Scientists have made a fascinating discovery at the center of the Milky Way.
Erythrulose, a sugar typically found in raspberries, kiwis, and other red fruits, has also been detected in a vast molecular cloud of gas and dust located near the galaxy’s core, approximately 26,745 light-years from Earth. This is the first instance of a sugar being identified in interstellar space. The findings have been detailed in Nature Astronomy.
The intriguing question is: How did this sugar appear there? Sugars play a crucial role in life as we know it, serving as energy reserves and as components in the formation of DNA and RNA. However, they are relatively delicate and not easily produced from scratch, whether in deep space or on the primordial Earth. Molecular clouds, described by Izaskun Jiménez-Serra, the study’s lead author and an astrochemist at the Spanish National Research Council and the National Institute of Aerospace Technology’s Center for Astrobiology in Spain, as “huge chemical factories,” offer a potential pathway for sugar creation. These clouds can also act as stellar nurseries, fostering the birth of new stars and planets.
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The molecular cloud, designated G+0.693-0.027, where Jiménez-Serra and her team found the sugar, is abundant in chemicals and serves as “an excellent astronomical lab where we can look for new molecular species,” according to Jiménez-Serra. The cloud’s cold and dark interior, filled with dust, is crucial. This dust provides surfaces for atoms and molecules to adhere to, enabling them to grow larger and more complex. It also shields them from ultraviolet radiation and other high-energy light that could disassemble larger compounds during their formation. As one moves deeper into the cloud, the dust thickens, blocking more radiation, cooling temperatures, and coating dust grains with water and carbon dioxide ices, as well as increasingly complex molecules.
Jiménez-Serra and her colleagues utilized two large radio telescopes in Spain—the Yebes 40-meter dish and the IRAM 30-meter dish—to penetrate the dusty veil of G+0.693-0.027 and explore its intricate cosmic chemistry. Unlike higher-energy light, radio waves can pass through massive clouds of gas and dust unharmed, and some of these radio waves originate from the molecules formed within the cloud. Displaced from their dust-grain habitats by shock waves from nearby supernovae and other phenomena, these molecules can emit a faint but detectable radio signal as they rotate. Each molecule leaves a unique barcodelike pattern on this light, which astronomers can observe by breaking the light into its component colors.
These patterns resemble “a weird-looking comb where the positions of the teeth on the comb represent the frequencies at which a molecule broadcasts,” explains Nick Indriolo, an astronomer at the Space Telescope Science Institute in Baltimore who studies the interstellar medium and was not part of the study. Identifying individual molecules is complex because hundreds of other molecules in the cloud might be emitting signals simultaneously.
To pinpoint any specific molecule, scientists must first determine its unique light pattern by vaporizing the molecules in a laboratory on Earth. According to Jiménez-Serra, sugars have been challenging to measure due to their syrupy liquid form. A new method has stabilized sugar by mixing it with talcum powder to make a solid that, when vaporized with a laser, produces a diagnostic light pattern.
Utilizing this critical information, Jiménez-Serra and her team examined their data from G+0.693-0.027 for evidence of sugar. They discovered numerous indications of erythrulose with four carbon atoms but found surprisingly little evidence of sugars containing three carbon atoms in the same area—challenging a common assumption in astrochemistry that these molecules form by adding one carbon atom at a time. Instead, the team suggests that erythrulose might have originated from glycolaldehyde and ethylene glycol, two molecules also found in the cloud, each possessing a pair of carbon atoms. The researchers are currently conducting follow-up experiments to search for more complex sugars and assess how these delicate molecules react to ultraviolet light.
“Over 300 molecules have been identified in space,” Indriolo notes. While most are toxic to humans, astronomers are uncovering more compounds that could be precursors to life as they delve deeper into molecular clouds’ hidden cores. The essential ingredients for biology appear to emerge even in the universe’s most inhospitable regions. “It was only hypothesized that sugars can form in the regions of space that will eventually give rise to new stars and planets,” Indriolo says. “But now we know that sugars can form in these regions.”
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