A star is born: Study reveals complex chemistry inside 'stellar
nurseries'

Date:
February 6, 2023
Source:
University of Colorado at Boulder
Summary:
The universe's carbon atoms complete a journey that spans eons
-- forming in the hearts of dying stars, then becoming a part of
planets and even living organisms. Now, a team has uncovered the
chemistry behind one tiny, but critical, step in this process.


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FULL STORY ==========================================================================
An international team of researchers has uncovered what might be a
critical step in the chemical evolution of molecules in cosmic "stellar nurseries." 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.


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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, published Feb. 6 in the journal Nature Astronomy, reveal how
certain large organic molecules may form inside these clouds. It's one
tiny step in the eons-long chemical journey that carbon atoms undergo -- forming in the hearts of dying stars, then becoming part of planets,
living organisms on Earth and perhaps beyond.

"In these cold molecular clouds, you're creating the first building blocks
that will, in the end, form stars and planets," said Jordy Bouwman,
research associate at the Laboratory for Atmospheric and Space Physics
(LASP) and assistant professor in the Department of Chemistry at the
University of Colorado 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. This chemically complex
environment is an example of what astronomers call an "accreting starless core." Its cloud has begun to collapse, but scientists haven't 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.

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.

"We're only at the start of truly understanding how we go from these
small building blocks to larger molecules," he said. "I think we'll
find that this chemistry is so much more complex than we thought, even
at the earliest stages of star formation." 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 (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 "five-membered ring compounds" because they each contain a ring of carbon atoms shaped like a pentagon.

"Researchers kept detecting these molecules in TMC-1, but their origin
was unclear," Bouwman said.

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

In 2021, researchers using the Yebes 40-metre Radiotelescope 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't require a lot of heat to do so.

"There's no barrier to reaction," Bouwman said. "That means that it
has the potential to drive complex chemistry in cold environments."
Identifying the culprit To find out what kind of complex chemistry was happening in TMC-1, Bouwman and his colleagues -- who hail from the United States, Germany, the Netherlands and Switzerland -- turned to a technique called "photoelectron photoion coincidence spectroscopy." The team used
light generated by a giant facility called a synchrotron 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.

"We knew we were onto something good," Bouwman said.

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.

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 the reactions happening in TMC-1. He wants to examine,
for example, how organic molecules in space also pick up nitrogen atoms --
key components of the DNA and amino acids of living organisms on Earth.

"Our findings may just change the view on what ingredients we have in
the first place to form new stars and new planets," 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 Wu"rzburg in Germany and Paul Scherrer Institute in Switzerland.

* RELATED_TOPICS
o Space_&_Time
# Astrophysics # Stars # Galaxies # Extrasolar_Planets #
Solar_Flare # Astronomy # Space_Exploration # Black_Holes
* RELATED_TERMS
o Atom o Nucleosynthesis o Definition_of_planet
o Extrasolar_planet o Planetary_habitability
o Cosmic_microwave_background_radiation o
Galaxy_formation_and_evolution o Extraterrestrial_life

========================================================================== Story Source: Materials provided by
University_of_Colorado_at_Boulder. Original written by Daniel
Strain. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jordy Bouwman, Morgan N. McCabe, Christopher N. Shingledecker,
Joseph
Wandishin, Virginia Jarvis, Engelbert Reusch, Patrick Hemberger,
Andras Bodi. Five-membered ring compounds from the ortho-benzyne
+ methyl radical reaction under interstellar conditions. Nature
Astronomy, 2023; DOI: 10.1038/s41550-023-01893-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/02/230206130630.htm

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