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*SPACE DAILY
STELLAR CHEMISTRY
Cosmological Data Affected By An Unexpected Source Of Radiation In
Interstellar Space
Dr. Gerrit Verschuur, a pioneer in the science of radio astronomy, has
been studying the properties of the Milky Way using interstellar HI for
almost 50 years. According to his recent work, it appears that many of
the small-scale structures observed by WMAP are correlated with HI.
by Staff Writers
Memphis TN (SPX) Nov 13, 2007
The widely lauded discovery of small-scale structure in the cosmic
microwave background may be seriously affected by a previously
unidentified source of radio emission in our own Milky Way Galaxy <#>.
This is the conclusion arrived at by Dr. Gerrit Verschuur, Adjunct
Professor of Physics at the University of Memphis. His work will be
published in the December 10 issue of the Astrophysical Journal.
Verschuur was studying data from the first ever all-sky survey of
interstellar neutral hydrogen (HI) when he noticed intriguing
similarities to the structure observed by the Microwave Anisotropy Probe
<#> (WMAP) spacecraft.
WMAP was designed to detect faint variations in the cosmic microwave
background, a pervasive signal left over from the Big Bang itself. This
anisotropy may represent the first step in the structural evolution of
the universe, a middle ground between the ultra-smooth cosmic microwave
background and the clusters of galaxies <#> that exist today.
The anisotropy detected with WMAP confirms a discovery made a decade
earlier by the Cosmic Background Explorer (COBE) spacecraft. As a
result, the COBE scientists won the 2006 Nobel Prize in Physics.
However, if even a small fraction of the anisotropy can be associated
with structure in the Milky Way, the cosmological interpretations of the
data could be called into question.
Verschuur, a pioneer in the science <#> of radio astronomy, has been
studying the properties of the Milky Way using interstellar HI for
almost 50 years. According to his recent work, it appears that many of
the small-scale structures observed by WMAP are correlated with HI.
To describe Verschuur's discovery as controversial would be an
understatement. "I realize that my results may not be readily accepted
by traditional cosmologists," Verschuur says, "but I hope they will at
least consider the possibility that their data may have been compromised
by what appears to be a previously unidentified source of weak radio
emission originating from our own Galaxy."
Verschuur points out that the WMAP researchers went to enormous lengths
to remove contributions from known physical processes occurring in the
Milky Way, but the WMAP signals associated with the HI may result from a
previously unidentified process. "No one could have foreseen the
existence of this newly discovered relationship," Verschuur continues.
"After all, a comprehensive HI survey for the northern sky was only
completed in 1997 and the all-sky version became widely available even
more recently, in 2005."
It will be challenging for cosmologists to prove that the weak radio
signals detected by WMAP are not originating from the Milky Way.
Verschuur points out that a more fruitful approach may be to determine
whether or not something new can be learned about the physics of
interstellar HI structure by considering examples of the close
associations between HI and the anisotropy observed by WMAP.
As a student of interstellar HI, Verschuur is excited by his new
discovery. "I now treat the WMAP peaks as markers that indicate where to
focus my efforts," he says.
Further study of the relationships between HI and small-scale structure
observed by WMAP will surely reveal a host of new information about the
physics and dynamics of our own Milky Way Galaxy <#>.
The new discovery, if confirmed, means that the structure superimposed
on the cosmic microwave background is produced in the Milky Way and does
not have a cosmic origin. Thus the cosmic microwave background signal
from the early universe may be smoother than anyone expected, which
raises new questions as to how structure ever emerged in the universe to
create galaxies.
Verschuur holds out the hope that bright young theorists will tackle
this problem and that some members of a new generation of radio
astronomers will focus on the Milky Way to study interstellar HI using
the WMAP signals to target their research.
The first inkling that a Milky Way component was still present in the
WMAP all-sky image came while Verschuur was preparing illustrations for
his new book on radio astronomy, The Invisible Universe, published in
early 2007. He had available a color print of the all-sky image of the
WMAP data and another of the HI data (integrated over all velocities <#>
frpm 450 to 400 km/s) to the same scale.
He couldn't help noticing intriguing similarities between structures in
the two maps. That seemed to merit a closer look. At the time he had
been working with the HI data as part of an unrelated project and had
available HI maps at dozens of velocities that could quickly compared to
details in the WMAP structure. Note that due to motion of the gas in
space, the HI emission is observed over a wide range of velocities
introduced by the Doppler effect, which shifts the observed frequency of
the HI emission by slight amounts.
The WMAP data were subsequently made available to him by Wayne Landsman
and Gary Hinshaw of the WMAP team based at the Goddard Space Flight Center.
Verschuur has produced over 1,000 maps of HI structure in small areas of
sky for comparison with the WMAP data. "These comparisons reveal
hundreds of close associations between HI and WMAP features and it will
take years to fully report this work. This field is wide open for others
to get involved.