July 14, 2024
1 Solar System Way, Planet Earth, USA

Forming stars like old times – Astronomy Now

Did stars form differently 12 billion years ago than they do today? The cosmic environment of the early Universe was metal-poor, meaning it lacked the heavy elements that astronomers call “metals” and that form inside stars. These metals were scarce because not enough time had passed for enough generations of stars to produce them.

Image: NASA/ESA/CSA/STScI/A. Pagan (STScI).

The abundance of these metals in giant clouds of molecular gas is thought to affect star formation, for example by influencing the initial mass function that describes the distribution of stellar masses. In the present-day universe, the initial mass function makes low-mass stars extremely common and high-mass stars extremely rare. In the early universe, however, things might have been different.

Astronomers can investigate this phenomenon in two ways: by observing distant galaxies that remind us of that time with telescopes like JWST. Another way is to look for regions in the local universe that mimic conditions in the early universe. Astronomers have discovered one such region in the star-forming nebula NGC 346 in the Small Magellanic Cloud (SMC). Its metallicity and rapid rate of star formation are consistent with what we would expect from the early universe. Dwarf galaxies like the SMC typically develop late, with current conditions similar to those of galaxies 11 to 12 billion years ago, and so can offer a glimpse into what the past was like.

Previously, astronomers have been able to study higher-mass young stars in NGC 346, but in an ongoing project with JWST, which took this image with its Near Infrared Camera, astronomers can now detect smaller stars down to red dwarfs with just a tenth the mass of the Sun, to see if their formation is affected by the lower metallicity.

In this image, JWST removes gas that is transparent at infrared wavelengths, revealing a skeleton of dusty ribbons that are part of the material that flows toward young stars as they grow.

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