A researcher at the Chinese Academy of Sciences explains about the data sent back from the space by Wukong in Dec. 24, 2015. (Photo/Xinhua)
Hunting in the darkness of the universe, the hunters still don't know how their prey looks like or when and where it might pop up.
Their best clues are hidden in the chains of figures and diagrams entering computers in an inconspicuous white building of the Purple Mountain Observatory in downtown Nanjing, capital of east China's Jiangsu Province. The computers are receiving data from the Dark Matter Particle Explorer (DAMPE), 500 kilometers away in space.
Chang Jin, chief scientist of China's DAMPE program, describes the search for the missing mass of the universe: "It must be there. But we don't know if we will be lucky enough to catch it, or even if it is a bear or a rabbit."
Scientists believe that only around 5 percent of the total mass-energy of the known universe is made up of ordinary matter -- protons, neutrons, electrons -- so dark matter and dark energy make up the rest.
Dark matter, like a ghost of the universe, does not emit or reflect enough electromagnetic radiation to be observed directly, and is one of the great mysteries of modern science.
A theory of scientists who could not understand the missing mass and strangely bent light from faraway galaxies, dark matter is widely accepted in the physics community even though its existence has never been concretely proven.
Understanding dark matter could, therefore, give us a clearer idea about the past and future of galaxies and the universe, and will be revolutionary for the fields of physics and space science, Chang says.
The universe hides its secrets well. And the hunters need a good "sword."
Scientists compare DAMPE, nicknamed "Wukong" or "Monkey King", to a sword sweeping for traces left by the "ghost" of universe using the widest-ever observation spectrum and highest-ever energy resolution equipment of any probe in the world.
The satellite was successfully sent into orbit on Dec. 17, 2015. Since the launch, Chang has worried every day whether its 76,000 small detectors are working properly; whether the data are reliable; whether the storage and computing capability of the computer are enough.
DAMPE cost only one seventh of NASA's FERMI Space Telescope and one twentieth of the AMS-02 particle detector on the international space station.
Chang argues the satellite should be worth the money.
GLIMPSING THE "GHOST"
When Chang started work at the Purple Mountain Observatory in 1992, he chose to specialize in the observation of high-energy electrons and gamma rays, because no scientist had ever done that before.
However, it required expensive equipment that China could not afford in the 1990s. So Chang developed a new and cheaper method to observe high-energy electrons and gamma rays.
He convinced U.S. scientists to include his observation method in the ATIC program, which released a balloon-borne instrument over Antarctica to measure the energy and composition of cosmic rays from the end of 2000 to the beginning of 2001.
The data analysis revealed an unexpected surplus of high-energy electrons that could not be explained by the standard model of cosmic ray origin, in which electrons are accelerated in sources such as supernova remnants and then propagate through the galaxy.
Chang believes the surplus possibly resulted from the annihilation of dark matter.
In the following years, Chang and his partners improved their equipment and method, and conducted three more observations above Antarctica.
