March 15, 2005
Archaeological astronomers glimpse back in time and discover the most distant galaxy yet
By Ryan Anderson For the Daily
niversity research fellow Christopher Mullis and
his international team of astronomers are cosmic
archaeologists. Just as conventional archaeologists
dig through the accumulated sediment of hundreds and
thousands of years to uncover relics from long ago, his group
searches the skies for relics of a much younger universe.
Rather than shovels and picks, they travel back in time
using telescopes, and they dig much deeper. They recently
discovered an ancient object that pushes the limits of the
observational universe to only five billion years after the
The object that they found is a massive galaxy cluster nine-
billion light years away, the farthest ever observed. A light year
is the distance light travels in one year, meaning that light from
the cluster has been traveling across the vacuum of space for
two-thirds the lifetime ofthe universe. In making the discovery,
Mullis worked with astronomers from the European Southern
Observatory, the Max
Planck Institute for
This gas, Extraterrestrial Physics
and the Astronomical
heated Institute at Potsdam.
A galaxy cluster is
during cluster the name astronomers
foo is give to groups of gal-
formation, is axies that are trapped
what allowed together by their
the tEach galaxy is made of
hundreds of billions of
make their stars like the sun, and
there can be thousands
record- of galaxies in a clus-
ter. Galaxy clusters
breaking find. take billions of years
to coalesce from an
unstable assortment of
partially formed galaxies into a mature cluster. Clusters
interact with one another to form the largest structures in
"Clusters are often difficult to find based on visual obser-
vations," Mullis said. "However, they glow brightly in X-
ray light due to the hundred-million-degree gas that fills the
space between the galaxies."
This gas, heated during cluster formation, is what allowed
the team to make their record-breaking find.
The team used a complex computer program to search
through archived images from the XMM Newton X-ray satel-
lite and identify possible distant clusters. XMM-Newton was
launched in 1999 by the European Space Agency. Its wide
field of view and excellent light-gathering ability make it well
suited for detecting faint, distant objects. The cluster was dis-
GRAPHICS BY MATT DANIELS
LEFT: Nine billion light years spans the distance between the distant galaxy XMMU J2235 and Earth. RIGHT: Diagram of the distribution of galaxy clusters from Earth to XMMU J2235.
The number of galaxy clusters decreases the further the distance away from the Earth because the younger universe produces much larger clusters than the present-day universe.
covered in the background of an image of a black hole.
The cluster's X-ray signal is extraordinarily faint, Mullis
said. The entire signal from the galaxy cluster is made up
of a scant 280 photons, gathered during an exposure last-
ing 12.5 hours. As a comparison, on a sunny day, your eye
receives 10 quadrillion photons every second.
To measure the distance to the cluster, the team made opti-
cal observations from the ESO Very Large Telescope in South
America. By passing light through a spectrograph - an
instrument that separates the light from a source according to
wavelength, much like a prism - astronomers can tell what
chemical elements are present in the object they are observing.
Because the universe is constantly expanding, light that
leaves an object long ago gets stretched out during its journey.
Astronomers call this increase in wavelength "redshift." The
more redshifted an object is, the farther away it is. Using the
unique spectral fingerprints of certain elements to measure this
change, Mullis said the "eureka" moment came in late 2004,
when he analyzed the spectra from the cluster and determined
an astonishing distance of nine billion light years.
"We see an evolved cluster at five billion years (since the
Big Bang). That means it was forming at something like two
or three billion years," Mullis said. "The general expecta-
tion is that at higher distances clusters get more youthful, so
(this discovery) is particularly exciting."
Gus Evrard, a University professor of astronomy and phys-
ics, said fully developed clusters at this distance are expect-
ed from current theoretical models of the universe. "In that
respect, theory is actually ahead of observation," Evrard said.
There have been protoclusters found at distances still
greater than the cluster found by Mullis and his team. Those
objects, however, are not well-formed and lack the multi-mil-
lion-degree gas that characterizes a fully evolved cluster.
Evrard compared the situation to population density in
a sparsely populated state. There are bound to be counties
with a higher population than the surrounding area, but
those are not the same as a full-fledged city. Mullis and
his team have discovered the farthest and therefore most
ancient "city" of galaxies known.
"The finding of such a large cosmic structure at this age ...
is expected in a universe dominated by dark energy but not in a
universe dominated by dark matter," Evrard said. Dark matter is
the mysterious "missing mass" that cosmologists believe makes
up almost a quarter of the total mass/energy budget of our uni-
verse. The amount of dark matter in the universe determines the
structures that will form and how large they become.
By searching for the earliest formed clusters, astronomers
hope to get an estimate of the universe's dark matter content.
The current estimate is that dark matter makes up about one
quarter of the total mass/energy in the universe, Mullis said.
Dark energy is the energy contained in the vacuum of
space itself. It governs the rate of expansion of the universe.
Measuring the redshift of distant clusters helps cosmolo-
gists measure that expansion and get an estimate of the
dark energy content. Current estimates place dark energy
at three quarters of the total, Mullis said.
