Traces of iron isotope 60Fe in space indicate that a supernova explosion occurred within the last few million years and continues to sprinkle ashes on Earth.
A couple of weeks ago, two studies suggested that a series of supernova explosions showered the Earth with radioactive debris a couple of million years ago. Researchers reached to the conclusion when they found concentrations of isotope of iron 60Fe in the ocean floor. The iron isotope 60Fe is very rare and is created when a massive star collapses in the form of supernova.
Now, researchers at Washington University in St. Louis have found that the showering of radioactive debris is not over yet. The remnants of supernova are still raining onto Earth.
Thanks to the observations of NASA’s Advanced Composition Explorer (ACE) and Cosmic Ray Isotope Spectrometer (CRIS), scientists have been able to detect the iron isotope 60Fe. Though CRIS has tracked down thousands of particles of ordinary iron 56Fe over the past 17 years but the instrument has detected only 15 isotopes of 60Fe. Still they are enough to reveal the origin of cosmic rays.
Cosmic rays are atom nuclei that have been stripped of their electrons and are flying through at high speeds and in every direction. The radioactive isotope said to have a half life of 2.6 million years and must have formed in a relatively nearby supernova within 3.2 and 1.7 million years ago. But scientists have noticed a delay when the nuclei was formed and when it scattered in the space, suggesting that at least one more supernova must have took place nearby and caused to accelerate the process.
“Our detection of radioactive cosmic-ray iron nuclei is a smoking gun indicating that there has been a supernova in the last few million years in our neighborhood of the galaxy.” Robert Binns lead author of the study.
Co-author Martian Israel says. “The new data also show the source of galactic cosmic rays in nearby clusters of massive stars, where supernova explosions occur every few million years.”
Researchers believe that there was a delay of at least 100,000 years between the creation of cosmic rays and their acceleration, which is an indication that a second nearby supernova caused the acceleration and dispersed radiations through the space and onto Earth.
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Cosmic rays were first discovered in 1920s. Ever since, researchers have been intensively studying these energetic particles and trying to understand them more clearly and in detail.