Approximately a century ago, researchers started to realize that some of the radiation we discover in Earths atmosphere is not local in origin. This ultimately triggered the discovery of cosmic rays, high-energy protons and atomic nuclei that have been removed of their electrons and sped up to relativistic speeds (near to the speed of light). There are still numerous mysteries surrounding this weird (and potentially deadly) phenomenon.
This includes concerns about their origins and how the main element of cosmic rays (protons) are sped up to such high velocity. Thanks to new research study led by the University of Nagoya, researchers have actually quantified the amount of cosmic rays produced in a supernova residue for the very first time. This research has helped solve a 100-year secret and is a significant action towards figuring out exactly where cosmic rays come from.
Thanks to new research led by the University of Nagoya, scientists have quantified the amount of cosmic rays produced in a supernova remnant for the first time. In recent years, enhanced observations have led some researchers to speculate that supernova remnants give rise to cosmic rays due to the fact that the protons they speed up engage with protons in the ISM to create really high-energy (VHE) gamma rays.
Figuring out which source is higher is vital to determining the origin of cosmic rays. They then combined all 3 data sets and determined that protons account for 67 ± 8% of cosmic rays while cosmic-ray electrons account for 33 ± 8%– approximately a 70/30 split. These findings are groundbreaking since they are the first time that the possible origins of cosmic rays have actually been measured.
While scientists theorize that cosmic rays stem from many sources– our Sun, supernovae, gamma-ray bursts (GRBs), and Active Galactic Nuclei ( aka. quasars)– their exact origin has been a mystery since they were first discovered in 1912. Astronomers have thought that supernova residues (the after-effects of supernova surges) are accountable for accelerating them to nearly the speed of light.
When energetic cosmic rays strike the top of the Earths environment, showers of high-energy particles happen. Cosmic rays were discovered suddenly in 1912. Credit: Simon Swordy (U. Chicago), NASA
As they travel through our galaxy, cosmic rays contribute in the chemical evolution of the interstellar medium (ISM). As such, understanding their origin is important to understanding how galaxies evolve. In recent years, improved observations have actually led some scientists to speculate that supernova residues trigger cosmic rays due to the fact that the protons they accelerate communicate with protons in the ISM to develop very high-energy (VHE) gamma rays.
Gamma-rays are likewise produced by electrons that connect with photons in the ISM, which can be in the type of infrared photons or radiation from the Cosmic Microwave Background (CMB). Figuring out which source is greater is vital to determining the origin of cosmic rays. Wishing to clarify this, the research study team– which included members from Nagoya University, the National Astronomical Observatory of Japan ( NAOJ), and the University of Adelaide, Australia– observed the supernova residue RX J1713.7? 3946 (RX J1713).
Cosmic-ray protons interact with interstellar protons such as atomic and molecular hydrogen gas. Cosmic-ray electrons stimulate interstellar photons (primarily Cosmic Microwave Background; CMB) into gamma-ray energy via inverse Compton scattering (leptonic process).
The secret to their research study was the unique technique they established to measure the source of gamma-rays in interstellar area. Previous observations have actually revealed that the strength of VHE gamma-rays caused by protons colliding with other protons in the ISM is proportional to the interstellar gas density, which is discernible using radio-line imaging. On the other hand, gamma-rays triggered by the interaction of electrons with photons in the ISM are likewise expected to be proportional to the intensity of nonthermal X-rays from electrons.
For the sake of their study, the team relied on information acquired by the High Energy Stereoscopic System (HESS), a VHE gamma-ray observatory situated in Namibia (and operated by the Max Planck Institute for Nuclear Physics). They then combined this with X-ray data acquired by the ESAs X-ray Multi-Mirror Mission (XMM-Newton) observatory and information on the circulation of gas in the interstellar medium.
Maps of gamma-ray strength Ng, interstellar gas density Np, and X-ray strength Nx. Credit: Astrophysics Laboratory, Nagoya University
They then integrated all 3 data sets and figured out that protons account for 67 ± 8% of cosmic rays while cosmic-ray electrons represent 33 ± 8%– roughly a 70/30 split. These findings are groundbreaking because they are the very first time that the possible origins of cosmic rays have actually been measured. They also make up the most conclusive proof to date that supernova residues are the source of cosmic rays.
These outcomes likewise show that gamma-rays from protons are more common in gas-rich interstellar regions, whereas those caused by electrons are enhanced in the gas-poor regions. This supports what numerous researchers have actually predicted, which is that the 2 mechanisms work together to influence the evolution of the ISM. Said Emeritus Professor Yasuo Fukui, who was the research studys lead author:
” This unique approach could not have been accomplished without worldwide partnerships. [It] will be applied to more supernova remnants utilizing the next-generation gamma-ray telescope CTA (Cherenkov Telescope Array) in addition to the existing observatories, which will significantly advance the study of the origin of cosmic rays.”
In addition to leading this project, Fukui has actually been working to measure interstellar gas circulation since 2003 utilizing the NANTEN radio telescope at the Las Campanas Observatory in Chile and the Australia Telescope Compact Array. Thanks to Professor Gavin Rowell and Dr. Sabrina Einecke of the University of Adelaide (co-authors on the research study) and the H.E.S.S. team, the spatial resolution and sensitivity of gamma-ray observatories has finally reached the point where it is possible to draw comparisons in between the 2.
Co-author Dr. Hidetoshi Sano of the NAOJ led the analysis of archival datasets from the XMM-Newton observatory. In this respect, this research study also reveals how global cooperations and data-sharing are enabling all type of innovative research. Together with improved instruments, improved approaches and higher chances for cooperation are leading to an age where astronomical advancements are ending up being a routine incident!
Originally released on Universe Today.
For more on this discovery, see Unveiling a 100-Year-Old Astrophysics Mystery: Where the Milky Ways Cosmic Rays Come From.
Reference: “Pursuing the Origin of the Gamma Rays in RX J1713.7-3946 Quantifying the Hadronic and Leptonic Components” by Yasuo Fukui, Hidetoshi Sano, Yumiko Yamane, Takahiro Hayakawa, Tsuyoshi Inoue, Kengo Tachihara, Gavin Rowell and Sabrina Einecke, 9 July 2021, Astrophysical Journal.DOI: 10.3847/ 1538-4357/ abff4a.