Big Bang echoes corrupted?Feb 03, 2004( taken from SpaceFlightNow ) |
In recent years, astronomers have obtained detailed measurements of the cosmic microwave background radiation - the 'echo' from the birth of the Universe during the Big Bang.
These results appear to indicate with remarkable precision that our Universeis dominated by mysterious 'cold dark matter' and 'dark energy'. But now agroup of UK astronomers has found evidence that the primordial microwave echoesmay have been modified or 'corrupted' on their 13 billion year journey to theEarth.
 Credit: University of Durham |
The team has found that nearby galaxy clusters appear to lie in regions ofsky where the microwave temperature is lower than average. This behaviour couldbe accounted for if the hot gas in the galaxy clusters has interacted with theBig Bang photons as they passed by and corrupted the information contained inthis echo of the primordial fireball. Russian physicists R. A. Sunyaev andYa. B. Zeldovich predicted such an effect in the early 1970's, shortly afterthe discovery of the cosmic microwave background radiation.
This Sunyaev-Zeldovich effect has previously been seen in the cases ofdetailed observations of the microwave background in the vicinity of a few richgalaxy clusters and the WMAP team themselves have reported seeing the effect intheir own data, close to cluster centres.
Now the Durham team has found evidence that hot gas in the clusters mayinfluence the microwave background maps out to a radius of nearly 1 degreefrom thegalaxy cluster centres, a much larger area than previously detected. Thissuggests that the positions of "clusters of clusters" or "superclusters" mayalso coincide with cooler spots in the pattern of microwave backgroundfluctuations.
"The photons in the microwave background radiation are scattered by electronsin nearby clusters," said Professor Shanks. "This causes important changes tothe radiation by the time it reaches us."
"If the galaxy clusters located several billion light years from Earth alsohave the same effect, then we must consider whether it is necessary to modifyour interpretation of the satellite maps of the microwave backgroundradiation."
If the Durham result is confirmed, then the consequences for cosmology couldbe highly significant. The signature for dark energy and dark matter lies inthe detailed structure of the ripples detected in the microwave background,tiny temperature variations that were created at a time when the radius of theUniverse was a thousand times smaller than it is today.
If this primordial pattern has been corrupted by processes taking place inthe recent past, long after galaxies and galaxy clusters formed, then it will,at best, complicate the interpretation of the microwave echo and, at worst,begin to undermine the previous evidence for both dark energy and cold darkmatter.
"The power of this wonderful WMAP data is that it indicates that interpretingthe microwave background 'echo' may be less straightforward than previouslythought," said team memberSir Arnold Wolfendale (previously Astronomer Royal).
The WMAP team has already reported that their measurements of the Big Bang'smicrowave echo may have been compromised by the process of galaxy formation atan intermediate stage in the Universe's history. They presented evidence thatgas heated by first-born stars, galaxies and quasars may have also corruptedthe microwave signal when the Universe was 10 or 20 times smaller than at thepresent day. Thus both the WMAP and Durham results suggest that the microwaveecho of the Big Bang may have had to come through many more obstacles on itsjourney to the Earth than had previously been thought, with consequent possibledistortion of the primordial signal.
"Our results may ultimately undermine the belief that the Universe isdominated by an elusive cold dark matter particle and the even moreenigmatic dark energy," said Professor Shanks.
Although the observational evidence for the standard model of cosmologyremains strong, the model does contain very uncomfortable aspects. These arisefirst because it is based on two pieces of "undiscovered physics" - cold darkmatter and dark energy - neither of which has been detected in the laboratory.Indeed, the introduction of these two new components greatly increases thecomplication of the standard Big Bang inflationary model.
The problems of dark energy run particularly deep: for example, its observeddensity is so small that it may be quantum mechanically unstable. It alsocreates problems for the theories of quantum gravity, which suggest that we maylive in a Universe with 10 or 11 dimensions, all of them shrunk, with theexceptions of three in space and one in time.
Many theorists would therefore like an escape route from today's standardmodel of cosmology and it remains to be seen how far these observationsdiscussedby the Durham group will go in this direction. But if correct, they suggestthat the rumours that we are living in a "New Era of Precision Cosmology" mayprove to be premature!
This release is based on the Paper, "Evidence for an ExtendedSunyaev-Zeldovich Effect in WMAP Data" by Adam Myers, Tom Shanks, PhilOutram, Bill Frith andSir Arnold Wolfendale (Dept. of Physics, University of Durham), to bepublished on 1 February 2004 in the Monthly Notices of the RoyalAstronomical Society 347, L67.
NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite was launched inJune 2001. It measures the minute temperature variations in the cosmicmicrowave background radiation over the full sky with unprecedented accuracy.
Cosmic microwave background (CMB) radiation is the radiant heat left overfrom the birth of the Universe during the Big Bang. Its properties contain awealth of information about physical conditions in the early Universe,more than13 billion years ago. The average temperature of the CMB today is minus 270.4degrees Celsius - only 2.73 degrees above absolute zero.