This amount of dark energy leads to the surprising con-
clusion that the universe is not only expanding, but acceler-
ating. Normal matter makes up only a small percent of the
total energy density. The vast majority of the universe is
made of matter and energy that we do not understand.
The discovery of such a distant cluster by analyzing
archived images from XMM-Newton was relatively easy,
Mullis said. This bodes well for the discovery of many more
super-distant galaxy clusters in the future, he added.
With a whole range of distant clusters to study, astrono-
mers will be able to infer the fundamental parameters of the
universe, and conclude how it evolved from the Big Bang to
the structures that we observe today.
'Super mice' may help strengthen bones
By Phil Svabik
Daily Staff Reporter
Move over Mickey, Minnie and even Mighty Mouse,
because while cartoonists have created mice able to
withstand falling anvils, researchers at the University
have engineered mice with a bone structure that even
the world's most famous mice might be envious of.
Molecular and Integrative Physiology Prof.
Ormond MacDougald and his fellow researchers
have recently been experimenting with mice that
have been genetically altered to produce less adi-
pocytes, or fat cells, and produce four times more
osteoblasts, or bone cells. Using these "super mice,"
researchers are on their way to better understand-
ing one possible mechanism for the development of
osteoporosis in older adults, which may also help
lead to a drug to treat the disease.
To produce the mice used in the study, an artifi-
cial sequence of DNA was injected into fertilized
mouse eggs, causing these genetically altered mice
to produce more of a certain signaling protein,
called WntlOb (pronounced Wint ten b) inside
their bone marrow. Signaling proteins regulate the
development of tissues in the body.
With higher levels of Wntl0b, the mice developed
stronger and larger bones than usual. There is a patent
pending on the genetically altered mice.
"There are many pharmaceutical companies that
are very actively developing very small molecules
or other approaches to activate this pathway with
the hope of providing a drug that could be used to
increase bone formation," MacDougald said.
"Most of the drugs that are out there just inhibit
the reabsorption of bone, and this would be a valu-
able tool within the tool kit that doctors have in
treating osteoporosis," he added.
Wntl0b is part of a family of 19 other Wnt signaling
proteins, which all help determine the type of cells that
bone marrow stem cells will become. These stem cells
can give rise to many different tissues such as bone, fat,
cartilage and connective tissue.
The Wntl~b signaling pathway can either block
the formation of undifferentiated cells to fat cells,
or encourage the production of bone cells, MacDou-
The findings from this study at the University will
help researchers better understand how osteoporosis
develops. Osteoporosis is a disease characterized by
a decrease in bone mass. Left untreated, it can lead
to a very high susceptibility to bone fractures and
breaks. The discovery that the WntlOb signaling
protein causes an increase in bone cell formation
helps researchers to better understand one mecha-
nism of bone formation and may possibly help lead
to drugs capable of regenerating lost bone mass.
The National Osteoporosis Foundation esti-
mates that 55 percent of Americans over the age
of 50 have osteoporosis, the vast majority of these
being women who can lose 20 percent of their bone
mass within a decade after menopause. As the baby
boomer generation continues to age, these figures
will likely increase, pushing the demand for medi-
cations to help prevent and cure the disease
However, Rackham student Christina Bennett,
researcher and first author of the WntlOb mice article,
which was published Feb. 21, hopes a drug might be
created as a result of the study, but does not necessarily
think the findings will lead directly to a cure-all drug.
"Wnt's are also involved in cancer so one of the
concerns would be if you stimulate Wnt signaling
you could also cause bone cancer," Bennett said,
though noting that cancer was not observed in any
of the mice involved in the study. She added that
in the development of a drug, a different protein or
other molecule aside from WntlOb that has the same
effect but would be safer could be used instead.
Previous research conducted by MacDougald and
other researchers last year showed that an excess of
WntlOb in fat cells of mice, instead of within the
bone marrow, causes the mice to have 50 percent
less body fat. This previous research on super skin-
ny mice, also could help researchers better under-
stand and treat obesity.
"This would be a valuable
tool within the tool kit that
doctors have in treating
- Ormond MacDougald
Molecular and Integra-
tive Physiology Prof.
Bennett is quick to point out that a decrease in
the fat cells as a side effect of a Wnt10b derived
drug to increase bone mass in osteoporosis patients
wouldn't necessarily be detrimental.
"But isn't that the perfect drug? I think a decrease
of fat in bone marrow or elsewhere wouldn't be a
negative thing," she said.
To quantitatively analyze the size and density
of the bones within the studied mice, the research
team utilized micro-computerized tomography, a
type of three-dimensional X-ray machine. Mac-
Dougald said the results showed that the bones
were stronger and larger and the mice were more
resistant to bone loss that occurs along with estro-
gen depletion, which is similar to post-menopaus-
al bone loss in women.
The researchers would not say exactly where
they plan to go from here, but they do want to
continue to study Wnt signaling and gain a better
understanding of precisely how Wnts, especially
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COURTESY OF ORMOND MACDOUGALD
X-rays of femur mice bones with different Wnt10b levels. The left bone has
increased Wnt10b protein levels causing a firmer bone development. The middle
has normal levels, and the right has a decrease of Wnt10b, resulting in fractures.
for more information call 734/998-6251
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