46 ASTRONOMY • MAY 2018
O
ne of the most striking features
of the distribution of matter in
the universe is its filamentary
appearance, with long, luminous
strands of galaxies woven togeth-
er into a vast cosmic web.
Nowhere is this more evident than the
Perseus-Pisces Supercluster. This colossal chain
of galaxies snakes across more than 50° of the
northern sky, fed by a network of smaller fila-
ments that resemble tributaries f lowing into a
river. Embedded within these filaments are
densely populated groups and clusters of galaxies.
Between them lie immense voids.
Our own Milky Way Galaxy resides in the
outskirts of a similar structure known as the
Laniakea Supercluster. (Laniakea means “immea-
surable heaven” in Hawaiian.) Home to an esti-
mated 100,000 galaxies, it’s a tangled knot of
The matter in our universe forms
filaments and threads like a grand
cosmic web, tugging galaxies and
clusters into place along the way.
by Michael West
WHY DO
GALAXIES
A
L
I
G
N
?
A
AA
L
AA
LLLLI
G
II
GGGGN
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The galaxy cluster
MACS J0416.1–2403
is highly elongated.
The orientations of
its brightest member
galaxies, which appear
round and yellow in
this image, reflect this
arrangement. ESA/HUBBLE,
NASA, AND HST FRONTIER FIELDS