Sextans A PAHs pull-out (NIRCam and MIRI image)

Using the NASA/ESA/CSA James Webb Space Telescope, astronomers have spotted two rare kinds of dust in the dwarf galaxy Sextans A, one of the most chemically primitive galaxies near the Milky Way. The finding of metallic iron dust and silicon carbide (SiC) produced by aging stars, along with tiny clumps of carbon-based molecules, shows that even when the Universe had only a fraction of today’s heavy elements, stars and the interstellar medium could still forge solid dust grains. This research with Webb is reshaping ideas about how early galaxies evolved and developed the building blocks for planets.

Webb’s data of the dwarf galaxy Sextans A has revealed polycyclic aromatic hydrocarbons (PAHs), large carbon-based molecules that can be a signifier of star formation. In the above image, the inset at the top right zooms in on those PAHs, which are represented in green. In Sextans A, the PAHs are clumpy and relatively small.

Sextans A is a nearby galaxy that is chemically primitive, meaning it has a very low content of metals heavier than helium and hydrogen. It resembles galaxies that filled the early Universe, before stars had a chance to enrich the space with ‘metals’ like oxygen and iron. With the new discovery from Webb, Sextans A is now the lowest-metallicity galaxy ever found to contain PAHs.

This image was created with Webb data from proposal: 2391 (PI: J. Roman-Duval). More information about this result can be found here.

[Image description: A region of space is filled with stars and clumps of glowing orange and tan dust. A small portion of the sky at the center of the image is outlined with a white box. Lines extend from the corner of the box to the inset panel at the top right showing a magnified version of the outlined portion of the image. In the inset, there are smatterings of dim whitish-blueish stars and about seven glowing red orbs across the center in a line. Also across the center of the inset is a green glow. The background of the image is filled with stars and galaxies of various shapes and colors.]