74 ASTRONOMY • DECEMBER 2018
Hunting for
cluster pairs
Hundreds of galaxies
populate the northeastern
corner of Canes Venatici
the Hunting Dogs. These
island universes make up
the massive galaxy cluster
Abell 1758, which lies
some 3.2 billion light-years
from Earth. About 20 years
ago, astronomers learned
that this throng consists of
two subclusters, separated
by 2.4 million light-years
yet still bound together by
gravity. But more recent
observations reveal that
the northern subcluster
seen in this Hubble Space
Telescope image also
splits into two segments.
Disturbances within these
sections suggest that they
formed as smaller clusters
collided and merged.
NASA/ESA/HUBBLEBREAK
THROUGH