Forming stars like the old days

Did stars form differently 12 billion years ago compared to how they form today? The cosmic environment of the early Universe was metal-poor – that is, it was depleted in heavy elements that astronomers call ‘metals’ and that are formed inside stars. These metals were sparse because not enough time had passed for sufficient generations of stars to produce them.

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

It’s thought that the abundance of these metals within giant molecular gas clouds can affect how stars form, for example potentially influencing the initial mass function that describes the distribution of stellar masses. In the present day Universe, the initial mass function leads to low-mass stars being extremely common and high-mass stars being extremely rare. In the early Universe, however, things may have been different.

There’s two ways in which astronomers can investigate this. One way is to observe distant galaxies that harken back to this early age with telescopes such as JWST. Another way is to seek out regions in the local Universe that mimic the conditions of the early Universe. Astronomers have found one such region, in the star-forming nebula NGC 346 in the Small Magellanic Cloud (SMC). Its metallicity and furious rate of star formation match what we would expect from the early Universe. Dwarf galaxies such as the SMC are often late developers, with conditions today similar to those of galaxies from 11–12 billion years ago, and therefore they can provide 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 one-tenth of a solar mass, to see if their formation is affected by the lower metallicity.

In this image, JWST strips away the gas that is transparent at infrared wavelengths, and reveals a skeleton of dusty ribbons that are part of the material that is flowing onto the young stars as they grow.