An international team of physicists compared the results of studies of supernovae and kilonovae with observations from the James Webb Telescope and came to the conclusion that the heaviest chemical elements necessary for our life were formed during astronomical events that are “controlled” by gravitational waves.
All chemical elements heavier than iron arose through astrophysical processes: the thermonuclear p-process, as well as slow (s-process) and fast (r-process) neutron capture. More than 20 elements are considered essential for the existence of life as we know it. Most of these elements have an atomic number above 35, and they formed in supernovae during the p-process and r-process. But there are two elements that are created primarily during the r-process: bromine and iodine. The latter is of particular interest to scientists.

According to calculations by the authors of the new study, which is available as a preprint on arXiv, 96% of the iodine-127 in the Earth’s crust was formed during the R process. The conditions required for launch are extremely extreme. A high concentration of free neutrons is required in proportion to the number of nuclei that can be “attached” to form heavier elements. Although the right conditions exist for a supernova, there are some problems. First, they are literally life-threatening when they occur near the human world. Probably they caused many mass extinctions on our planet. Scientists say such supernovae occur within 20 parsecs of Earth every hundreds of millions of years. Second, it is not entirely clear how successful the R process is in supernovae and how widely the new elements are scattered. Therefore, in addition to supernovae, scientists also study kilonovae, which are the mergers of two neutron stars or one neutron star and a black hole. Generally, it will have the same “radius of destruction” as a supernova, unless the planet is lucky enough to be in the path of a gamma-ray burst from the event. However, because it occurs less frequently, it is less dangerous in the long term. The study’s authors hypothesize that kilonovas produce important elements and that gravitational waves cause these phenomena. The first indirect evidence that neutron stars collide to lose energy through gravitational waves came from an analysis of observations of the pulsar PSR B1913+16. This was directly confirmed by studying gravitational waves from the merger of her two neutron stars in GW170817. In 2023, another group of scientists analyzed the aforementioned GW170817 signal from LIGO data and concluded that tellurium and lanthanides were produced by this neutron star collision. Researchers who used James Webb’s data to study the kilonova that produced the gamma-ray burst GRB 230307A came to the same conclusion. This means that tellurium is definitely present in the chironovae. The R process naturally produces a group of elements with abundance peaks corresponding to stable atomic nuclei with a magic number of neutrons. Because tellurium and iodine are in the same peak, the researchers say the described chironovae must have produced iodine in addition to tellurium. The authors of the new study proposed testing this hypothesis by examining the levels of iodine-129 in the lunar regolith. Previously, he and his colleagues had proposed testing plutonium-244 levels in the lunar regolith and comparing them to plutonium levels in seafloor sedimentary rocks over the past 10 million years. All of this is to calculate the contribution of chironovae to the abundance of heavy elements on Earth. Iodine is more volatile than plutonium and other heavy elements formed during the R process. This affects the nature of iodine-bearing interstellar dust and its spread into space. Therefore, while the plutonium content in the lunar regolith is still predictable, the iodine abundance is more difficult to predict. But finding iodine-129 in the lunar regolith would confirm that this element was indeed formed in the chironovae and scattered over relatively long distances. Note that this is actually the first method proposed by scientists to test the influence of chironovae on the formation of heavy elements.

source: https://arxiv.org/abs/2402.03593