The universe is a vast, mysterious place, and for decades, scientists have been trying to unravel one of its biggest secrets: the origin of cosmic rays. These high-energy particles bombard Earth from outer space, and understanding where they come from is crucial to unlocking the secrets of the cosmos. Now, a groundbreaking discovery by Chinese scientists using the Large High Altitude Air Shower Observatory (LHAASO) is providing some of the answers.
Scientists have found that black holes, those cosmic behemoths that devour matter and spew out powerful jets, act as potent particle accelerators. They may be key players in creating the high-energy cosmic rays we detect here in the Milky Way.
"The studies not only uncover the key mechanisms behind cosmic ray origins but also advance our understanding of the extreme physical processes of black hole systems," explained Cao Zhen, the principal investigator of LHAASO and an academician of the Chinese Academy of Sciences (CAS).
So, what exactly are cosmic rays? They are charged particles, primarily protons, that travel through space at incredible speeds. The origin of these rays has been a major puzzle for astrophysicists. One intriguing aspect of cosmic rays is their energy spectrum, which shows a distinct "knee" around 3 PeV (peta-electron volt). This "knee" represents a turning point in the energy levels of the cosmic rays, and understanding its origin has been a major goal of research.
The LHAASO team's research has pointed the finger at microquasars, which are black holes that are devouring material from companion stars. These microquasars, driven by accretion onto black hole systems, act as powerful particle accelerators within our galaxy and are likely the sources of the "knee".
This research, published in National Science Review and Science Bulletin, involved researchers from the Institute of High Energy Physics of the CAS, Nanjing University, the University of Science and Technology of China, and La Sapienza University of Rome, among other institutions.
Here's where it gets interesting: Black holes, some of the most enigmatic objects in the universe, create relativistic jets when they consume material from companion stars in binary systems, forming what scientists call "microquasars." LHAASO has been instrumental in detecting ultra-high-energy gamma rays from five microquasars.
For instance, the analysis of the microquasar SS 433 revealed that the proton energy in this system exceeds 1 PeV. The power output per second is equivalent to the energy released by 400 trillion of the most powerful hydrogen bombs! Furthermore, the gamma-ray energy from the microquasar V4641 Sgr reached 0.8 PeV, implying that the particles generating these gamma rays likely had energies exceeding 10 PeV.
"These results prove that microquasars are significant PeV particle accelerators in the Milky Way," Cao said.
To fully understand the "knee" in the cosmic-ray spectrum, it's essential to precisely measure the energy spectra of various cosmic ray species.
LHAASO, located in the Sichuan Province of southwest China at an elevation of approximately 4,410 meters above sea level and covering an area of 1.36 square km, is a world-leading facility for cosmic ray observation and research. It uses advanced multi-parameter measurement techniques to analyze cosmic rays. The measurement revealed an energy spectrum structure that was entirely unexpected.
"The new discovery not only marks a significant advancement in resolving the long-standing mystery of the 'knee' origin, which has puzzled the academic community for nearly 70 years, but also offers crucial observational evidence for understanding the role of black holes as the origin of cosmic rays," Cao said.
LHAASO, designed, constructed, and operated by Chinese scientists, has become a leader in high-energy cosmic-ray research. Its sensitivity in both gamma-ray astronomical exploration and cosmic-ray precision measurements has led to impactful discoveries, contributing to our understanding of the extreme physical processes in the universe.
But here's where it gets controversial: While this research provides compelling evidence, the exact mechanisms by which microquasars accelerate cosmic rays are still being investigated. Some scientists may have different interpretations or theories about the specific processes involved.
What do you think? Are you surprised by these findings? Do you have any questions about cosmic rays or black holes? Share your thoughts in the comments below!
