‘Where Are the Smallest Black Holes?’: Probing the mass gap with APOGEE
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The existence of the least massive black holes and most massive neutron stars are still debated, and with few objects identified between two to five solar masses, many believe in a “compact object mass gap”. Compact objects are dim and small, a consequence of being end of life stellar remnants. Therefore, our best chance to observe them is through influences on a close companion star in a binary system, where the objects orbit around a shared center of mass and can be detected by a radial velocity (RV) Doppler shift of the system’s spectral lines between observations. Using the Apache Point Observatory Galactic Evolution Experiment (APOGEE) we search for candidate host systems that have considerable evidence of binary interactions including RV variations, rapid rotation indicative of tidal interaction, and a single set of stellar spectral lines suggesting the secondary is compact. We find that only 0.7% of the APOGEE catalog possesses all these signatures, and we explore the 120 systems whose companion mass estimates are in the mass-gap regime. While previous efforts have identified individual systems, our work provides a more comprehensive search of a large sample that will help constrain the history and evolution of stellar-mass compact objects.