“ If I can borrow a line from the diamond people,
herpes is forever. ” — STEVEN TRIEZENBERG, PAGE 10
In the News
Atom & Cosmos Ice cubes in space
Genes & Cells Genes behind migration
Life Chicks count after they hatch
STORY ONE
Heavyweights
spotted in the
early universe
Newfound massive galaxies
may force theorists to revisit
leading formation model
By Ron Cowen
Pe
t
g
mering into the center of five of
he youngest known clusters of
alaxies in the universe, astrono-ers recently found several full-grown, cigar-chomping adults among the
myriad of toddlers. The remote galaxies
hail from a time when the 13.7-billion-
year-old cosmos was less than 5 billion
years old. Yet measurements reveal that
the bodies are just as massive as galaxies
like the modern-day Milky Way, which
took at least 10 billion years to mature.
C. COLLINS ET AL./NATURE
The findings appear to call into question the leading theory of galaxy formation, known as the dark matter model,
at least as it applies to the dense regions
where galaxies congregate into clusters,
says Chris Collins of the Liverpool John
Moores University in England. He and his
colleagues used the infrared Subaru telescope atop Hawaii’s Mauna Kea to observe
the galaxies, and the team describes the
findings in the April 2 Nature.
“No doubt the theorists will want to say
that tweaking [the model] in very dense
regions will suffice, but I think the problem could be more general than that,”
Collins says.
The highly successful model holds that
the gravity of a proposed, invisible material known as cold dark matter draws
together gas and stars to form galaxies.
Because of dark matter’s properties, the
model always builds tiny, lightweight
galaxies first, merging these small-fry to
make bigger bodies. Indeed, simulations
suggest that having formed in the young
universe, the galaxies the team examined
should have attained only about 20 percent of the weight actually observed.
In the dense environment of a cluster,
galaxy formation is predicted to occur
more quickly. Nonetheless, there doesn’t
seem to have been enough time, some
4 billion to 5 billion years after the Big
Bang, for the five massive galaxies to have
formed by the merging of smaller galaxies, according to the model. The findings suggest that some massive galaxies
formed wholesale, rather than cannibal-
This infrared image shows a remote
cluster with a galaxy (arrow) about five
times more massive than simulations
suggest it should have been when the
universe was one-third its current age.
izing their neighbors to build up stars and
gas little by little.
“These observations are certainly surprising,” comments theorist Gus Evrard
of the University of Michigan in Ann
Arbor. Although more data and even
larger-scale simulations are needed to
determine whether the observations and
theory are truly inconsistent, “the difference between nature’s brightest cluster galaxies and the simulated sample is
quite striking,” he says.
Evrard collaborates on the Millennium
Simulation, an international effort that
combines the largest supercomputer
simulation of the growth of dark matter
ever attempted with new techniques for
tracking the evolution of the visible universe. Collins’ team directly compared its
observations of the five galaxies with the
