Complex Molecules Detected in Ancient Galaxy Near The Dawn of Time

The James Webb Space Telescope has made an astounding discovery in a galaxy hanging out in the early Universe, less than 1.5 billion years after the Big Bang.

From light that traveled for over 12 billion years from a galaxy known as SPT0418-47, astronomers teased out the spectral signal of complex molecules – the polycyclic aromatic hydrocarbons (PAHs) that make up some of the dust grains in the clouds that drift between the stars, soaking up the light and re-emitting it at infrared wavelengths.

This dust suggests a rapid rate of star formation, which is typical for a galaxy from this early era of the universe. But the dust is not evenly distributed, and that suggests that this star creation may be traced to multiple areas within the galaxy, according to a team led by astronomer Justin Spilker of Texas A&M University.

And the capacity to perform such a comprehensive survey of such a distant galaxy is honestly pretty danged mind-blowing.

"Here we present James Webb Space Telescope observations that detect the 3.3-micrometer PAH feature in a galaxy observed less than 1.5 billion years after the Big Bang. According to the researchers, star formation predominates infrared emission throughout the galaxy rather than black hole accretion because of the high equivalent width of the PAH feature.

"Our observations demonstrate that differences in emission from PAH molecules and large dust grains are a complex result of localized processes within early galaxies."

Despite its lofty tone, polycyclic aromatic hydrocarbons are not extremely uncommon. They are as prevalent as soot on Earth. because of the soot on them. They belong to a group of organic compounds that can develop when organic matter is compressed and heated and contain a ring of carbon atoms. Coal includes PAHs; so does smoke, smog, and crude oil.

As far as we know, the majority of the PAHs in the universe have non-biological origins, but the origins of PAHs can also be non-biological. And there are a lot of them out there.

Previous work estimates roughly 15 percent of all carbon between the stars in galaxies like ours is wrapped up in PAHs. They are regarded as a pretty accurate tracer of star formation, with the majority of that material drifting between the stars as dust in the interstellar medium.

Although we have found PAHs in other galaxies, it is much more difficult to find them in very distant galaxies. These molecules absorb light and re-emit it in infrared wavelengths, and previous infrared telescopes had vastly limited sensitivity and coverage. However, we now have the JWST, the most powerful space telescope ever built, strongest in infrared wavelengths.

But on its own, that isn't nearly enough. To make such an in-depth observation, JWST had to make use of gravitational lensing, a peculiarity of physics. This is a gravitational curvature of space-time that occurs around massive objects in the Universe. Imagine a bowling ball put on a trampoline: In reaction to the weight, the trampoline's fabric expands and warps.

Space-time does something similar around massive objects such as galaxies and galaxy clusters, but there's a bonus. Because space-time is distorted and stretched, any light moving through it likewise becomes deformed, amplified, and occasionally duplicated. By effectively using these lenses as a form of cosmic magnifying glass, we can greatly increase the power of our telescopes.

Between us and SPT0418-47 is another galaxy, at a distance of around 3 billion light-years, providing that lensing oomph. This means when JWST took observations of the galaxy as part of the TEMPLATES Early Release Science program, it was able to get enough detail that Spilker and his colleagues could tease out the spectral signature of the light emitted by PAHs at a mid-infrared wavelength of 3.3 micrometers.

This constitutes the most distant detection to date of complex aromatic molecules, and although there's a lot we still don't know – the reason for the uneven distribution of PAHs throughout the galaxy is unknown – it bodes excitingly well for future studies of the evolution of galaxies in the early Universe.

The research has been published in Nature.