One basic idea of cosmology is that if the scale of observation is large enough, then you look the same in all directions. This is the cognitive pillar of humanity about the history and destiny of the universe.
On April 8th, a result of a collaboration between the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) challenged this. Konstantinos Miggas, a cosmologist at the University of Bonn in Germany who is leading the study, said: “That pillar may have cracks.” For years, astronomers have assumed that after the Big Bang, the expansion rate in all directions is the same, so-called isotropy. In this case, although there are some local differences in the universe, each direction has the same properties on a large scale.
A common analogy is toast, and cosmic substances such as galaxies are raisins inside. During the baking process, the raisins spread as the bread swells, but is generally uniform.
The isotropic universe hypothesis is supported by the Cosmic Microwave Background Radiation (CMB).
Cosmic microwave background radiation (CMB) is a group of ancient photons. In the very early days, the universe was filled with various elementary particles and was in a state of chaotic plasma. It was not until about 380,000 years after the Big Bang that protons and electrons combined into stable neutral hydrogen atoms, and the universe became transparent and allowed At that time, photons traveled freely. This group of photons reached Earth after traveling for about 13.7 billion years, just like a photo of the universe from 13.7 billion years ago.
This “380,000-year-old photo” tells us that at that time the universe expanded at the same speed in all directions. So, is the universe still the same today?
This “380,000-year-old photo” tells us that at that time the universe expanded at the same speed in all directions. So, is the universe still the same today?
If the universe has always been isotropic, then galaxy clusters with the same temperature and similar distances should look equally bright. The team used a powerful and novel method to test this.
The galaxy cluster is filled with extremely hot gas, the temperature of these gases is related to the amount of X-rays it produces, called X-ray brightness. This measurement method will not be affected by the expansion of the universe. Next, the research team calculated the brightness in another way that would be affected by the expansion rate of the universe, and compared the two. The verification results of more than 800 galaxy clusters are contrary to theory.
Thomas Reiprich, an astronomer at the University of Bonn who participated in the study, said: “We see that star clusters with the same properties and similar temperatures are in a The brightness in the direction is lower than expected, and in the other direction is higher than expected. The difference is quite significant, about 30%. These differences are not random, but show a clear pattern according to our observation direction. “
The research team further ruled out the influence of the gravitational field of gas and dust clouds blocking the line of sight or the supermassive structure.
If the universe really no longer expands evenly, then astronomers will be busy. In an isotropic universe, the same set of parameters and equations are universally applicable, and the anisotropic universe needs to be reconsidered on very distant scales.
As for the cause of uneven expansion, the mysterious dark energy that is thought to occupy 69% of the universe may be an explanation.
It is worth noting that the observation data of this study comes from several predecessor space telescopes, and the number of samples is very limited. ESA’s XMM Newton Telescope and NASA’s Chandra Telescope were both launched in 1999.
ESA ’s flagship Euclidean telescope is scheduled to set sail in 2022 with the theme of cosmic expansion and dark energy. By taking billions of images of galaxies, it may provide more accurate evidence.