The Runaway Binary LP 400-22 is Leaving the Galaxy

TL;DR

LP 400-22 is a distant, high-velocity binary white dwarf system unbound to the Galaxy, likely originating from dynamical interactions in globular clusters rather than supernovae or the Galactic center.

Contribution

This study refines the orbital parameters and distance of LP 400-22, providing new insights into its origin and ruling out previous hypotheses such as supernova ejection.

Findings

LP 400-22 has a tangential velocity over 830 km/s, unbound to the Galaxy.

The system is a double white dwarf with no detectable pulsar companion.

Its orbit suggests a possible origin in globular clusters, not the Galactic center.

Abstract

We present optical spectroscopy, astrometry, radio, and X-ray observations of the runaway binary LP 400-22. We refine the orbital parameters of the system based on our new radial velocity observations. Our parallax data indicate that LP 400-22 is significantly more distant (3 sigma lower limit of 840 pc) than initially predicted. LP 400-22 has a tangential velocity in excess of 830 km/s; it is unbound to the Galaxy. Our radio and X-ray observations fail to detect a recycled millisecond pulsar companion, indicating that LP 400-22 is a double white dwarf system. This essentially rules out a supernova runaway ejection mechanism. Based on its orbit, a Galactic center origin is also unlikely. However, its orbit intersects the locations of several globular clusters; dynamical interactions between LP 400-22 and other binary stars or a central black hole in a dense cluster could explain the origin of this unusual binary.