Translated material
Hot spot
Earlier in the archive of electronic preprints an article was published. The International Collaboration Telescope Array announced the discovery of anisotropy of space rays of super -high energies. At the same time, an article with a detailed description of the result was published in the electronic preprint archive. Anisotropy has the form of spots in the sky, where 19 particles with energy above 5.7x1019 EV with the expected 4.5 came from a circle of 20 °.
First of all about installation. Telescope Array is an array of scintillation detectors covering an area of about 700 km2. Detectors go with a step of 1.2 km, there are 507 of them in total, each area is 3 m2. In addition to scintillation detectors, the installation includes optical telescopes for registering a fluorescent glow. Such installations are designed to register wide atmospheric rain particles. When a particle of huge energy flies into the atmosphere and interacts in its upper layers, it causes a cascade of interactions that gives rise to billions of secondary particles. To register such a downpour and measure its parameters, it is not necessary to tightly block the surface- a fairly rare mesh. By the way, the energy of such a particle (under 1020 EV) is quite macroscopic, several joules. Like a pebble 30 g, thrown at a speed of 20 m/s. The threshold of energy detection for Telescope Array is 1018 eV.
Now Telescope Array is the largest in the northern hemisphere and the second installation of this type in the world in size (the largest is the named after Pierre Ozhe in Argentina). It is located in the desert area of the state of Utah.
Why is anisotropy looking for such huge energies (almost two orders of magnitude higher than the threshold of detection)? It, of course, is looking for all energies, but on super -highs it is more natural. Firstly, such particles are poorly deviated in the magnetic field of the galaxy. Secondly, they also deviate less in the intergalactic magnetic field, the tension of which, however, is unknown. And thirdly, such particles do not fly from great distances, at which the universe is almost isotropic. They come only from a distance of dozens of mega-park, on which there are large clusters of galaxies and a local large-scale structure is well expressed. The reason why such particles do not fly far is the effect of Graisen - Zatsepina - Kuzmina. They interact with photons of relict radiation, giving birth to pi-mesons and losing energy on this. The threshold, of course, is smooth, and any specific value of energy is very conditional. The value of 1020 eV is usually mentioned.
It would be extremely interesting to detect anisotropy of particles of such energy. Firstly, it is still not known exactly where and how particles are accelerated to such energies. If you find where they fly from, this would greatly help to find out their origin. In addition, seeing a source in the stream of charged particles, one could put the upper limit on the intergalactic magnetic field, and maybe measure it.
The statistical significance of a hot spot seems to be large enough to pay attention to it. “In the forehead” it will be 5.1 sigma, but if you put the question correctly: “What is the probability of a random appearance of such a spot somewhere in the sky?”, Then, according to the authors of the article, the significance will drop to 3.4 sigma (probability-1/3000)-and this is no longer so, many effects of such statistical significance have not been confirmed. This level is enough to declare the opening. Personally, the following circumstances are suspicious.
1. The value of the effect is suspiciously large - 19 with an average of 4.5, that is, a four -time excess above the average. In theory, this should mean that in this direction there is something monstrous, which should be easily identified by other manifestations. Such an object could be the center of our galaxy, but it is not there at all. In general, when the statistics are small, the first to emerge, of course, very strong effects and then usually float away.
2. In the direction of the hot spot there is just nothing particularly remarkable. It lies away from the main local element of a large -scale structure and away from the nearest large clusters of the galaxies. The only thing that is there is the “sleeve” from the galaxies connecting our group with the accumulation of galaxies in the constellation Virgin. If it were the cluster itself in Virgo, it would be much more convincing - this is the largest close cluster of galaxies. However, there is a hope that the spot can just be a “way” of cluster in the Virgin, shifted to the side due to the magnetic field of our galaxy (private message from Igor Tkachev).
3. The circumference threshold by energy 5.7x1019 is taken a priori - it is borrowed from the experiment of another collaboration. From a methodological point of view, this is correct, but still I would like to see how the statistical significance changes depending on this threshold. Such a picture can help distinguish between a statistical fluctuation from a real effect.
In the light of such doubts (which the authors of the experiment probably understand) and in view of a small statistical significance, the question is legitimate-is this result of publication and press conference that raised the wave in the media? This result, of course, deserves publications. Of course, the attention of the scientific community should be attracted to the effects that do not reach complete confirmation (marginally significant), and there is nothing shameful in the fact that he can resolve over time. This is the usual practice of scientific research. But with regard to the raising of the wave in the media, there are certain doubts. On the one hand, collaborations need money for the development of installation, and the attention of the press can contribute to this. On the other hand, if the general public sees that the high-profile statements of scientists are not often confirmed, it will generally cease to believe in any statements by scientists. In short, life is complicated.
As for the prospects - undoubtedly, in the foreseeable time, the situation with a hot spot will become clear, and even if the conclusion is not confirmed, the anisotropy will be discovered sooner or later. The fact is that such installations can increase almost unlimitedly - there would be money. In the foreseeable future, Telescope Array will grow four times. And then let's see!