Recent findings from Case Western Reserve University physicists and their collaborators may change cosmologists' understanding of when the oldest stars in our universe might have formed.
Glenn Starkman, Armington Professor of Physics and Astronomy at Case, and collaborators Craig Copi (Case), Dragan Huterer (then at Case, now Hubble Fellow at the University of Chicago), and Dominik Schwarz (then at CERN, now at the University of Bielfeld) have been studying cosmic microwave background (CMB) radiation—the afterglow radiation left over from the early ages of the universe.
The researchers published their study "Are the Low Notes of the Microwave Background Cosmic?" recently in the journal, Physical Review Letters.
The CMB has been called by some as the most conclusive piece of evidence of the Big Bang theory—the idea that the universe was created some 10 to 20 billion years ago in a hot and dense state and has been expanding and cooling since then.
The temperature of the CMB is extremely uniform all over the sky. However, tiny temperature variations or fluctuations (at the part per hundred thousand level) can offer great insight into the origin, evolution and content of the universe. These temperature variations were first seen in the early 1990's by instruments aboard the Cosmic Background Explorer (COBE) satellite. In the intervening years they have been studied over small portions of the sky by numerous ground and balloon-based experiments, but recently the Wilkinson Microwave Anistropy Probe produced a new all-sky map of the CMB.
Cosmologists express these temperature fluctuations as notes on a spherical drum. An all-sky map allows cosmologists to study the lowest notes of the CMB—the fluctuations over the largest angles.
One of the outstanding mysteries presented by the CMB—first noticed by COBE and now confirmed by WMAP—is that the lowest of these notes of the universe seem to be nearly missing.
Intriguingly, Starkman and colleagues have found that what little there is of these notes, seems to be rung by the solar system itself, and not by the early universe.
Back when our universe was only a mere 300,000 years old, it was much hotter and denser. At that point electrons were not bound to atoms, Starkman said. As the universe expanded and cooled, it went from an opaque, cloudy environment to the transparent one we see today. At that time, most of the photons in the universe were freed from the dense plasma and became free to travel through the expanding universe.
In the nearly 14 billion years since then, these photons have been stretched by the expanding universe so that instead of being photons of visible light, they are now microwaves, the so-called CMB. Yet, these photons still carry the imprints of the small differences in the temperature and density of their local environment—differences which later grew into the galaxies and clusters of galaxies we now seen in the universe, said Starkman.
These small differences were first measured in 1991 by instruments aboard the COBE satellite. This satellite produced the very first maps of the CMB.
With its improved technology, WMAP's map is of far higher resolution and quality, Starkman said. The properties of this map have excited the cosmology community over the last two years.
Now, a new analysis of the WMAP map of the CMB shows that patterns in the map align in unexpected ways with the shape of the solar system.
In 1991, researchers had noticed that data from the COBE satellite showed that the bass or very lowest notes in the universe were of very low intensity. Over the years, that information had mostly been forgotten, said Starkman. When WMAP provided more accurate maps of the microwave sky, the weakness of these bass notes was confirmed.
The "low note" fluctuations, according to Starkman, seem to be contaminated by a signal coming from the solar system itself or its neighborhood. In addition to changing our understanding of when the oldest stars in our universe may have formed, it could also challenge the standard "inflation" theory for the vast size and incredible smoothness of the universe and for the properties of the structures it contains, Starkman said.
The researchers decided to look beyond just the "volume" of each note. In their investigation, they assigned to each note (or for physicists, each multipole component of the CMB sky) a certain number of directions, called multipole vectors, with the lower notes having fewer directions.
"We found that the multipole vectors of the quadrupole and the octopole (the two lowest interesting groups of notes) were aligned in such a way that they knew about the ecliptic poles, which form the axis perpendicular to the plane of our solar system," reported Starkman. "They also seemed toknow about the solar system's motion through the universe."
"What is interesting to cosmologists is that the volume of the low notes was already unusually low. This suggests that, to the extent that we detect the low notes to begin with, much or all of what we see is not from the universe but from our own solar system," said Starkman. "This means the low notes of the universe are really missing—even more so than we thought they were."
New information about the low notes in the universe adds another conundrum to fundamental theories of the universe, said Starkman. In addition to the mysteries of dark matter and of the accelerating expansion of the universe, we must now add that whatever mechanism—inflation or something else—generated the structure we see in the universe, it knew not to make anything bigger than about the distance out to which we can see today. This might be because the universe is like a drum constrained by its shape only to produce certain notes. This would be important to explorations of the universe's topology, he said.
Alternately, it could be that what we are seeing is further evidence that we don't really understand gravity on the largest scales.
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