The team ruled out other factors that might influence the results. These differences are not random but have a clear pattern depending on the direction in which we observed in the sky.” “The difference was quite significant, around 30 percent. “We saw that clusters with the same properties, with similar temperatures, appeared to be less bright than what we would expect in one direction of the sky, and brighter than expected in another direction,” says Thomas Reiprich, co-lead author of the study. But to their surprise, the researchers noticed that this wasn’t the case. If the universe was the same in all directions – and was expanding at the same rate everywhere – then clusters that were around the same temperature and distance should have a similar brightness.
This allowed them to take the temperature of the hot gas in those galaxy clusters, and compare the results to how bright those objects are in the sky. The team made these observations using a range of X-ray observatories, including ESA’s XMM-Newton, NASA’s Chandra and Germany’s ROSAT. But we actually saw significant differences.” “If the isotropy hypothesis was correct, the properties of the clusters would be uniform across the sky. “Together with colleagues from the University of Bonn and Harvard University, we looked at the behavior of over 800 galaxy clusters in the present universe,” says Konstantinos Migkas, co-lead author of the study. That’s exactly what the new study set out to investigate – and the results surprised the researchers. Fast-forward 13.5 billion years, and there’s no guarantee the universe is still so uniform today. And as predicted, it was “almost perfect,” with only tiny temperature variations in different directions.īut looking at the CMB is looking at the universe when it was a cosmic newborn, merely 380,000 years old. In 2013, ESA unveiled a map made by the Planck space telescope of the cosmic microwave background (CMB), radiation left over from the Big Bang. This idea has been a lynchpin of cosmology for decades, and recent observations have agreed with it. That’s true on the absolutely gigantic scale of the cosmos, anyway – there are obviously differences at the local scale. The isotropy hypothesis says that the universe has more or less the same properties in any direction. But new X-ray observations now suggest that this may not be the case after all – certain areas may be expanding faster than others. It was predicted by theory decades ago, and supported by measurements of the cosmic microwave background.
One of the core components of cosmology is the understanding that the universe is expanding evenly in all directions.
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