CREATION BY STELLAR ABLATION OF THE LOW-MASS COMPANION TO PULSAR 1829-10

THE pulsar 1829 - 10 has a remarkable companion 1 of only approximately 10 Earth masses, which occupies a nearly circular orbit of 184-day period. Bailes et al. 1 speculate that this companion is a planet which has either survived the earlier stellar evolution and supernova which created the pulsar, or else formed through some sort of coagulation process during the lifetime of the pulsar. I argue here that another interpretation, which they excluded, may actually be more plausible: that the companion began its life as a star, and has been ablated down to its present mass by absorbing a portion of the pulsar's spindown energy. That similar phenomena have already been seen in two other binary pulsars, PSR 1957 + 20 (refs 2, 3) and PSR 1744 - 24A (refs 4, 5), lends preliminary credence to this suggestion. The (surprisingly small) final mass of the remnant is determined by the interplay between decreasing spindown luminosity, recession of the companion from the pulsar as a result of its mass loss, and, most importantly, shrinkage of the companion due to convective cooling of its interior.