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
directions as gravity shepherds material along
filaments. This imprints a built-in memory of
their environment on these cannibals, one that
reflects 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
GARGANTUAN
GALAXIES
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.
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
traced by galaxies and clusters, but also reflected
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 influenced 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.
W W W.ASTR ONOMY.COM
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