Abstract The astrophysical sites where r -process elements are synthesized remain mysterious: it is clear that neutron star mergers (kilonovae (KNe)) contribute, and some classes of core-collapse supernovae (SNe) are also possible sources of at least the lighter r -process species. The discovery of 60 Fe on the Earth and Moon implies that one or more astrophysical explosions have occurred near the Earth within the last few million years, probably SNe. Intriguingly, 244 Pu has now been detected, mostly overlapping with 60 Fe pulses. However, the 244 Pu flux may extend to before 12 Myr ago, pointing to a different origin. Motivated by these observations and difficulties for r -process nucleosynthesis in SN models, we propose that ejecta from a KN enriched the giant molecular cloud that gave rise to the Local Bubble, where the Sun resides. Accelerator mass spectrometry (AMS) measurements of 244 Pu and searches for other live isotopes could probe the origins of the r -process and the history of the solar neighborhood, including triggers for mass extinctions, e.g., that at the end of the Devonian epoch, motivating the calculations of the abundances of live r -process radioisotopes produced in SNe and KNe that we present here. Given the presence of 244 Pu, other r -process species such as 93 Zr, 107 Pd, 129 I, 135 Cs, 182 Hf, 236 U, 237 Np, and 247 Cm should be present. Their abundances and well-resolved time histories could distinguish between the SN and KN scenarios, and we discuss prospects for their detection in deep-ocean deposits and the lunar regolith. We show that AMS 129 I measurements in Fe–Mn crusts already constrain a possible nearby KN scenario.
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129 I and 247 Cm in meteorites constrain the last astrophysical source of solar r-process elements
The composition of the early Solar System can be inferred from meteorites. Many elements heavier than iron were formed by the rapid neutron capture process (r-process), but the astrophysical sources where this occurred remain poorly understood. We demonstrate that the near-identical half-lives ( ≃ 15.6 million years ) of the radioactive r-process nuclei iodine-129 and curium-247 preserve their ratio, irrespective of the time between production and incorporation into the Solar System. We constrain the last r-process source by comparing the measured meteoritic ratio 129 I/ 247 Cm = 438 ± 184 with nucleosynthesis calculations based on neutron star merger and magneto-rotational supernova simulations. Moderately neutron-rich conditions, often found in merger disk ejecta simulations, are most consistent with the meteoritic value. Uncertain nuclear physics data limit our confidence in this conclusion.
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- NSF-PAR ID:
- 10251057
- Date Published:
- Journal Name:
- Science
- Volume:
- 371
- Issue:
- 6532
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- 945 to 948
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Meteoritic analysis demonstrates that radioactive nuclei heavier than iron were present in the early Solar System. Among them, 129I and 247Cm both have a rapid neutron-capture process (r process) origin and decay on the same timescale (≃ 15.6 Myr). We show that the 129I/247Cm abundance ratio in the early Solar System (438±184) is immune to galactic evolution uncertainties and represents the first direct observational constraint for the properties of the last r-process event that polluted the pre-solar nebula. We investigate the physical conditions of this event using nucleosynthesis calculations and demonstrate that moderately neutron-rich ejecta can produce the observed ratio. We conclude that a dominant contribution by exceedingly neutron-rich ejecta is highly disfavoured.more » « less
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Abstract With the most trans-iron elements detected of any star outside the solar system, HD 222925 represents the most complete chemical inventory among metal-poor stars enhanced with elements made by the rapid neutron capture (“
r ”) process. As such, HD 222925 may be a new “template” for the observationalr -process, where before the (much higher-metallicity) solarr -process residuals were used. In this work, we test under which conditions a single site accounts for the entire elementalr -process abundance pattern of HD 222925. We found that several of our tests—with the single exception of the black hole–neutron star merger case—challenge the single-site assumption by producing an ejecta distribution that is highly constrained, in disagreement with simulation predictions. However, we found that ejecta distributions that are more in line with simulations can be obtained under the condition that the nuclear data near the secondr -process peak are changed. Therefore, for HD 222925 to be a canonicalr -process template likely as a product of a single astrophysical source, the nuclear data need to be reevaluated. The new elemental abundance pattern of HD 222925—including the abundances obtained from space-based, ultraviolet (UV) data—call for a deeper understanding of both astrophysicalr -process sites and nuclear data. Similar UV observations of additionalr -process–enhanced stars will be required to determine whether the elemental abundance pattern of HD 222925 is indeed a canonical template (or an outlier) for ther -process at low metallicity.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1126/science.aba1111
