For carbon, the basis of life, to be able to form in the
stars, a certain state of the carbon nucleus plays an essential role. In
cooperation with U.S.
colleagues, physicists from the Univ.
of Bonn and
Ruhr-Universität Bochum have been able to calculate this legendary carbon
nucleus, solving a problem that has kept science guessing for more than 50
years. The researchers published their results in Physical Review Letters.
“Attempts to calculate the Hoyle state have been
unsuccessful since 1954,” said Professor Dr. Ulf-G. Meißner (Helmholtz-Institut
für Strahlen- und Kernphysik der Universität Bonn). “But now, we have done it!” The Hoyle
state is an energy-rich form of the carbon nucleus. It is the mountain pass
over which all roads from one valley to the next lead: From the three nuclei of
helium gas to the much larger carbon nucleus. This fusion reaction takes place
in the hot interior of heavy stars. If the Hoyle state did not exist, very
little carbon or other higher elements such as oxygen, nitrogen, and iron could
have formed. Without this type of carbon nucleus, life probably also would not
have been possible.
The search for the “slave transmitter”
The Hoyle state had been verified by experiments as early as 1954, but
calculating it always failed. For this form of carbon consists of only three,
very loosely linked helium nuclei—more of a cloudy diffuse carbon nucleus. And
it does not occur individually, only together with other forms of carbon. “This
is as if you wanted to analyze a radio signal whose main transmitter and
several slave transmitters are interfering with each other,” explained Prof.
Dr. Evgeny Epelbaum (Institute
of Theoretical Physics II
at Ruhr-Universität Bochum). The main transmitter is the stable carbon nucleus
from which humans—among others—are made. “But we are interested in one of the
unstable, energy-rich carbon nuclei; so we have to separate the weaker radio
transmitter somehow from the dominant signal by means of a noise filter.”
What made this possible was a new, improved calculating
approach the researchers used that allowed calculating the forces between
several nuclear particles more precisely than ever. And in JUGENE, the
supercomputer at Forschungszentrum Jülich, a suitable tool was found. It took
JUGENE almost a week of calculating. The results matched the experimental data
so well that the researchers can be certain that they have indeed calculated
the Hoyle state.
More about how the Universe came into existence
“Now we can analyze this exciting and essential form of the carbon nucleus in
every detail,” explained Prof. Meißner. “We will determine how big it is, and
what its structure is. And it also means that we can now take a very close look
at the entire chain of how elements are formed.”
In future, this may even allow answering philosophical
questions using science. For decades, the Hoyle state was a prime example for
the theory that natural constants must have precisely their experimentally
determined values, and not any different ones, since otherwise we would not be
here to observe the Universe (the anthropic principle). “For the Hoyle state
this means that it must have exactly the amount of energy it has, or else, we
would not exist,” said Prof. Meißner. “Now we can calculate whether—in a changed
world with other parameters—the Hoyle state would indeed have a different
energy when comparing the mass of three helium nuclei.” If this is so, this
would confirm the anthropic principle.
The study was jointly conducted by the Univ. of Bonn,
Ruhr-Universität Bochum, North Carolina State Univ., and Forschungszentrum Jülich.
