China releases first batch of gamma photon data from dark matter particle explorer

China released the first batch of gamma photon data obtained by the Dark Matter Particle Explorer satellite-based telescope on Tuesday, allowing scientists to improve their hunt for elusive dark matter.

Dark matter is a type of substance that cannot be directly observed but is believed to account for around 80 percent of the mass of the universe. Gamma photons are the most energetic particles of light in the electromagnetic spectrum.

The telescope, also known as Wukong or Monkey King, has collected data on around 10.7 billion high-energy cosmic rays since its launch in 2015, according to the National Space Science Data Center and the Purple Mountain Observatory of the Chinese Academy of Sciences.

The data released was recorded from Jan 1, 2016 to Dec 31, 2018, and included 99,864 gamma photons. More data sets will be released in the future, the two institutions said.

The missions of the telescope include studying properties of dark matter by taking a closer look at high-energy gamma rays and electrons, as well as examining the possible origins and acceleration mechanism of cosmic rays, high-energy protons and atomic nuclei that move through space at nearly the speed of light.

Chang Jin, a CAS academician and chief scientist of the Wukong telescope, said in a public lecture that the high-energy cosmic rays may be generated in the annihilation or decay of dark matter.

Since gamma photons do not carry an electric charge like protons and electrons, they are less likely to be affected by the magnetic field of other celestial bodies and events, hence they may carry more accurate information about dark matter and the origins of cosmic rays, he said.

In 2019, an international team of researchers studying data collected by the Wukong telescope measured cosmic ray protons up to 100 trillion electron volts with high precision for the first time, according to a study published in the journal Science Advances.

Before the launch of Wukong, balloon experiments could only directly measure cosmic rays with energies up to 2 trillion electron volts, while ground-based telescope arrays could indirectly measure such particles with energies up to about 5 trillion electron volts.

One of the biggest and strangest discoveries made by Wukong is that there is a "spectral break", a drop in the number of cosmic ray electrons and positrons, at about 900 billion electron volts, and nobody knows why this dip exists, according to a study published in the journal Nature in 2017.

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