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An international team of researchers has uncovered what might be a critical step in the chemical evolution听of molecules in cosmic 鈥渟tellar nurseries.鈥� In these vast clouds of cold gas and dust in space, trillions of molecules swirl together over millions of years. The collapse of these interstellar clouds eventually gives rise to young stars and planets.

Like human bodies, stellar nurseries contain a lot of organic molecules, which are made up mostly of carbon and hydrogen atoms. The group's results, , reveal how certain large organic molecules may form inside these clouds. It鈥檚 one tiny step in the eons-long chemical journey that carbon atoms undergo鈥攆orming in the hearts of dying stars, then becoming part of planets, living organisms on Earth and perhaps beyond.

鈥淚n these cold molecular clouds, you鈥檙e creating the first building blocks that will, in the end, form stars and planets,鈥� said Jordy Bouwman, research associate at the (LASP) and assistant professor in the Department of Chemistry at CU Boulder.

For the new study, Bouwman and his colleagues took a deep dive into one stellar nursery in particular: the Taurus Molecular Cloud (TMC-1). This region sits in the constellation Taurus and is roughly 440 light years (more than 2 quadrillion miles) from Earth. The chemically complex environment is an example of what astronomers call an 鈥渁ccreting starless core.鈥� Its cloud has begun to collapse, but scientists haven鈥檛 yet detected embryonic stars emerging inside it.

The team's findings hinge on a deceptively simple molecule called ortho-benzyne. Drawing on experiments on Earth and computer simulations, the researchers showed that this molecule can readily combine with others in space to form a wide range of larger organic molecules.听

Small building blocks, in other words, become big building blocks.

And, Bouwman said, those reactions could be a sign that stellar nurseries are a lot more interesting than scientists give them credit for.

鈥淲e鈥檙e only at the start of truly understanding how we go from these small building blocks to larger molecules,鈥� he said. 鈥淚 think we鈥檒l find that this chemistry is so much more complex than we thought, even at the earliest stages of star formation.鈥�

Fateful observation

Bouwman is a cosmochemist, studying a field that blends chemistry and astronomy to understand the churning chemical reactions that happen deep in space.

On the surface, he said, cold molecular clouds might not seem like a hotbed of chemical activity. As their name suggests, these galactic primordial soups tend to be frigid, often hovering around -263 degrees Celsius听(about -440 degrees Fahrenheit), just 10 degrees above absolute zero. Most reactions need at least a little bit of heat to get a kick-start.

But cold or not, complex chemistry seems to be happening in stellar nurseries. TMC-1, in particular, contains surprising concentrations of relatively large organic molecules with names like fulvenallene and 1- and 2-ethynylcyclopentadiene. Chemists call them 鈥渇ive-membered ring compounds鈥� because they each contain a ring of carbon atoms shaped like a pentagon.

鈥淩esearchers kept detecting these molecules in TMC-1, but their origin was unclear,鈥� Bouwman said.

Now, he and his colleagues think they have an answer.听

In 2021, researchers using the in Spain found an unexpected molecule hiding in the clouds of gas of TMC-1: ortho-benzyne. Bouwman explained that this small molecule, made up of a ring of six carbon atoms with four hydrogens, is one of the extroverts of the chemistry world. It easily interacts with a number of other molecules and doesn鈥檛 require a lot of heat to do so.

鈥淭here's no barrier to reaction,鈥� Bouwman said. 鈥淭hat means it has the potential to drive complex chemistry in cold environments.鈥�

Identifying the culprit

To find out what kind of complex chemistry was happening in TMC-1, Bouwman and his colleagues鈥攚ho hail from the United States, Germany, the Netherlands and Switzerland鈥攖urned to a technique called 鈥減hotoelectron photoion coincidence spectroscopy.鈥� The team used light generated by a giant facility called a synchotron light source to identify the products of chemical reactions. They saw that ortho-benzyne and methyl radicals, another common constituent of molecular clouds, readily combine to form larger and more complex organic compounds.听

鈥淲e knew we were onto something good,鈥� Bouwman said.听

The team then drew on computer models to explore the role of ortho-benzyne in a stellar nursery spread out over several light-years deep in space. The results were promising: The models generated clouds of gas containing roughly the same mix of organic molecules that astronomers had observed in TMC-1 using telescopes.听

Ortho-benzyne, in other words, seems to be a prime candidate for driving the gas-phase organic chemistry that occurs within these stellar nurseries, Bouwman said.

He added that scientists still have a lot of work to do to fully understand all of the reactions happening in TMC-1. He wants to examine, for example, how organic molecules in space also pick up nitrogen atoms鈥攌ey components of the DNA and amino acids of living organisms on Earth.听

鈥淥ur findings may just change the view on what ingredients we have in the first place to form new stars and new planets,鈥� Bouwman said.

Co-authors on the new paper include researchers at Leiden University in the Netherlands, Benedictine College in the U.S., the University of W眉rzburg in Germany and Paul Scherrer Institute in Switzerland.