THE SUPERNOVA TRIGGERED FORMATION AND ENRICHMENT OF OUR SOLAR SYSTEM

摘要

We investigate the enrichment of the pre-solar cloud core with short-lived radionuclides, especially 26Al. The homogeneity and the surprisingly small spread in the ratio 26Al/27Al? observed in the overwhelming majority of calcium-aluminium-rich inclusions in a vast variety of primitive chondritic meteorites places strong constraints on the formation of the solar system. Freshly synthesized radioactive 26Al? has to be included and well mixed within 20 kyr. After discussing various scenarios including X-winds, asymptotic giant branch stars, and Wolf-Rayet stars, we come to the conclusion that triggering the collapse of a cold cloud core by a nearby supernova (SN) is the most promising scenario. We then narrow down the vast parameter space by considering the pre-explosion survivability of such a clump as well as the cross-section necessary for sufficient enrichment. We employ numerical simulations to address the mixing of the radioactively enriched SN gas with the pre-existing gas and the forced collapse within 20 kyr. We show that a cold clump of 10 M ☉ at a distance of 5 pc can be sufficiently enriched in 26Al?and triggered into collapse fast enough—within 18 kyr after encountering the SN shock—for a range of different metallicities and progenitor masses, even if the enriched material is assumed to be distributed homogeneously in the entire SN bubble. In summary, we envision an environment for the birthplace of the solar system 4.567 Gyr ago similar to the situation of the pillars in M16 nowadays, where molecular cloud cores adjacent to an H II region will be hit by an SN explosion in the future. We show that the triggered collapse and formation of the solar system as well as the required enrichment with radioactive 26Al? are possible in this scenario.