Astronomy

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directions as gravity shepherds material along
filaments. This imprints a built-in memory of
their environment on these cannibals, one that
ref lects the surrounding cosmic web. In a
sense, giant galaxies are like spiders waiting for
prey, only it is smaller galaxies rather than bugs
that they devour, and the web they sit in is
elongated rather than circular.
Alternatively, given enough time, gravity’s
relentless tug will slowly reorient galaxies until
they align with their surroundings. Theoretical
calculations and computer simulations suggest
this should occur on timescales shorter than
the age of the universe, which means that even
if a galaxy was initially misaligned with its
surroundings, it should have fallen into line
by today.
As is often the case in science, it’s possible,
even likely, that there’s more than one explana-
tion for galaxy alignments, with mergers along
filaments and twisting due to gravitational
effects both contributing to the end result.

Is there more to
cosmic congruence?
“Things are the way they are because they were
the way they were,” maverick astronomer Fred
Hoyle once quipped.
Beginning with the thinnest of strands —
tiny irregularities in the primordial distribution
of matter — gravity has slowly woven a cosmic
web of sublime beauty and complexity. It’s
astonishing to think that the filamentary distri-
bution of matter on large scales is not only

traced by galaxies and clusters, but also ref lected

in their orientations.

There’s tantalizing evidence that alignments

might even extend to other scales. In 2014, a

team led by Damien Hutsemékers from the

University of Liège in Belgium reported that the

spin axes of some quasars are parallel to each

other over distances of billions of light-years,

and that they share the same orientation as the

surrounding filamentary structure.

If confirmed, this would suggest that the

cosmic web has even inf luenced the supermas-

sive black holes powering quasars, further evi-

dence of a truly remarkable coherence of

structures in the universe.

Michael West is deputy director for science

at Lowell Observatory in Flagstaff, Arizona.

His most recent book is A Sky Wonderful With Stars:

50 Years of Modern Astronomy on Maunakea.

People come in a wide range of

shapes and sizes. According to

Guinness World Records, the heavi-

est person ever was an American

named Jon Brower Minnoch, who

tipped the scales at a whopping

1,400 pounds (635 kilograms). At

the other extreme, a Mexican

woman named Lucia Zarate, who

suffered from an extreme form of

dwarfism, weighed only 13 pounds

(6 kg) as an adult — less than

1 percent of Minnoch’s weight.

But that’s nothing compared

to galaxies, where the biggest

outweigh the smallest by factors

of a million or more. Lurking in the

centers of many galaxy clusters are

the largest known stellar systems

in the universe, giant elliptical

galaxies that could easily swallow

dozens of their neighbors — and

probably have. It may be no

coincidence that these behemoths

are so strongly aligned with their

surroundings. — M.W.

GARGANTUAN

GALAXIES

A computer simulation of our home galaxy,

the Milky Way. Today’s simulations are

more realistic than ever before, following

the birth and evolution of galaxies from

the Big Bang to the present day. This

simulation required 15 days of number

crunching with one of the world’s fastest

supercomputers. HOPKINS RESEARCH GROUP/CALTECH

MRC 1138-262, the Spiderweb Galaxy, is seen

in this Hubble Space Telescope image as it

appeared only 2 billion years after the Big Bang.

The giant galaxy, located at the center of a

growing cluster, is being assembled via mergers

of smaller systems of gas, dust, and stars. Such

mergers occur preferentially along directions

defined by the surrounding cosmic web. NASA, ESA,

G. MILEY, R. OVERZIER AND THE ACS SCIENCE TEAM