You’re looking at NGC 346, a star cluster 210 light years away that is energetically 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 era of intense star formation similar to what we see in NGC 346. This flurry of stellar birth is poetically nicknamed cosmic noon. Since then, star formation in the Universe has gradually dwindled, though it still blazes away in small pockets. By studying NGC 346 and other clusters like it, we can learn more about the era of cosmic noon and the evolution of galaxies.
To that end, researchers pointed the James Webb Space Telescope’s NIRCam infrared camera at NGC 346 last year, and they announced their preliminary findings at the American Astronomical Society’s annual meeting on January 11, 2023.
NGC 346, a star-forming cluster within the Small Magellanic Cloud, as seen by JWST’s NIRCam. Credits: NASA, ESA, CSA, O. Jones (UK ATC), G. De Marchi (ESTEC), and M. Meixner (USRA). Image processing: A. Pagan (STScI), N. Habel (USRA), L. Lenkic (USRA) and L. Chu (NASA/Ames).
NGC 346 lies within the Small Magellanic Cloud (SMC), a dwarf galaxy that, as one of the Milky Way’s nearest 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 that lack of activity is normal for galaxies in the present-day Universe.
Margaret Meixner, principal investigator of the research team, explains that things weren’t always so calm.
“A galaxy during cosmic noon wouldn’t have one NGC 346, as the Small Magellanic Cloud does; it would have thousands,” she said. “But even if NGC 346 is now the one and only massive cluster furiously forming stars in its galaxy, it offers us a great opportunity to probe the conditions that were in place at cosmic noon.”
In particular, the SMC has low concentrations of heavy elements (everything heavier than hydrogen and helium). This was also true of the early Universe, before stars had had time to churn out heavier elements through nuclear fusion. The researchers are interested in seeing how star formation in regions without heavy elements might differ from star formation in the heavy-element-rich Milky Way. NIRCam enables them to do that better than ever before, by picking out tiny young stars that previous telescopes haven’t had the resolution to see. “With Webb, we can probe down to lighter-weight protostars, as small as one tenth of our Sun, to see if their formation process is affected by the lower metal content,” said Olivia Jones, a co-investigator on the program.
Webb also enabled them to see dust in the accretion disk of protostars in the SMC for the first time. That means there is potential for the formation of rocky planets, rather than just stars and gas giants.
“We’re seeing the building blocks, not only of stars, but also potentially of planets,” said co-investigator Guido De Marchi. “And since the Small Magellanic Cloud has a similar environment to galaxies during cosmic noon, it’s possible that rocky planets could have formed earlier in the Universe than we might have thought.”
The team is continuing to pour over the data collected, including a spectroscopic analysis that will provide more information about the exact chemical makeup of the material in and around the protostars.
In the NIRCam image, the pink gas is hot, energized hydrogen, while the orange gas (like in the top left) is cold, dense, molecular hydrogen. This cold, dense hydrogen is a perfect incubator for star formation. As the stars grow, they change the nebula around them, eroding gas and forming the ridges and ripples seen throughout the cluster.