Free Astronomy Magazine March-April 2018

24 MARCH-APRIL 2018 SOLAR SYSTEM helped to disperse the cluster relatively quickly, and the Sun continued alone its path around the centre of the galaxy. That the explosion of a supernova really triggered the birth of the Solar System is not an established truth. Indeed, though that mechanism is effective in destabilizing a cloud of interstellar material, and it is cer- tainly the most widespread mechanism in our galaxy, it is not the only blueprint for powering the formation of new stars. Moreover, in the specific case of our Solar System, a birth due to a supernova is ques- tionable because of a specific peculiarity: the anomalous initial abundance of two specific radioisotopes, aluminium-26 ( 26 Al) and iron-60 ( 60 Fe). These two elements are widespread in the galaxy in constant aver- age ratios with respect to their stable forms, 27 Al and 56 Fe, and supernova explo- sions are helpful in keeping the ratios con- stant, as they pour these radioisotopes, along with many other elements, into in- terstellar space. These elements, generi- cally called ‘metals’, end up enriching the hydrogen clouds that are mainly scattered in the galactic disk. Whenever new stars and planetary systems form under the im- pulse of a supernova, in a cloud enriched with metals, they inherit from the interstel- lar medium the 26 Al/ 27 Al and 60 Fe/ 56 Fe ratios typical of the galaxy. When the two radioisotopes combine with other elements to form complex structures, in that specific scenario the ratios with re- spect to the stable isotopes begin to change due to their decay, ending in the complete disappearance of the radioiso- topes. Aluminium-26 has a half-life of about 700,000 years, while iron-60 has a half-life of about 1.5 million years. There- fore, the only way we have to verify their presence and their abundances at the Solar System’s time zero is by studying the iso- topic variations in their decay products. Meteorites are the ideal subjects on which T his image of part of the Carina Nebula shows in its centre a Wolf-Rayet star (WR 22) whose powerful winds are thinning the gases that surround it, up to more than 2 par- secs away. In some cases, WRs can sweep re- gions of space larger than 10 parsecs. [ESO]