Smoke molecules detected in distant galaxy using James Webb

7 Jun 2023

A galaxy (in blue) helped to give the JWST a better view of organic molecules (bright orange spots) in a second galaxy. Image: J Spilker/S Doyle, NASA, ESA, CSA

The PAH compounds detected by the James Webb telescope are the earliest known, pushing back the record by a billion years.

Astronomers have discovered smoke molecules in a distant galaxy, the first time such molecules have been spotted so far away.

Using the powerful James Webb Space Telescope, the international team were able to detect polycyclic aromatic hydrocarbons (PAHs) – chemical compounds found in soot or smoke – in the galaxy known as SPT0418-47, indicating that there are stars forming wherever they are present.

SPT0418-47 is 12.3bn light years away from the Earth. This means that the way it appears through the James Webb now is the way it was less than 1.5bn year after the Big Bang.

“It’s remarkable that the universe can make really large, complex molecules very quickly after the Big Bang. This pushes back the old record for detections like this by about an extra billion years,” Justin Spilker, lead author of the study, was quoted as saying by

“The molecules we found aren’t simple things like water or carbon dioxide. We’re talking about big, floppy molecules with dozens or hundreds of atoms in them.”

Spilker and his team published their findings in Nature earlier this week. The study shows the sheer power of the James Webb, even though the spectrometer aboard the telescope that made the measurement has experienced a “sudden and surprising degradation” in performance.

‘The molecules are mysterious still’

The measurements were also helped by the fact that the galaxy in question lies behind another, closer galaxy, whose gravity bends and distorts the light from SPT0418-47, making it some 30 times brighter than it would otherwise appear. This effect is called gravitational lensing.

“Everywhere we see the molecules, there are stars forming, but there are also parts in that ring where there are stars forming where we don’t see the molecules,” Spilker said of the molecules that appear as bright patches in the galaxy’s ring. “That’s the part we don’t really understand yet.”

The study also notes that SPT0418-47 was already the size of our Milky Way galaxy when the universe was just 10pc of its current age, indicating that it was busy churning out stars in the early universe. “[The galaxy] must have basically formed on overdrive,” Spilker added.

While earlier studies of the galaxy had found areas where stars might have been forming, polycyclic aromatic hydrocarbons have never been detected before because the molecules are hard to find without infrared wavelengths – something the James Webb excels at.

Such molecules have been observed in nearby galaxies, but the latest findings may be an important clue to how these molecules form, according to Karin Sandstrom, an astronomer at the University of California San Diego.

“[The molecules] are quite mysterious still, and we don’t fully understand how they form even in the Milky Way,” she said.

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Vish Gain is a journalist with Silicon Republic