The distribution of N _ { * } , the number of OB stars per association or cluster , appears to follow a universal power-law form N _ { * } ^ { -2 } in the local Universe .
We evaluate the distribution of N _ { * } in the Small Magellanic Cloud using recent broadband optical and space-ultraviolet data , with special attention to the lowest values of N _ { * } .
We find that the power-law distribution in N _ { * } continues smoothly down to N _ { * } = 1 .
This strongly suggests that the formation of field massive stars is a continuous process with those in associations , and that the field stars do not originate from a different star formation mode .
Our results are consistent with the model that field massive stars represent the most massive members in groups of smaller stars , as expected if the clustering law applies to much lower masses as is expected from the stellar initial mass function ( IMF ) .
These results are consistent with the simultaneous existence of a universal IMF and a universal clustering law .
Jointly , these laws imply that the fraction of field OB stars typically ranges from about 35 % to 7 % for most astrophysical situations , with an inverse logarithmic dependence on the most populous cluster , and hence , on galaxy size and/or star formation rate .
There are important consequences for global feedback effects in galaxies : field stars should therefore contribute proportionately to the volume of the warm ionized medium , and equal relative contributions by superbubbles of all sizes to the interstellar porosity are expected .