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We consider the origins of enigmatic stellar populations in four Local Groupgalactic nuclei, specifically the Milky Way, M31, M32 and M33. These arecentrally concentrated blue stars, found in three out of the four nuclear starclusters (NSCs) considered here. Their origins are unknown, but could includeblue straggler (BS) stars, extended horizontal branch stars and young recentlyformed stars. Here, we calculate order-of-magnitude estimates for variouscollision rates, as a function of the host NSC environment and distance fromthe cluster centre. These rates are sufficiently high that BSs, formed viacollisions between main sequence (MS) stars, could contribute non-negligibly($\sim$ 1-10% in mass) to every surface brightness profile, with the exceptionof the Milky Way. Stellar evolution models show that the envelopes of red giantbranch (RGB) stars must be nearly completely stripped to significantly affecttheir photometric appearance, which requires multiple collisions. Hence, thecollision rates for individual RGB stars are only sufficiently high in theinner $\lesssim$ 0.1 pc of M31 and M32 for RGB destruction to occur. Collisionsbetween white dwarfs and MS stars, which should ablate the stars, could offer asteady and significant supply of gas in every NSC in our sample. The gas couldeither fragment to form new stars, or accrete onto old MS stars alreadypresent. Thus, collisional processes could contribute significantly to theobserved blue excesses in M31 and M33; future studies should be aimed at betterconstraining theoretical predictions to compliment existing and futureobservational data.

On the origins of enigmatic stellar populations in Local Group galactic nuclei