Surprise. The universe is expanding at different speeds in each direction

One of the basic cosmological assumptions is that the universe looks more or less the same in every direction if we look far enough. The latest research conducted with the help of the Chandra space observatories and XMM-Newton undermine this assumption.

Using data collected in the X-ray range, astronomers analyzed hundreds of galaxy clusters, the largest gravitational structures in the universe, and checked how their appearance changes depending on their location in the sky.

One of the pillars of cosmology - the field dealing with the history and fate of the entire universe - is that the universe is "isotropic", i.e. the same in all directions, "says Konstantinos Migkas of the University of Bonn in Germany. However, our work proves that there are several cracks in this pillar.

As a rule, astronomers agree that since the Big Bang the universe is constantly expanding. When you look at it, all objects in the universe move away from all others. If matter in the universe is more or less evenly distributed, all processes should be roughly the same in all directions. The latest results, however, indicate something else.

Based on our observations of galaxy clusters, we've found differences in the rate at which the universe is expanding, depending on which part of the universe we were looking at, '' says Gerrit Schellenberger of the Harvard Center for Astrophysics. This contradicts the most basic assumptions of cosmology.

Scientists have previously done a lot of research to determine if the universe is the same in every direction.

To this end, observations of exploding stars and infrared galaxies were used. Some of them indicated that the universe is isotropic, and some denied it.

However, the latest research used a strong, innovative and independent technique. It is based on the relationship between the temperature of the hot gas filling the galaxy cluster and the amount of x-ray radiation it emits. The higher the gas temperature in the cluster of galaxies, the brighter the galaxy should be in the X-ray range. After measuring the gas in the cluster, its brightness can be estimated in the X range. This method is therefore independent of cosmological values ​​such as the rate of expansion of the universe.

After estimating the x-ray brightness of the clusters in this way, the scientists calculated the level of brightness using another method that depends on cosmological values, including the rate at which the universe is expanding. In this way, scientists obtained visible velocities for the expansion of the universe for the entire sky. It turned out that in some directions the universe is moving away from us faster than in others.

After comparing the results with the results of other studies conducted by other research groups, which also pointed to the non-isotropic nature of the universe, it turned out that they agree on the direction in which the universe is expanding most slowly.

The authors of the new study concluded that there are two possible explanations for the results obtained.

One of them indicates that large groups of galaxy clusters can move together and not because of the expansion of the universe. It is possible, for example, that some nearby clusters are pulled in the same direction by the gravity of groups of other galaxy clusters. If this movement is fast, it can lead to errors in estimating cluster brightness. This kind of group movement can create the appearance that the pace of expansion of the universe is different in a given direction. Astronomers have seen similar effects in relatively close galaxies less than 850 million light years away, where gravitational pull is certainly controlling the movement of objects. Nevertheless, researchers expected the rate of expansion of the universe to dominate the movement of clusters spread over a larger area, up to 5 billion light years.

The second possible explanation is that the universe doesn't actually expand at the same rate in every direction. This may be caused, for example, by the heterogeneity of dark energy - a mysterious force that is responsible for accelerating the expansion of the universe. In other words, x-rays may indicate that dark energy is stronger in some parts of the universe than others, and thus causes the universe to expand unevenly.

Each of these two cosmological explanations can have significant consequences. Many cosmology studies, including x-ray galaxy cluster studies, are based on the assumption that the universe is isotropic.

For their research, scientists used a sample of 313 galaxy clusters, of which 237 were discovered by the Chandra space observatory during 191 observing days, and 76 by the XMM-Newton telescope observing them within 35 days. The above data were combined with two other X-ray samples including data from the XMM-Newton and ASCA telescopes. Hence, 842 different galaxy clusters were included in the study.



Surprise. The universe is expanding at different speeds in each direction

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