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arXiv · 2203.15156

Constraining Black Hole Natal Kicks with Astrometric Microlensing

Jeff J. Andrews·Vicky Kalogera
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Abstract

Multiple pieces of evidence suggest that neutron stars receive large kicks when formed from the remnant of a collapsing star. However, the evidence for whether black holes (BH) receive natal kicks is less clear, reliant on weak constraints from the analysis of BH X-ray binaries and massive runaway and walkaway stars. Here we show for the first time that recent microlensing detections offer a new method for measuring the kicks BHs receive at birth. When a BH is identified through both photometric and astrometric microlensing and when the lensed star has a known distance and proper motion, the mass, distance and proper motion of the BH can be determined. We study the runaway velocities for components of eccentric binaries disrupted during a supernova, finding the peculiar velocity correlates strongly with the kick a BH received a birth, typically within 20\%, even when the natal kick is smaller than the orbital velocity. Therefore, by measuring the peculiar velocity of a BH or other compact object that formed from a binary that disrupted during core collapse, we are in effect measuring the natal kick that object received. We focus on MOA-2011-BLG-191/OGLE-2011-BLG-0462, an isolated, single BH detected by microlensing and consider a range of possible formation scenarios, including its formation from the disruption of a binary during a supernova event. We determine that MOA-2011-BLG-191/OGLE-2011-BLG-0462 has a Milky Way orbit consistent with a thick disk population, but if it were formed within the kinematic thin disk it received a natal kick $\lesssim$100 km s$^{-1}$.

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Jeff J. Andrews, Vicky Kalogera. 2022-03-29. Constraining Black Hole Natal Kicks with Astrometric Microlensing. https://doi.org/10.3847/1538-4357%2Fac66d6

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