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Solving Two 30-year Mysteries in the Formation and Dynamical Evolution of Binary Stars

Most stars are born in binary and multiple systems. Nearly all very close binaries with orbital periods P < 5 days are in triples, initially suggesting that the tertiary companion played a role in the dynamical hardening of the inner binary. However, several properties of these hierarchical triples are inconsistent with dynamical models. I will share how recent observations coupled to population synthesis models resolve this apparent discrepancy. The second mystery involves binaries across intermediate separations a = 10 – 100 AU. Early adaptive optics surveys discovered a substantial excess of these binaries in low-density star-forming regions like Taurus and Upper Scorpius compared to the galactic field population. Field stars represent an ensemble average of different star-forming environments, and thus it was predicted that dense star-forming regions must preferentially disrupt intermediate-period binaries in order to compensate for the observed excess in low-density environments. However, recent observations have shown that even the dense Orion Nebula Cluster manifests a similar or even larger binary fraction across intermediate separations compared to the field. I will demonstrate how an overlooked selection bias fundamentally alters the inferred primordial binary period distribution, yielding significant implications for star formation and the initial mass function.


Cody Hall

Prof. Max Moe, University of Wyoming

December 06, 2023
2:00pm - 3:00pm