Indo-Asian News Service

A Chinese satellite which was sent to the skies to look for evidence of the annihilation or decay of dark matter particles in space has detected unexpected and mysterious signals in its measurement of high-energy cosmic rays, bringing scientists closer to proving the existence of the invisible matter. The mysterious dark matter is believed to comprise a quarter of universe.

The satellite, Dark Matter Particle Explorer (DAMPE), also called Wukong or "Monkey King", has measured more than 3.5 billion cosmic ray particles with the highest energy up to 100 tera-electron-volts (TeV), including 20 million electrons and positrons, with unprecedented high energy resolution, Xinhua reported. Precise measurement of cosmic rays, especially at the very high energy range, are important for scientists to look for traces of dark matter annihilation or decay, as well as to understand the universe's most energetic astrophysical phenomena, such as pulsars, active galaxy nuclei and supernova explosions.

"DAMPE has opened a new window for observing the high-energy universe, unveiling new physical phenomena beyond our current understanding," Chang Jin, Chief Scientist of DAMPE and Vice Director of the Purple Mountain Observatory of the Chinese Academy of Sciences (CAS), said.

The initial detection results on the precise measurement of the electron and positron spectrum in an energy range between 25 giga-electron-volts (GeV) and 4.6 TeV were published in the latest issue of the journal Nature. "Our data may inspire some new ideas in particle physics and astrophysics," said Chang. Dark matter, which cannot be seen or touched, passes right through us as if we do not exist. The ghost-like material is one of the great mysteries of science.

Scientists calculate that normal matter — such as galaxies, stars, trees, rocks and atoms — accounts for only about five per cent of the universe. However, about 26.8 per cent of the universe is dark matter and 68.3 per cent dark energy. China sent DAMPE into an orbit of about 500 kilometres above the earth on 17 December. Based on the satellite's data, scientists drew the cosmic ray electron and positron spectrum.

To their surprise, scientists found a break at around 0.9 TeV and a strange spike at around 1.4 TeV on the spectrum. "We never expected such signals," Chang said. "The spike might indicate that there exists a kind of unknown particle with a mass of about 1.4 TeV," Chang said. "All the 61 elementary particles predicted by the standard model of particle physics have been found. Dark matter particles are beyond the list. So if we find a new elementary particle, it will be a breakthrough in physics," he added.

More than 100 Chinese scientists and engineers, together with those from Switzerland and Italy, took part in the development of DAMPE and the analysis of its data. Researchers have ruled out the possibility that the unusual signals are caused by a malfunction of the satellite's detectors. Independent analyses from five different teams all came to the same conclusion, said Chang. Some other probes dedicated to exploring the evidence of annihilation or decay of dark matter particles in space are NASA's Fermi Space Telescope and the Alpha Magnetic Spectrometer (AMS-02), a particle physics detector operating on the International Space Station (ISS).