All-sky X-ray star map reveals the mystery of dark matter

 According to foreign media reports, the eRosita instrument carried by the Russia-Germany “Spectrum-Roentgen-Gamma” (Spectrum-Roentgen-Gamma, referred to as SRG) space telescope mission has recently completed the classification of more than 1 million high-energy X-ray sources. This number exceeds previous records for this study.

　　 It can be seen from the published pictures that our sky is illuminated by X-rays, and the energy in the electromagnetic spectrum is much higher than visible light. Red represents the low energy region (hermes outlet), green represents the mid-range energy (0.6~1 keV), and blue represents high energy (1~2.3 keV). Along the midline of the elliptical image, we see the Milky Way, which appears as the only source of high energy; this is due to the large amount of dust and particles scattered in the night sky that can be seen by us. Bright yellow and green patches indicate high-energy events, such as supernovae and supermassive black holes. The white dots appearing in the entire image are nearly one million X-ray sources.

　　You may be familiar with the amazing visible light 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 transatlantic radio signals. He set up an antenna at Bell Labs to receive radio wave signals from all directions, and finally determined.

Radio astronomy uses the electromagnetic spectrum to study celestial bodies at radio frequencies. The technology is similar to optics, but because the wavelength observed by radio telescopes is longer, it is even larger. Radio waves can penetrate the earth’s atmosphere, allowing us to observe them from the surface of the earth, such as using the Atacama large millimeter wave/submillimeter wave array. However, X-rays cannot penetrate the earth’s atmosphere, so observations must be made from space or very high altitudes. It was not until the 1960s that the first space program to observe X-ray sources outside the solar system appeared.

　　 Instruments like eROSITA can observe the most dramatic events in the universe around us. X-rays are short-wavelength, high-energy electromagnetic radiation that are released when gas is heated to millions of degrees. When gas is compressed or accelerated, X-rays are also emitted. When the star dies, a huge supernova bursts into the shock wave to compress the gas, and X-rays are released from the flare. In X-ray spectroscopy, we can also find the remnants of dead stars, or neutron stars (neutron stars are very dense, and a small piece of neutron star material is heavier than everyone on Earth) or black holes. Black holes do not actually emit X-rays, they are actually black because all electromagnetic radiation is sucked in; however, when the black hole rotates and generates a magnetic field, the matter gathered in the singularity does indeed appear in the X-ray spectrum. Signal in. One type of binary star system that emits bright X-ray radiation is called "X-ray binary star", one of which is a compact star, usually a neutron star or a black hole. The binary star system consists of an "accelerator" and a "donor" with greater gravity. The gas provided by the latter is overheated when accelerating toward a neutron star or black hole.

The sun also emits X-rays, albeit faintly. Scientists use X-rays to study an interesting problem in solar physics. The corona is the outer layer of the sun and is much hotter than the rest of the sun. Its temperature is 1 to 3 million K, while the average temperature of the sun is about 5570 K. X-ray radiation from solar flares can be used to study the magnetic field and its effect on the heating of the corona.

　　 Finally, this new X-ray source map may be the key to understanding dark matter. In 2012, Jee et al. observed the colliding galaxies at the Chandra X-ray Observatory for the first time, and they showed obvious separation in X-ray emission and mass distribution. It is theorized that this is caused by the gravitational lens caused by dark matter, which leads to the bending and shearing of light. This is strong evidence for the existence of dark matter. eROSITA's sky survey will provide a large amount of X-ray source data and may provide clues for dark matter research.

X-ray astronomy is a branch of astronomy in which the X-ray radiation of celestial bodies is the main research method. The energy of photons is usually expressed in electron volts (eV), and the observation object is X-rays from 0.1keV to 100keV. Among them, 0.1~10keV X-rays are called soft rays, and 10~100keV are called hard rays. Because X-rays belong to the high-energy electromagnetic spectrum, X-ray astronomy and gamma-ray astronomy are both called high-energy astrophysics.

　　 The celestial bodies that radiate X-rays in the universe include X-ray binaries, pulsars, gamma-ray bursts, supernova remnants, active galactic nuclei, solar active regions, and high-temperature gas in galaxy clusters. Since X-rays cannot penetrate the earth’s atmosphere, X-ray sources can only be observed at high altitudes or outside the atmosphere. Space astronomy satellites have therefore become the main tools of X-ray astronomy.

　　 Since the 1940s, X-ray astronomy has shifted from simple X-ray source observation to fine X-ray spectroscopy. The high-resolution X-ray spectrum was first obtained by a spectrometer on the Einstein satellite, and now the Chandra X-ray telescope and XMM-Newton satellite allow astronomers to identify characteristic spectral lines. The space X-ray satellites have obtained the spatial resolution capability comparable to that of large-scale optical telescopes on the ground. At the same time, the level of data processing is also rapidly improving. All of these have made X-ray astronomy one of the most abundant observational data and the most active research fields in astronomy. One.