine protostars as small as one-tenth the mass of our Sun, to determine if the reduced metal content impacts their formation process," commented Olivia Jones of the United Kingdom Astronomy Technology Centre, Royal Observatory Edinburgh, a co-researcher on the project.

As stars develop, they accumulate gas and dust from the surrounding molecular cloud, which in Webb's imagery can appear as ribbons. This material congregates into an accretion disk that nourishes the central protostar. While astronomers have previously detected gas around protostars within NGC 346, Webb's near-infrared observations mark the first detection of dust in these disks.

"We are witnessing the fundamental constituents of not just stars, but potentially planets as well," said Guido De Marchi of the European Space Agency, a co-researcher on the project. "Given the environmental similarity of the Small Magellanic Cloud to galaxies during the cosmic noon, it’s plausible that rocky planets could have materialized earlier in the universe than we previously believed."

The team also possesses spectroscopic data from Webb’s NIRSpec instrument that they continue to examine. These data are anticipated to provide further insights into the materials accreting onto individual protostars, as well as the immediate surroundings of the protostar.

These findings were presented on January 11 at the 241st meeting of the American Astronomical Society. The observations were carried out as part of program 1227.