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    Home > Biochemistry News > Biotechnology News > Dense stars, supermassive black holes... How do we detect the extreme side of the universe?

    Dense stars, supermassive black holes... How do we detect the extreme side of the universe?

    • Last Update: 2020-09-14
    • Source: Internet
    • Author: User
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    Zhang Bo (National Observatory of the Chinese Academy of Sciences) High-energy astrophysics is one of the hot topics in contemporary astronomy research.
    in the X-ray and gamma-ray sky, from the dance of death of the twin stars to the supermassive black hole at the center of the galaxy, the most violent cerial phenomena have taken place.
    , however, exploring the extreme universe is not easy, and in addition to going into space to avoid absorption of the Earth's atmosphere, special high-energy photon detectors are needed.
    these high-energy detectors, both in working and in appearance, are far from the telescopes that people think they are.
    optical telescopes collect and image light through reflection or refraction, and even if the wavelength extends to the infrared or radio band, the instrument uses a reflective surface to focus on astro-radiation.
    But at the other end of the electromagnetic spectrum, once it crosses a very ultraviolet region with a wavelength of tens of nanometers and a single photon energy greater than a few tens of electron volts, the traditional focus is unsustainable.
    these ultraviolet or X-ray radiations can penetrate matter directly or be absorbed, voiding refractions or reflections that we are familiar with.
    X-ray photons, which are almost parallel to mirror incident (i.e., skimming), can also be fully reflected, just as stones can bounce off water at high speeds.
    X-ray focusing telescopes can be made by selecting materials with low X-ray absorption rates to build mirrors and reasonably combining mirror shapes.
    most classic layout of the X-ray Focus Telescope is the light path shown in the image below, where the skimming light passes through the parabola and double surfaces in turn to reach the focal surface.
    , if multiple sets of mirrors are combined into a sleeve, the telescope's light-collecting area can be effectively increased within a limited volume.
    image depicts four layers nested with each other, the same structure as NASA's Chandra X-ray Observatory.
    /CXO When photon energy continues to increase to reach the range of hard X-rays or soft gamma rays, skimming doesn't help, and we're going to switch to unfocused coding masks for observation.
    Simply put, the mask body is alternately arranged by transparent and opaque metal mask elements for high-energy photons, and the real image of the radiation source can be inferred by the position and intensity distribution of the mask elements projected on the receiving instrument.
    therefore, when designing masks, the key is to ensure that photon projection results from different angles are unique in order to achieve an accurate reduction of the source area.
    Left: Coded masks work as indicated, red and blue radiation sources through the mask left on the receiving instrument projection shape is consistent, but the location is different, you can restore the image (Figure / ESA);
    , however, the higher the photon energy segment you want to receive, the heavier the masker must be until it exceeds the rocket's carrying capacity.
    to catch a glimpse of the higher-energy hard gamma rays, people turned to the particle nature of light.
    Its detection principles include the release of flash from high-energy photons exciting fluorescent materials, the generation of electron-cavity pairs by high-energy photons within semiconductors, and the conversion of high-energy photons into positive and negative electrons after interacting with the material layer plate.
    these principles correspond to strommers, semiconductors and particle pairs to produce detectors, and their performance and applications are different.
    but in addition to gamma photons, charged cosmic rays allow these detectors to record similar signals, so a shield wrapped around the outside of the detector is essential.
    shields only react with charged particles, and only if they are not triggered can it be determined that the detection signal is coming from photons.
    to the highest-energy areas (a single photon has trillions of times the energy of visible light), the number of photons originating from celestial bodies is scarce, and space exploration is not cost-effective, so observations are more suitable on the ground.
    this time, the absorption of high-energy photons by the atmosphere can be used: the incoming photons transfer energy to the atmospheric atoms, causing the latter to break up and trigger cascading clusters of particles that flow out of a large number of energy step by step.
    if the initial transfer of energy is large enough to allow clusters of particles to travel faster than the speed of light in the air, the particles will produce Cherenkov radiation, similar to the sound storm when the aircraft broke the sound barrier.
    this dark glow is the target of the Atmospheric Imaging Cherenkov telescope, which can push back the gamma source based on the direction and distribution of Cherenkov's light.
    water Cherenkov telescope is to capture high-speed clustered particles through a dedicated pool of Cherenkov light, the rest of the same as the former.
    atmospheric imaging Cherenkov telescope array HESS.
    (Figure/HESS Cooperative Group) In addition to the astronomical detectors described above, the development of new instruments is also under way, such as the Lauer lens detector, which uses crystal diffraction to focus on gamma rays, the oversized lobster eye-sweeping light path, the highly sensitive multi-layer silicon chip pore-type flare mirror, and so on.
    predictably, with the rapid development of detector technology, the most extreme side of the universe will be more clearly displayed to the world.
    the pore silicon optical system for the next generation of X-ray telescopes, equivalent to tens of thousands of stacked mirrors.
    (Photo/Cosine Research) Source: Zhang Bo Instrument network.
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