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Context. The 26 Al short-lived radioactive nuclide is the source of the observed galactic diffuse γ -ray emission at 1.8 MeV. While different sources of 26 Al have been explored, such as asymptotic giant branch stars, massive stellar winds, and supernovae, the contribution of very massive stars has not been studied so far. Aims. We study the contribution of the stellar wind of very massive stars, here, stars with initial masses between 150 and 300 M ⊙ , to the enrichment in 26 Al of the galactic interstellar medium. Methods. We studied the production of 26 Al by studying rotating and non-rotating very massive stellar models with initial masses between 150 and 300 M ⊙ for metallicities Z = 0.006, 0.014, and 0.020. We compared this result to a simple Milky Way model and took the metallicity and the star formation rate gradients into account. Results. We obtain that very massive stars in the Z = 0.006 − 0.020 metallicity range might be very significant contributors to the 26 Al enrichment of the interstellar medium. Typically, the contribution of the winds of massive stars to the total quantity of 26 Al in the Galaxy increases by 150% when very massive stars are considered. Conclusions. Despite their rarity, very massive stars might be important contributors to 26 Al and might overall be very important actors for nucleosynthesis in the Galaxy.
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This content will become publicly available on March 1, 2026
The aluminium-26 distribution in a cosmological simulation of a Milky Way-type Galaxy
Context. The 1.8 MeVγ-rays corresponding to the decay of the radioactive isotope26Al (with a half-life of 0.72 Myr ) have been observed by the SPI detector on the INTEGRAL spacecraft and extensively used as a tracer of star formation and current nucleosynthetic activity in the Milky Way Galaxy. Further information is encoded in the observation related to the higher26Al content found in regions of the Galaxy with the highest line-of-sight (LoS) velocity relative to an observer located in the Solar System. However, this feature remains unexplained. Aims. We ran a cosmological “zoom-in” chemodynamical simulation of a Milky Way-type galaxy, including the production and decays of radioactive nuclei in a fully self-consistent way. We then analyzed the results to follow the evolution of26Al throughout the lifetime of the simulated galaxy to provide a new method for interpreting the26Al observations. Methods. We included the massive star sources of26Al in the Galaxy and its radioactive decay into a state-of-the-art galactic chemical evolution model, coupled with cosmological growth and hydrodynamics. This approach allowed us to follow the spatial and temporal evolution of the26Al content in the simulated galaxy. Results. Our results are in agreement with the observations with respect to the fact that gas particles in the simulation with relatively higher26Al content also have the highest LoS velocities. On the other hand, gas particles with relatively lower26Al content (i.e., not bright enough to be observed) generally display the lowest LoS velocities. However, this result is not conclusive because the overall rotational velocity of our simulated galaxy is higher than that observed for cold CO gas in the Milky Way Galaxy. Furthermore, we found no significant correlation between gas temperature, rotational velocity, and26Al content at any given radius. We also found the presence of transient26Al-rich spots at low LoS velocities and we show that one such spot had been captured by the INTEGRAL/SPI data. Based on our model, we present a prediction for the detection of 1.8 MeVγ-rays by the future COSI mission. We find that according to our model, the new instrument will be able to observe similar26Al-emission patterns to those seen by INTEGRAL/SPI.
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- Award ID(s):
- 1927130
- PAR ID:
- 10649196
- Publisher / Repository:
- EDP Sciences
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 695
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A190
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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