Researchers Reveal the Origin Story for Carbon-12, a Building Block for Life
With the
help of the world’s most powerful supercomputer and new artificial intelligence
techniques, an international team of researchers has theorized how the extreme
conditions in stars produce carbon-12, which they describe as “a critical
gateway to the birth of life.”
From: Iowa State University
Ames, Iowa, May 10,
2022 -- The researchers’ fundamental question: “How does the cosmos produce
carbon-12?” said James Vary, a professor of physics and astronomy at
Iowa State University and a longtime member of the research collaboration.
“It turns out it’s not
easy to produce carbon-12,” Vary said.
It takes the extreme
heat and pressures inside stars or in stellar collisions and explosions to
create emergent, unstable, excited-state carbon nuclei with three loosely
linked clumps, each with two protons and two neutrons. A fraction of those
unstable carbon nuclei can shoot off a little extra energy in the form of gamma
rays and become stable carbon-12, the stuff of life.
A paper recently
published by the online journal Nature Communications describes
the researchers’ supercomputer simulations and resulting theory for the nuclear
structure of carbon that favors its formation in the cosmos. The corresponding
author is Takaharu Otsuka of the University of Tokyo, the RIKEN Nishina Center
for Accelerator-Based Science and the Advanced Science Research Center of the
Japan Atomic Energy Agency.
The paper describes how
alpha particles – helium-4 atoms, with two protons and two neutrons – can
cluster to form much heavier atoms, including an unstable, excited carbon-12
state known as the Hoyle state (predicted by theoretical astrophysicist Fred
Hoyle in 1953 as a precursor to life as we know it).
The researchers write
that this alpha-particle clustering “is a very beautiful and fascinating idea
and is indeed plausible because the (alpha) particle is particularly stable
with a large binding energy.”
To test the theory, the
researchers ran supercomputer simulations, including calculations on the Fugaku
supercomputer at the RIKEN Center for Computational Science in Kobe, Japan.
Fugaku is listed as the most powerful supercomputer in the world and is three
times more powerful than No. 2, according to the latest TOP500
supercomputer rankings.
Vary said the
researchers also did their work ab initio, or from first principles, meaning
their calculations were based on known science and didn’t include additional
assumptions or parameters.
They also developed
techniques in statistical learning, a branch of computational artificial
intelligence, to reveal alpha clustering the Hoyle state and the eventual
production of stable carbon-12.
Vary said the team has
worked for more than a decade to develop its software, refine its supercomputer
codes, run its calculations and work out smaller problems while building up to
the current work.
“There’s a lot of
subtlety – a lot of beautiful interactions going on in there,” Vary said.
All the calculations,
physical quantities and theoretical subtlety match what experimental data there
is in this corner of nuclear physics, the researchers wrote.
So they think they have
some basic answers about the origins of carbon-12. Vary said that should lead
to more studies looking for “fine-grain detail” about the process and how it
works.
Was carbon production,
for example, mostly the result of internal processes in stars? Vary asked. Or
was it supernova star explosions? Or collisions of super-dense neutron stars?
One thing is now clear
to the researchers: “This nucleosynthesis in extreme environments produces a
lot of stuff,” Vary said, “including carbon.”
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