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Bjarne- Super Nova
Triggered Star Formation Inside the Shell of a Wolf-Rayet Bubble as the origin of the Solar System
ABSTRACT: A critical constraint on solar system formation is the high 26Al/27Al abundance ratio of 5 × 10-5 at the time of formation, which was about 17 times higher than the average Galactic ratio, while the 60Fe/56Fe value was about 2 × 10-8, lower than the Galactic value. This challenges the assumption that a nearby supernova was responsible for the injection of these short-lived radionuclides into the early solar system. We show that this conundrum can be resolved if the Solar System was formed by triggered star formation at the edge of a Wolf-Rayet (W-R) bubble. Aluminium-26 is produced during the evolution of the massive star, released in the wind during the W-R phase, and condenses into dust grains that are seen around W-R stars. The dust grains survive passage through the reverse shock and the low density shocked wind, reach the dense shell swept-up by the bubble, detach from the decelerated wind and are injected into the shell. Some portions of this shell subsequently collapses to form the dense cores that give rise to solar-type systems. The subsequent aspherical supernova does not inject appreciable amounts of 60Fe into the proto-solar-system, thus accounting for the observed low abundance of 60Fe. We discuss the details of various processes within the model and conclude that it is a viable model that can explain the initial abundances of 26Al and 60Fe. We estimate that 1-16% of all Sun-like stars could have formed in such a setting of triggered star formation in the shell of a WR bubble.
Bjarne- Super Nova
Aluminum-26 and Asteroid Heating
26Al was present when meteorites were forming. It is a radioactive isotope with a half-life of only 700 thousand years, so its presence means that the solar system formed within a few half-lives of the formation of 26Al in an exploding star. It decayed by emitting a beta particle (an electron), creating 26Mg (magnesium-26) and releasing energy. The energy released is considerable. If 26Al made up only 5 x 10-5 (0.005%) of all the aluminum in a chondrite (most is aluminum-27, which is not radioactive), it would release enough energy to melt asteroids a few kilometers across and larger. Lower amounts of 26Al cause less melting.
Because aluminum was probably distributed uniformly throughout the asteroid, the body would have been heated uniformly, except for a temperature gradient in the regions near the surface where heat radiated into space. Once 26Al had decayed for five or ten half-lives it was not abundant enough to heat an asteroid, so continuous cooling began.
Bjarne- Super Nova
Jernmeteoritterne menes dannel ved sammenstød mellem to asteroider, hvor i det mindste den ene har haft en størknet jernkerne, som er blevet afkølet meget langsomt. Energien, som har opvarmet asteroiden, så flydende jern kunne synke mod centrum, stammer fra radioaktivt henfald af 26Al. Det har været den sædvanlige opfattelse, at den nødvendige 26Al stammer fra en supernove, som eksploderede kort tid før Solsystemet blev dannet. Man har antaget, at den var selve årsagen til kollaps af den molekylsky, der kort tid efter blev til Solsystemet. Problemet ved denne hypotese er, at forholdet 26Al/27Al målt i Solsystemet er 17 gange større end Mælkevejens gennemsnit, hvorimod isotopforholdet 60Fe/56Fe for jern er mindre end Mælkevejens gennemsnit. Det har hidtil været en gåde, hvordan en supernova kan producere så meget 26Al uden samtidigt at producere 60Fe. Den nye hypotese antager, at 27Al tabes til omgivelserne via en kraftig stjernevind fra en Wolf-Rayet stjerne, som hurtigt udvikler sig til en asymmetrisk core-collaps supernova, som ikke producerer store mængder 60Fe.
Forfatterne anslår, at mellem 1% og 16% af sollignende stjerner kan være dannet i en WR-boble. Man kan kombinere disse procenter med artiklen om en månes stabiliserende indflydelse på en exoplanets klima til at konkludere, at Jorden sandsynligvis ikke er så gennemsnitlig, som man undertiden antager.
- Emnet 'Blev Solsystemet dannet på randen af en Wolf-Rayet boble' er lukket for nye svar.