page_title: Extragalactic cosmic ray
section_title: Origin
hierarchical_section_title: Extragalactic cosmic ray / Origin
caption_attribution_description: English: The jet emerging from the galactic core of M87 (NGC 4486). The jet extends to about 20 arc seconds (absolute length ca. 5 kly). Composite image of Hubble Telescope observations. The galaxy is too distant for the Hubble Telescope to resolve individual stars; the bright dots in the image are star clusters, assumed to contain some hundreds of thousands of stars each. Original caption: "Black Hole-Powered Jet of Electrons and Sub-Atomic Particles Streams From Center of Galaxy M87" The data used in this image was collected with Hubble's Wide Field Planetary Camera 2 in 1998 by J.A. Biretta, W.B. Sparks, F.D. Macchetto, and E.S. Perlman (STScI). This composite image was compiled by the Hubble Heritage team based on these exposures of ultraviolet, blue, green, and infrared light. Čeština: Výtrysk plazmatu z jádra galaxie M87, který vychází z okolí černé díry
context_page_description: Extragalactic cosmic rays are very-high-energy particles that flow into the Solar System from beyond the Milky Way galaxy. The energies these particles possess are in excess of 10¹⁵ eV.
context_section_description: Unlike solar or galactic cosmic rays, little is known about the origins of extragalactic cosmic rays. This is largely due to a lack of statistics: only about 1 extragalactic cosmic ray particle per square meter per year reaches the Earth's surface (see figure).
  There are many ideas about which processes may be responsible for cosmic rays with such high energies. In the 'bottom-up' approach, cosmic rays gain more and more energy through electromagnetic processes. Bouncing randomly back and forth in the shock waves of some violent object allows some of the particles to gain energy. Eventually they may build up enough speed that the object can no longer contain them, and they escape. Proposed sites for this type of acceleration include gamma ray bursts and active galactic nuclei. Indeed, recent analysis of cosmic ray measurements with the Pierre Auger Observatory suggests a correlation between the arrival directions of cosmic rays of the highest energies of more than 5×10¹⁹ eV and the positions of nearby active galaxies.
  There are many more possible sources scientists are considering. These include colliding galaxy systems, accretion flow shocks to clusters of galaxies, and more exotic processes from the very early universe, such as the decay of superheavy particles trapped in the galactic halo, or topological defects.
caption: Image of an active galactic nucleus of the active galaxy M87.
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