Tiny Quantum Ghosts Might Be Creating Brand-New Elements
Although the periodic table is filled with elements, nuclear fusion at the center of stars can only produce elements with atomic masses lower than iron—after than, neutron captures processes known as r-process and s-process produce the rest.
However, for nearly 50 years, scientists have theorized a third process, known as intermediate neutron-capture process (i-process) that falls somewhat between these two processes, and recently astrophysicists have revived the idea to explain strange mysteries around carbon-enhanced metal-poor stars.
Now a study from the University of Wisconsin-Madison dives into the quantum physics of this i-process and discovers that its possible through neutrino-neutrino entanglement.
In the beginning, there was lots and lots of hydrogen and helium—that is until the fiery fusion furnaces of primordial stars began churning out heavier elements. Nuclear fusion can form elements all the way until an atom contains 26 protons and 30 neutrons (aka Iron) until it inevitably collapses. Of course, there’s just one problem. If you’ve happened to glance at a periodic table lately, there’s many more elements with atomic masses far beyond iron. So what gives?
Turns out there’s another element-producing process at work, and it’s called neutron capture, or nucleosynthesis. This process breaks down into two different types, which are called rapid neutron-capture process (r-process) and slow neutron-capture process (s-process), and each are roughly responsible for creating half of the known elements beyond iron. As their names suggest, these processes occur in very different environments. R-process requires a high density of free neutrons (think neutron star mergers or supernova collapses) while s-process occurs in asymptotic giant branch (AGB) stars and possible metal-poor massive stars via radioactive decay.
But as with most things in astrophysics, things are not quite so black and white. Back in 1977, scientists proposed a third process, known as the intermediate-process (i-process), that exists sort of in between both r- and s-processes. The idea faded with time but has regained attention in recent years due to the enigma known as carbon-enhanced metal-poor (CEMP) r/s stars, which produce abundances of carbon and heavy elements associated with both processes. Now, a new study from the University of Wisconsin—Madison investigates how exactly such an i-process would work, and the solution to this very big mystery veers into the very small quantum world.
“When a supernova collapse occurs, you start with a big star, which is gravitationally bound, and that binding has energy,” UW-Madison’s Baha Balantekin, a co-author of a paper on the i-process published in The Astrophysical Journal, said in a press statement. While the i-process is a nucleosynthesis middle child, one aspect is shares with r-process is that it only occurs in similarly violent conditions. “When it collapses, that energy has to be released, and it turns out that energy is released in neutrinos.”
Its when those neutrinos experience quantum entanglement due to interactions in a supernova, that the i-process can take over and produce heavy elements. This entanglement means the two neutrinos “remember” each other no matter how far apart they may be. Using well-known rates of neutron capture, catalogs of atomic spectra of various stars, and data surrounding neutrino production via supernova, the team ran simplified simulations (supernovae produce 10^58 neutrinos after all) and arrive at differing abundances depending on whether these neutrinos were entangled or not.
“We have a system of, say, three neutrinos and three antineutrinos together in a region where there are protons and neutrons and see if that changes anything about element formation,” Balantekin says. “We calculate the abundances of elements that are produced in the star, and you see that the entangled or not entangled cases give you different abundances.”
There are a few things about this hypothesis that still need to be tested—chief among them is that neutrino-neutrino interactions are largely hypothetical at this point. However, this new process could help further explain how something came from nothing.
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