Extragalactic cosmic ray Extragalactic cosmic ray 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 10 eV. 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
NASA/IPAC Extragalactic Database entered to the extent possible, and some basic data collected. Bibliographic references relevant to individual objects have been compiled, and abstracts of extragalactic interest are kept on line. Detailed and referenced photometry, position, and redshift data, have been taken from large compilations and from the literature. NED also includes images from 2MASS, from the literature, and from the Digitized Sky Survey. As of March 2014, NED contains 206 million distinct astronomical objects with 232 million cross-identifications across multiple wavelengths, with redshift measurements for 5 million objects, 1.9 billion photometric data points, 609 million diameter measurements, 71 thousand redshift-independent distances for