Solving a 100-Year Mystery: Astronomers Locate Source of High-Energy Cosmic Rays

Roughly a century in the past, scientists started to understand that among the radiation we detect in Earth’s ambiance just isn’t native in origin. This ultimately gave rise to the invention of cosmic rays, high-energy protons and atomic nuclei which have been stripped of their electrons and accelerated to relativistic speeds (near the pace of sunshine). Nevertheless, there are nonetheless a number of mysteries surrounding this unusual (and probably deadly) phenomenon.

This contains questions on their origins and the way the primary part of cosmic rays (protons) are accelerated to such excessive velocity. Because of new analysis led by the College of Nagoya, scientists have quantified the quantity of cosmic rays produced in a supernova remnant for the primary time. This analysis has helped resolve a 100-year thriller and is a serious step in direction of figuring out exactly the place cosmic rays come from.

Whereas scientists theorize that cosmic rays originate from many sources – our Solar, supernovae, gamma-ray bursts (GRBs), and Lively Galactic Nuclei (aka. quasars) – their actual origin has been a thriller since they had been first found in 1912. Equally, astronomers have theorized that supernova remnants (the after-effects of supernova explosions) are liable for accelerating them to just about the pace of sunshine.

Showers of High-Energy Particles

Showers of high-energy particles happen when energetic cosmic rays strike the highest of the Earth’s ambiance. Cosmic rays had been found unexpectedly in 1912. Credit score: Simon Swordy (U. Chicago), NASA

As they journey by our galaxy, cosmic rays play a job within the chemical evolution of the interstellar medium (ISM). As such, understanding their origin is vital to understanding how galaxies evolve. Lately, improved observations have led some scientists to invest that supernova remnants give rise to cosmic rays as a result of the protons they speed up work together with protons within the ISM to create very high-energy (VHE) gamma rays.

Nevertheless, gamma-rays are additionally produced by electrons that work together with photons within the ISM, which could be within the type of infrared photons or radiation from the Cosmic Microwave Background (CMB). Subsequently, figuring out which supply is bigger is paramount to figuring out the origin of cosmic rays. Hoping to make clear this, the analysis workforce – which included members from Nagoya College, the Nationwide Astronomical Observatory of Japan (NAOJ), and the College of Adelaide, Australia – noticed the supernova remnant RX J1713.7?3946 (RX J1713).

Schematic Images of Gamma-Ray Production

Schematic photos of gamma-ray manufacturing from cosmic-ray protons and electrons. Cosmic-ray protons work together with interstellar protons corresponding to molecular and atomic hydrogen fuel. The interplay creates impartial pion that shortly decays into two gamma-ray photons (hadronic course of). Cosmic-ray electrons energize interstellar photons (primarily Cosmic Microwave Background; CMB) into gamma-ray power through inverse Compton scattering (leptonic course of). Credit score: Astrophysics Laboratory, Nagoya College

The important thing to their analysis was the novel method they developed to quantify the supply of gamma-rays in interstellar area. Previous observations have proven that the depth of VHE gamma-rays brought on by protons colliding with different protons within the ISM is proportional to the interstellar fuel density, which is discernible utilizing radio-line imaging. Then again, gamma-rays brought on by the interplay of electrons with photons within the ISM are additionally anticipated to be proportional to the depth of nonthermal X-rays from electrons.

For the sake of their examine, the workforce relied on knowledge obtained by the Excessive Power Stereoscopic System (HESS), a VHE gamma-ray observatory positioned in Namibia (and operated by the Max Planck Institute for Nuclear Physics). They then mixed this with X-ray knowledge obtained by the ESA’s X-ray Multi-Mirror Mission (XMM-Newton) observatory and knowledge on the distribution of fuel within the interstellar medium.

Gamma-Ray, Interstellar Gas, and X-Ray Intensity

Maps of gamma-ray depth Ng, interstellar fuel density Np, and X-ray depth Nx. Credit score: Astrophysics Laboratory, Nagoya College

They then mixed all three knowledge units and decided that protons account for 67 ± 8% of cosmic rays whereas cosmic-ray electrons account for 33 ± 8% – roughly a 70/30 break up. These findings are groundbreaking since they’re the primary time that the doable origins of cosmic rays have been quantified. In addition they represent probably the most definitive proof thus far that supernova remnants are the supply of cosmic rays.

These outcomes additionally reveal that gamma-rays from protons are extra frequent in gas-rich interstellar areas, whereas these brought on by electrons are enhanced within the gas-poor areas. This helps what many researchers have predicted, which is that the 2 mechanisms work collectively to affect the evolution of the ISM. Said Emeritus Professor Yasuo Fukui, who was the examine’s lead writer:

“This novel methodology couldn’t have been achieved with out worldwide collaborations. [It] will likely be utilized to extra supernova remnants utilizing the next-generation gamma-ray telescope CTA (Cherenkov Telescope Array) along with the prevailing observatories, which can drastically advance the examine of the origin of cosmic rays.”

Along with main this mission, Fukui has been working to quantify interstellar fuel distribution since 2003 utilizing the NANTEN radio telescope on the Las Campanas Observatory in Chile and the Australia Telescope Compact Array. Because of Professor Gavin Rowell and Dr. Sabrina Einecke of the College of Adelaide (co-authors on the examine) and the H.E.S.S. workforce, the spatial decision and sensitivity of gamma-ray observatories has lastly reached the purpose the place it’s doable to attract comparisons between the 2.

In the meantime, co-author Dr. Hidetoshi Sano of the NAOJ led the evaluation of archival datasets from the XMM-Newton observatory. On this respect, this examine additionally reveals how worldwide collaborations and data-sharing are enabling every kind of cutting-edge analysis. Together with improved devices, improved strategies and larger alternatives for cooperation are resulting in an age the place astronomical breakthroughs have gotten a daily prevalence!

Initially revealed on Universe Today.

For extra on this discovery, see Unveiling a 100-Year-Old Astrophysics Mystery: Where the Milky Way’s Cosmic Rays Come From.

Reference: “Pursuing the Origin of the Gamma Rays in RX J1713.7-3946 Quantifying the Hadronic and Leptonic Elements” 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

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