Exit Big Bang? The Universe Is Anisotropic!

Of few things truly certain we are, but of many things most falsely speak…

Astronomers assumed for decades, without any proof, that the Universe was expanding at the same rate in all directions: it was simpler that way (after all some hanger-ons were claiming they were present during the “First Three Minutes”!… and thus became very famous…). A new study based on data from ESA’s XMM-Newton, NASA’s Chandra and the German-led ROSAT X-ray observatories suggests this key premise of cosmology might be wrong.

The Universe in simplified glory. However… Not as simple as expected! The blue areas expand more slowly than expected, the yellow areas faster. In isotropy, the image would be monochromatic red. Credit: © Konstantinos Nikolaos Migkas, Uni Bonn/Astronomy & Astrophysics. And the differences are not small: thirty percent! (30%!)

The isotropy hypothesis says that the Universe has, despite some local differences, the same properties in each direction on the large scale. The hypothesis has been supported by observations of the cosmic microwave background (CMB). An alleged direct remnant of the Big Bang, the CMB would reflect the state of the Universe as it was in its infancy, at only 380 000 years of age. The CMB’s uniform distribution in the sky suggested that in those early days the Universe must have been expanding at the same rate in all directions.

If this would still be true in more recent times, the speed of galactic clusters should average out. But significant differences were observed.

The astronomers used X-ray temperature measurements of the extremely hot gas that pervades the clusters and compared the data with how bright the clusters appear in the sky. Clusters of the same temperature and located at a similar distance should appear similarly bright. But that is not what the astronomers observed.

Clusters with the same properties, with similar temperatures, appeared to be less bright than expected in one direction of the sky, and brighter than expected in another direction. The difference was quite significant, around 30 percent. These differences are not random but have a clear pattern depending on the direction in which we observed in the sky.

Before challenging the widely accepted status quo ante, the cosmology model known as LCDM, which provides the basis for estimating the cluster distances, other possible explanations were looked at. Perhaps, there could be undetected gas or dust clouds obscuring the view and making clusters in a certain area appear dimmer. The data, however, do not support this scenario. Nor does it support that the distribution of clusters is affected by bulk flows, large-scale motions of matter caused by the gravitational pull of extremely massive structures such as large cluster groups.

The authors speculate that this uneven effect on cosmic expansion might be caused by Dark Energy, the mysterious component of the cosmos which accounts for the majority—around 69% – of its overall energy. Very little is known about dark energy today, except that it appears to have been accelerating the expansion of the Universe in the past few billion years.

Meanwhile, lots of things will have to be recomputed… And the flow of surprises from heavens doesn’t stop here… A Milky way sized Dark Matter galaxy would have been discovered…

Patrice Ayme

Tags: Big Bang, Universe Anisotropy