Physics

Parts of the universe may be expanding faster than others

Parts of the universe may be e...
Different parts of the universe may be expanding at different rates, according to new observations
Different parts of the universe may be expanding at different rates, according to new observations
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Different parts of the universe may be expanding at different rates, according to new observations
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Different parts of the universe may be expanding at different rates, according to new observations
In this new X-ray map, yellow regions of space are expanding fastest, while purple areas are expanding slower
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In this new X-ray map, yellow regions of space are expanding fastest, while purple areas are expanding slower

One of the core components of cosmology is the understanding that the universe is expanding evenly in all directions. It was predicted by theory decades ago, and supported by measurements of the cosmic microwave background. But new X-ray observations now suggest that this may not be the case after all – certain areas may be expanding faster than others.

The isotropy hypothesis says that the universe has more or less the same properties in any direction. That’s true on the absolutely gigantic scale of the cosmos, anyway – there are obviously differences at the local scale.

This idea has been a lynchpin of cosmology for decades, and recent observations have agreed with it. 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. And as predicted, it was “almost perfect,” with only tiny temperature variations in different directions.

But looking at the CMB is looking at the universe when it was a cosmic newborn, merely 380,000 years old. Fast-forward 13.5 billion years, and there’s no guarantee the universe is still so uniform today. That’s exactly what the new study set out to investigate – and the results surprised the researchers.

“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. “If the isotropy hypothesis was correct, the properties of the clusters would be uniform across the sky. But we actually saw significant differences.”

In this new X-ray map, yellow regions of space are expanding fastest, while purple areas are expanding slower
In this new X-ray map, yellow regions of space are expanding fastest, while purple areas are expanding slower

The team made these observations using a range of X-ray observatories, including ESA’s XMM-Newton, NASA’s Chandra and Germany’s ROSAT. 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.

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. But to their surprise, the researchers noticed that this wasn’t the case.

“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. “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.”

The team ruled out other factors that might influence the results. The data didn’t support the idea that dust and gas clouds were making certain areas fainter, nor the idea that the enormous gravitational effects of the clusters were affecting the measurements. That leaves the team with the answer that different parts of the universe are expanding at different rates.

The implications of this are huge. Many astronomical measurements are based on the fundamental assumption that certain cosmological parameters are constant across the entire universe, so there’s no telling what else we’re wrong about.

“If the universe is truly anisotropic, even if only in the past few billion years, that would mean a huge paradigm shift because the direction of every object would have to be taken into account when we analyze their properties,” says Migkas. “For example, today, we estimate the distance of very distant objects in the universe by applying a set of cosmological parameters and equations. We believe that these parameters are the same everywhere. But if our conclusions are right than that would not be the case and we would have to revisit all our previous conclusions.”

Thankfully, the researchers don’t recommend a hasty return to the drawing board. They admit that the sample is relatively small, and more data is needed before such profound conclusions can be accepted. Future X-ray missions, such as ESA’s Euclid, will provide that extra data.

The research was published in the journal Astronomy & Astrophysics. The team describes the work in the video below.

The Universe might not be expanding at the same rate everywhere

Source: ESA

6 comments
Jose Gros
One explanation for the difference in shift to red or other markers of 'expansion' may be we are in the middle of regions having different distances from us, nearest regions will have light arriving us sooner, thus, it corresponds to later times, while those very far away emit light arriving us from earlier days of universe, when speed of expansion was faster than today, also, if the speed of a cluster is faster or slower relative to us, this will influence, by Doppler effect, the features of light and any radiation arriving here, what is used to estimate the speed of universe expansion.
If optical phenomena could have a role, density of matter, thus, light refraction, not being uniform across the universe, is something I don't know. Blessings +
Nala
Holy crap, the repercussions of this discovery!!
buzzclick
>leaves the team with the answer that different parts of the universe are expanding at different rates< Why is it so difficult to conceive the universe as a breathing, constantly fluxing and flowing enormous entity, like our oceans. To conclude that it's always expanding doesn't make cosmological sense. And yes, I'm not an astrophysicist.
Cryptonoetic
This is a huge violation of the Cosmological Principle. Great work. Instant Nobel prize.
Nobody
I have always thought the Big Bang was nonsense since there are so many (black) holes in the theory that they needed inflation, imaginary dark matter and dark energy to prop it up. We are observing something where nothing is any longer where it was or possibly doesn't even exist anymore over a period of time so vast that even light has been gravity lensed or changed by the refractive indexes of the gasses in it. If there was a big bang my personal theory is that the universe is more to the order of 50-100 billion years old with at least seven or more generations of stars. If the smaller stars never went nova in each generation, they would still have mass but be simply cold dark cinders.(Dark matter) If this occurred to 20% of each generation of stars after seven generations there would only be about 10% still emitting visible light with many of the later generations looking like brown dwarf stars as they cooled. This longer timeline also allows more time for the stars generate heavier elements and to move apart without the need for the unprovable expansion theory. I also think that the bulk of the mass of the universe is beyond what we can observe and could explain why we are moving as we are. My favorite theory is that there are at least three universes occupying the same space with the mass and influence of each being felt by the others. Just like the idea that the id, ego and super ego all coexist in our minds, we have hell, our present state and heaven all right here. This is not here because of the big bang. These dimensions are here because of the Creator.
Bill Kurtz
I have been waiting for someone to do this study ever since learning that the data used to show the expansion of the universe speeding up, was taken from a small sample pointing to the same general direction. I hope that this study sampled galaxy’s in all directions. Remember, the expansion differentials are relative to our earth speeding through space.