NASA’s Advanced Composition Explorer (ACE) spacecraft allowed researchers to determine the source of cosmic rays by spotting a very rare particle that dictates how the source of the cosmic ray can be traced from the Earth.
One of the researchers, Eric Christian, commented that “before the ACE observations, we didn’t know if this radiation was created a long time ago and far, far away, or relatively recently and nearby.”
Detecting cosmic rays
The particle found by the ACE’s Cosmic Ray Isotope Spectrometer (CRIS) led researchers to decipher how old the cosmic rays were and how far are they from their source. The particle is known as Iron-60 (60Fe), a radioactive isotope of iron that comes to fruition in supernovas. Massive stars explode and send the 60Fe flying onto space at cosmic ray speed. If a nearby star explodes, then the particles of both stars collide. On the last 17 years, CRIS has been able to detect over 300,000 particles of the most common isotope of iron 56Fe, but it also spotted 15 particles that correspond to 60Fe.
The study was led by Robert Binns and Martin Israel of Washington University, and the team was comprised of NASA, Washington University and Caltech scientists. These findings confirm the hypothesis of a massive star near our galactic location becoming a supernova 2.3 million years ago.
Cosmic rays are comprised of atoms that have been separated from their electrons, leaving only the nucleus of each atom as it is shot through space at near-light speed. Since the nucleus of an atom is comprised of protons and neutrons, it sports a positive charge, which allows the particle’s trajectory to be altered by the magnetic fields found throughout space.
Getting into the source
Researchers determined that the source of the cosmic rays had to be clusters of massive stars, which are known as OB associations. In these clusters, supernova explosions occur every few million years from each other, producing the 60Fe radioactive isotope.
The particles detected by CRIS seem to have been formed and launched by two supernovas exploding 2 million years from each other. It is possible to assert this because the 60Fe isotope decays after 2.6 million years. Previous studies back up the theory that it is necessary for two nearby stars to explode to form cosmic rays, as the first explosion creates the particles and the second one shoots them through space.