Russian scientists are developing a new-generation telescope to measure high-energy cosmic gamma rays. This will help to study in detail the center of our Galaxy, the Cygnus constellation, other objects of the galactic disk and detect signs of dark matter. How the work on the GAMMA-400 project is progressing, RIA Novosti was told by its scientific supervisor, Professor Arkady Galper (FIAN, MEPhI) and deputy scientific supervisor - chief designer Nikolai Topchiev (FIAN).
Ecumenical accelerators
The cosmic environment is permeated with electromagnetic radiation of the most varied nature. Sources can be solar flares, stars, pulsars, active galactic nuclei, processes associated with dark matter, and much more.
Gamma rays reaching the upper layers of the earth's atmosphere are photons of the highest energies - from millions to billions of electron volts. The same ones are obtained in charged particle accelerators - for example, LHC in Geneva or NIKA in Dubna. There accelerated particles - protons, light nuclei, electrons - interact with matter. As a result, new particles appear that decay or self-annihilate with the formation of high-energy gamma quanta.
For astrophysicists, gamma radiation is an invaluable source of information about distant worlds. It is possible that it will help uncover the secret of dark matter - a mysterious substance that provides a quarter of the mass of the Universe, so far inaccessible to direct observation in space and on accelerators.
Sources of gamma quanta - these are objects and processes capable of accelerating elementary particles to relativistic speeds / Illustration by RIA Novosti. Source: project * GAMMA-400 *.
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How to catch a bunch of energy
Gamma radiation, like all cosmic particles, except for neutrinos, is completely absorbed in the planet's atmosphere and spills onto the surface with a shower of various secondary traces, including Cherenkov optical radiation, collected using large ground mirrors. From the showers, you can approximately restore where the source that gave rise to them is.
To observe galactic gamma rays in their purest form, one has to go beyond the atmosphere. The first orbiting gamma-ray telescopes were launched by Soviet scientists from MEPhI in 1968 and 1970. The ANNA-3 gamma-ray telescope on the Kosmos-251 and Kosmos-264 satellites determined the direction of arrival and the energy of each gamma quantum separately.
Gamma quanta are neutral, and the only way to detect them is to force them to interact with matter, to measure the energy released and the direction of arrival of the photon. In this case, a pair of charged particles is formed - an electron and a positron.
This was the principle used by ANNA-3 and all subsequent devices. The last Soviet spacecraft, GAMMA-1, operated in orbit from 1990 to 1992. Now the USA has the palm. Since 2008, their FERMI / LAT has consistently scanned the entire sky in the gamma range.
Precision - Progress in Astronomy
The more accurately the telescope determines the energy of gamma quanta, the higher its angular resolution, the more valuable information it provides.
The American FERMI / LAT observes gamma radiation in the range from one hundred megaelectronvolts to one hundred gigaelectronvolts with an angular resolution of one tenth of a degree at the highest energies. For modern astrophysics, this is no longer enough, it is necessary to achieve greater accuracy. This fundamental problem is being solved by the Russian project "GAMMA-400" with the support of the RAS Council for Space and the Federal Space Program.
The new gamma telescope is designed for energies from 20 megaelectronvolts to 400 gigaelectronvolts, with a maximum angular resolution of one hundredth of a degree.
Reliable design, new results
Like its predecessors, GAMMA-400 consists of two fundamental elements: gamma-ray converters and detectors of electron-positron pairs. The first is a set of two dozen thin tungsten plates alternating with coordinate detectors that determine the direction of arrival of a gamma quantum.
For "GAMMA-400" the Kurchatov Institute proposes to use very precise fiber scintillation coordinate detectors, due to which a high angular resolution will be achieved. This will make it possible to very accurately measure the direction of arrival of high-energy gamma rays.
The second element is a large scintillation counter or a group of counters (calorimeter) where an electron-positron pair is absorbed and energy is measured.
Telescope device "GAMMA-400". K - converter of gamma quanta to electron-positron pairs, AC - anticoincidence detector, KK1, 2 - calorimeters / MEPhI, GAMMA-400.
In limiting orbits in search of high energies
The idea of a new gamma-ray telescope was proposed in 1987 by an outstanding Soviet physicist, later Nobel laureate Vitaly Ginzburg, astrophysicist Lidia Kurnosova and employees of her laboratory at FIAN. The name "GAMMA-400" means the ability to detect gamma quanta with an energy of 400 billion electron volts.
At that time, the search for dark matter was not yet so relevant. Scientists simply wanted to develop gamma astronomy, which lagged behind other areas of extra-atmospheric astronomy. However, the work dragged on for decades.
According to current plans, the device should be developed by the end of 2025. MEPhI, NIISI RAS, Kurchatov Institute, Institute of Physics of the National Academy of Sciences of Belarus participate in the project under the leadership of FIAN.
"GAMMA-400" has been significantly modernized, the angular resolution is a hundred times greater than it was once thought. The gamma telescope will be installed on the Navigator satellite platform, which is being developed at NPO Lavochkin. There will also be placed magnetic-plasma detectors and the ART-XC X-ray telescope - a more perfect copy of the Spectra-RG telescope.
Highly elliptical orbit of the device * GAMMA-400 *, which will allow observing pure cosmic gamma radiation / Project * GAMMA-400 *.
The gamma-ray telescope will be launched into a highly elliptical orbit, which will periodically change shape: from circular to elongated with an average radius of about 200 thousand kilometers. Thus, the device will not fall into the shadow of the Earth and will be able to measure cosmic gamma quanta outside the radiation belts of the planet.
Unlike FERMI / LAT, which scans the sky, GAMMA-400 will aim and continuously observe individual sources for a long time. Scientists want to investigate first the center of the Milky Way, then the region in the constellation Cygnus and then other objects in the plane of the galactic disk. Due to the lower angular resolution, the American telescope gives a blurry picture, without details. The Russian device will photograph everything with a high resolution, which will make it possible to distinguish between radiation sources.
Among the tasks is observing binary systems such as a pair of black holes. They accelerate particles in their vicinity to subluminal speeds and serve as powerful sources of gamma radiation. Also of interest are objects that emit not constantly, but periodically. To get a good look at and analyze the temporal characteristics in the gamma range, it will take more than one month of sighting observation.
* GAMMA-400 * will surpass the FERMI / LAT orbiting telescope by an order of magnitude in angular resolution. This will allow you to see the details in the plane of the galactic disk / Project * GAMMA-400 *.
In search of dark matter particles
The scientific community hopes to test with the help of "GAMMA-400" the hypothesis about the nature of dark matter particles, the reality of which is now no longer in doubt. There is a lot of circumstantial evidence about dark matter - in particular, galactic halos or tracer stars orbiting an invisible center of mass.
According to one model, dark matter can be composed of WIMPs - this is the name for hypothetical massive particles that participate only in weak and gravitational interactions. It is assumed that high-energy gamma radiation with the energy of gamma quanta of the order of the WIMP mass is generated during the decay of the WIMP or self-annihilation of two particles.
An important discovery in this direction was made in the PAMELA experiment carried out in orbit from 2006 to 2016. The device detected an excess of very high-energy positrons in cosmic rays. The researchers suggest that they were generated not only by a local source (for example, a pulsar), but also by the decay or self-annihilation of dark matter particles. Its clumps can hide behind the clouds of the interstellar medium, and "GAMMA-400" is able to detect them.
Tatiana Pichugina