Short lived radionuclides ( SLRs ) like ^ { 26 } Al are synthesized by massive stars and are a byproduct of star formation .
The abundances of SLRs in the gas of a star-forming galaxy are inversely proportional to the gas consumption time .
The rapid evolution of specific star formation rate ( SSFR ) of normal galaxies implies they had mean SLR abundances \sim 3 – 10 times higher at z = 2 .
During the epoch of Solar system formation , the background SLR abundances of the Galaxy were up to twice as high as at present , if SLR yields from massive stars do not depend on metallicity .
If SLRs are homogenized in the gas of galaxies , the high SSFRs of normal galaxies can partly explain the elevated abundance of SLRs like ^ { 60 } Fe and ^ { 26 } Al in the early Solar system .
Starburst galaxies have much higher SSFRs still , and have enormous mean abundances of ^ { 26 } Al ( ^ { 26 } Al/ ^ { 27 } Al \approx 10 ^ { -3 } for Solar metallicity gas ) .
The main uncertainty is whether the SLRs are mixed with the star-forming molecular gas : they could be trapped in hot gas and decay before entering the colder phases , or be blown out by starburst winds .
I consider how variability in star-formation rate affects the SLR abundances , and I discuss how SLR transport may differ in these galaxies .
The enhanced ^ { 26 } Al of starbursts might maintain moderate ionization rates ( 10 ^ { -18 } – 10 ^ { -17 } \sec ^ { -1 } ) , possibly dominating ionization in dense clouds not penetrated by cosmic rays .
Similar ionization rates would be maintained in protoplanetary discs of starbursts , if the SLRs are well-mixed , and the radiogenic heating of planetesimals would likewise be much higher .
In this way , galaxy evolution can affect the geological history of planetary systems .