The erosita instrument on the spectrum roentgen gamma (SRG) space telescope mission, jointly launched by Russia and Germany, has recently completed the classification of more than 1 million high-energy x-ray sources, which is more than the previous record. < / P > < p > as can be seen from the published pictures, our sky is illuminated by X-rays, and the energy in the electromagnetic spectrum is much higher than that in visible light. Red represents low energy area (0.3 ~ 0.6 keV), green represents medium energy (0.6 ~ 1 keV), and blue represents high energy (1 ~ 2.3 keV). Along the center line of the elliptical image, we see the Milky way, which appears as the only high-energy source; this is due to the large amount of dust and particles scattered in the night sky, which can be seen. Bright yellow and green patches indicate high-energy events such as supernovae and supermassive black holes. The white dots that appear in the whole image are close to one million X-ray sources. < / P > < p > you may be familiar with the amazing visible images taken by the Hubble Space Telescope, but the rest of the spectrum contains valuable information about the Milky way and the universe. Radio astronomy was born in 1932, when Karl jansky was studying what interfered with radio signals across the Atlantic. He set up an antenna in Bell laboratory to receive radio wave signals from all directions, and finally determined that radio astronomy studies celestial bodies at radio frequency through electromagnetic wave spectrum. Its technology is similar to that of optics, but because of the long wavelength observed by radio telescope, it is more huge. Radio waves can penetrate the earth’s atmosphere, allowing us to observe them from the earth’s surface, such as using Atacama’s large millimeter / submillimeter array. However, X-rays cannot penetrate the earth’s atmosphere and must be observed from space or at very high altitudes. It was not until the 1960s that the first space program to observe extrasolar X-ray sources emerged. < / P > < p > instruments like erosita can observe the most violent events in the universe around us. X-rays are high-energy electromagnetic radiation of short wavelengths that are released when gases are heated to millions of degrees. When a gas is compressed or accelerated, it also emits X-rays. When the star dies, huge supernovae explode, compressing the gas in the shock wave, and X-rays are released from the flare. In the X-ray spectrum, we can also find remnants of dead stars, or neutron stars (neutron stars are so dense that a small piece of neutron star matter is heavier than all people on earth) or black holes. Black holes don’t actually emit X-rays, they’re actually black, because all the electromagnetic radiation is sucked in; but when the black hole spins and produces a magnetic field, the matter gathered in the singularity does signal in the X-ray spectrum. There is a class of binary systems that emit bright X-ray radiation called “X-ray binaries”. One of them is a dense star, usually a neutron star or a black hole. The binary system consists of “accelerators” and “donors” with large gravitation. The gas provided by the latter is overheated when accelerating to a neutron star or black hole. < / P > < p > the sun also emits X-rays, although weaker. Scientists use X-rays to study an interesting problem in solar physics. The corona, the outer layer of the sun, is much hotter than the rest of the sun, with temperatures ranging from 1 million to 3 million K, while the average temperature of the sun is about 5570 K. The X-ray radiation from solar flares can be used to study the magnetic field and its effect on coronal heating. Finally, this new X-ray source map may be the key to understanding dark matter. In 2012, Jee et al. First observed the colliding galaxies at the Chandra X-ray Observatory. They showed obvious separation in X-ray emission and mass distribution. According to some theories, this is caused by the gravitational lens caused by dark matter, which leads to the bending and shearing of light. This is strong evidence of the existence of dark matter. The sky survey of erosita will provide a large number of X-ray source data and may provide clues for the study of dark matter. X-ray astronomy is a branch of astronomy which takes the X-ray radiation of celestial bodies as the main research method. The energy of photons is usually expressed in electron volts (EV), and the objects of observation are X-rays ranging from 0.1kev to 100keV. Among them, 0.1 ~ 10KeV X-ray is called soft ray, and 10 ~ 100keV is called hard ray. Because X-ray belongs to high-energy electromagnetic spectrum, X-ray astronomy and gamma ray astronomy are called high-energy astrophysics. The objects that radiate X-ray in the universe include X-ray binaries, pulsars, gamma ray bursts, supernova remnants, active galactic nuclei, solar active regions, and high-temperature gases in galaxy clusters. Because X-rays cannot penetrate the earth’s atmosphere, X-ray sources can only be observed at high altitude or outside the atmosphere. Therefore, space astronomical satellites have become the main tool of X-ray astronomy. Since 1940s, X-ray astronomy has shifted from simple X-ray source observation to fine-grained X-ray spectroscopy. High resolution X-ray spectra were first obtained by spectrometers on Einstein’s satellite. Today, the Chandra X-ray telescope and XMM Newton satellites enable astronomers to identify characteristic lines. The space X-ray satellites have acquired the spatial resolution no less than the ground-based large-scale optical telescopes. At the same time, the level of data processing is also improving rapidly. All these make X-ray astronomy one of the most abundant and active fields in astronomy. (Rentian) < A= target=_ blank>After 12 years, “world class Super project” Shantou Bay Tunnel ushers in a historic breakthrough today