An artist illustration of China's Dark Matter Particle Explorer – named "Wukong" after the legendary Sun Wukong, the Monkey King – studies cosmic rays to help scientists understand the origins of the dark matter.
Credit: Chinese Academy of Sciences
By badyzing cosmic rays in space, China's "Monkey King" satellite is now helping to identify the identity of dark matter, according to a new study.
The dark matter particle explorer (DAMPE), launched in 2015, is China's first space observatory. The goal of DAMPE is to help find the origins of dark matter: the mysterious and invisible substance that researchers suspect constitutes approximately five-sixths of all the matter in the universe.
DAMPE is nicknamed "Wukong" after Sun Wukong, the Monkey King, the mischievous hero of the legendary Chinese tale "Journey to the West". "Wu" means "understanding" and "kong" means "emptiness", so Wukong can also mean "understanding the void", therefore, the name underlines the mission of DAMPE to help scientists understand dark matter . [The Search for Dark Matter in Images]
DAMPE is specifically designed to detect the higher energy light rays, known as gamma rays, as well as cosmic rays. The latter are particles that slide through outer space with extraordinarily high amounts of energy. Many cosmic rays are composed of nuclei of atoms, but some are electrons, while others are counterparts of positively charged antimatter electrons known as positrons.
Some models of dark matter suggest that it can be decomposed into cosmic rays, specifically, pairs of electrons and positrons. When these positrons strike electrons, they annihilate each other, releasing gamma rays. However, there are many other potential sources of cosmic rays and gamma rays, such as pulsars, which rapidly rotate collapsed stars, or supernova remnants, which are remains of stars that died in catastrophic explosions. DAMPE measures the amount of energy in gamma rays and cosmic rays to help shed light on what its sources are.
Previous experiments based on balloons or space that badyze cosmic rays only directly measured energies of up to 2 trillion electron volts, while arrays based on telescopes could indirectly measure energies of up to 5 trillion electron volts. (One trillion electron volts equals the amount of kinetic energy packaged by a flying mosquito)
In comparison, DAMPE can detect cosmic and positron electron electrons with energies of around 10 trillion electron volts. "It extends the direct measurement of electrons and positrons of cosmic rays to the highest energies so far," Jordan Goodman, a particle astrophysicist at the University of Maryland, who was not involved in the DAMPE investigation, told Space.com. [100 Years of Cosmic Rays: The Discovery Explained]
Until now, DAMPE has detected more than 3.5 billion cosmic rays, the most energetic of which exceed 100 trillion electron volts. It is expected that DAMPE will detect more than 10 billion cosmic rays during its projected life of more than five years.
Notably, DAMPE found a "spectral break" – a decrease in the number of electrons and cosmic ray rays – to approximately 900 billion electron volts. "No one is sure why there is a break," Goodman said.
Previously, the H.E.S.S. array in Namibia and the Electron Calorimetry Telescope on the International Space Station had seen signs of this spectral breakdown, but the Fermi Gamma Ray Space Telescope did not.
"Our measurements have clarified the behavior of the electron and positron spectrum in trillion-electron-volt energies," study co-author Yi-Zhong Fan, a particle astrophysicist at the Academy of Sciences of China in Nanjing. . "The first results of DAMPE demonstrate its ability to explore new astrophysics."
Dark matter particles could explain this spectral jump if the mbades of those particles are just below 900 billion electron volts, Goodman said. (Energy is equivalent to mbad, as demonstrated by Einstein's famous equation E = mc ^ 2). As such, these findings challenge models that suggest that dark matter particles may have different mbades.
On the other hand, this spectral cut could be due to the cosmic rays of pulsars or supernova remnants that are somehow cooling down on their way through space, Fan said. "Either way, we are now getting solid data against which any model should be tested," Goodman said.
The scientists detailed their findings in the November 30 issue of the journal Nature.