A Globular Cluster Toward M87 with a Radial Velocity < -1000 km/s: The
  First Hypervelocity Cluster
  We report the discovery of an object near M87 in the Virgo Cluster with an
extraordinary blueshift of -1025 km/s, offset from the systemic velocity by
>2300 km/s. Evaluation of photometric and spectroscopic data provides strong
evidence that this object is a distant massive globular cluster, which we call
HVGC-1 in analogy to Galactic hypervelocity stars. We consider but disfavor
more exotic interpretations, such as a system of stars bound to a recoiling
black hole. The odds of observing an outlier as extreme as HVGC-1 in a
virialized distribution of intracluster objects are small; it appears more
likely that the cluster was (or is being) ejected from Virgo following a
three-body interaction. The nature of the interaction is unclear, and could
involve either a subhalo or a binary supermassive black hole at the center of
M87.
