You’re looking at NGC 346, a star cluster 210 light-years away that’s vigorously pumping out brand-new stars from a dense cloud of gas and dust. Between 10 and 11 billion years ago, nearly all galaxies in the universe underwent an intense star formation era similar to what we see in NGC 346. This wave of star birth is dubbed the cosmic noon. Since then, the star formation in the universe has gradually diminished, although it is still smoldering in small pockets. By studying NGC 346 and other clusters like it, we can learn more about the cosmic noon and the evolution of galaxies.
To that end, the researchers pointed the James Webb Space Telescope’s NIRCam infrared camera at NGC 346 last year, and announced their preliminary results at the annual meeting of the American Astronomical Society on January 11, 2023.
Located within the Small Magellanic Cloud (SMC), NGC 346 is a dwarf galaxy that, as one of the Milky Way’s closest neighbors, is visible to the naked eye in the Southern Hemisphere. The rest of the SMC is not nearly as active as NGC 346, and this lack of activity is normal for galaxies in the present-day universe.
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Margaret Mixner, principal investigator of the research team, explains that things weren’t always so calm.
“A galaxy in the cosmic afternoon will not have one NGC 346, as it does in the Small Magellanic Cloud,” she said. “But even if NGC 346 is now the only massive, strongly star-forming cluster in its galaxy, it offers us a great opportunity to explore conditions that existed at cosmic noon.”
In particular, SMC has low concentrations of heavy elements (everything heavier than hydrogen and helium). This was also true in the early universe, before stars had time to produce heavier elements through nuclear fusion. The researchers are interested to see how star formation in regions devoid of heavy elements might differ from star formation in the heavy element-rich Milky Way. NIRCam enables them to do this better than ever before, by picking out tiny, tiny stars that previous telescopes didn’t have the resolution to see. “Using Webb, we can investigate even the lightest protostars, which are about a tenth the size of our Sun, to see if their formation process is affected by low metal content,” said Olivia Jones, co-investigator with the program.
Webb also enabled them to see dust in the accretion disk of the SMC’s protostars for the first time. And this means that there is a possibility of the formation of rocky planets, and not just stars and gas giants.
“We’re seeing the building blocks of not only stars, but also potential planets,” said co-investigator Guido De Marchi. “Since the Small Magellanic Cloud has a similar environment to galaxies during the cosmic noon, it is possible that rocky planets formed much earlier in the universe than we thought.”
The team continues to pump out the data collected, including spectroscopy that will provide more information about the exact chemical composition of matter in and around protostars.
In the NIRCam image, the pink gas is hot, energized hydrogen, while the orange gas (as in the upper left) is cold, dense molecular hydrogen. This cold, dense hydrogen is an ideal incubator for star formation. As stars grow, they alter the nebula around them, eroding gas and forming the ridges and ripples that can be seen throughout the cluster.
“Webb inspects NGC 360.” ESA.
Olivia Jones and others. “Detection of dusty young stellar objects below the solar mass in NGC 346 using JWST/NIRCam.” ArXiv preprint.