Astronomy

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

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A

AA

L

AA

LLLLI

G

II

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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