Free Astronomy Magazine March-April 2018

28 MARCH-APRIL 2018 SOLAR SYSTEM T his diagram shows the decay of 26 Al: a proton decays into a neutron, releasing a positron and a neu- trino as by-products; 26 Al is thus trans- formed into 26 Mg*, magnesium with higher energy than in its ground state; finally, the magne- sium is transformed into its stable form, 26 Mg, emitting a gamma photon with energy of 1.8 MeV, a frequency that in the galaxy is related to the pres- ence of the most mas- sive stars. [ESA] these, after an average journey of about ten parsecs, travelled in about 20,000 years, they reach the densest regions of the shell, where their speed slows to zero. Since the length of the journey is much shorter than the half-life of 26 Al, we can expect the average velocities of that iso- tope in the space dominated by WRs to be much lower than those of the stellar winds, which would demonstrate the ac- cumulation of the metal in the shell, and indeed this is the case. When, due to grav- itational instability, a part of the shell collapses into a centre of mass capable of spawning a new solar system, the system will con- tain more 26 Al than the galactic av- erage, but it will certainly not show an excess of 60 Fe, an element that remains in the WR’s core and that will not necessarily be re- leased if the star is instantly trans- formed into a black hole without going through the supernova phase. In conclusion, the Sun and our en- tire planetary system (including us) could be the offspring of a WR. Dwarkadas and his colleagues esti- mate that from 1% to 16% of all solar-type stars could be produced from those giant stars. V ikram V. Dwarkadas, Research Associate Professor in the Department of Astronomy and Astrophysics at the University of Chicago, is the first author of the new study proposing a WR star as a trigger for the birth of our Solar System. [The University of Chicago] presence of dust located a relatively short distance from the photosphere. That dust is made up of grains with sizes between about 0.3 and 2 microns, and the Dwarkadas team has shown that larger grains can overcome the severe environmental conditions that surround WRs, and can, therefore, reach the shell of the enormous bubble un- harmed. In the model proposed by the team, the 26 Al atoms launched into space are deposited on the dust grains they in- tercept along the way, and together with !