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A team of researchers from Germany, Austria and Australia has discovered traces of the radioactive isotope iron 60, a true signature of a supernova explosion, in fresh snow in the Antarctic.
Kohnen station in Antarctica. Image credit: Sepp Kipfstuhl.
Iron-60 (60Fe) is a radioactive isotope of iron. It is produced from pre-existing stable iron isotopes by a process called "neutron capture" in massive star layers where helium and carbon atoms are being melted.
This isotope is only expelled into space when the massive star explodes at the end of its life. It then decays with a half-life of 2.6 million years.
Twenty years ago, scientists discovered iron 60 in samples of sediments and crusts taken from the Pacific, Atlantic and Indian Oceans.
More recently, they detected the rare isotope in lunar samples collected by Apollo missions 12, 15 and 16.
"We were wondering where we could possibly find other iron deposits 60 from stellar explosions in the past because the solar system is going through a denser interstellar environment," said Dr. Dominik. Koll, lead author, of the Australian National University and his colleagues.
"It was a difficult undertaking because the fine dust of the cosmos is usually lost in nature."
"We thought, however, that it would be possible to detect dust in the pure Antarctic snow. So we took out our shovels and shoveled the snow.
Interpretation of an explosion of a supernova by an artist. Image Credit: NASA ESA / Hubble / L. Calcada / Goddard Space Flight Center.
Using accelerator mass spectrometry, researchers analyzed 500 kg of snow from the Kohnen station, a container complex in Antarctica.
After extensive analysis, they found at least five iron atoms 60 in their samples.
"We have been able to exclude that these atoms occurred during nuclear weapons tests or as a result of the accident of a reactor in Fukushima, for example," they said. .
"Radioactive isotopes must come from distant stellar explosions."
"However, this iron 60 did not sink on Earth millions of years ago, because the snow collected was not more than 20 years old," they added.
"This does not seem to come from distant supernovae, because otherwise iron dust 60 would have been too depleted in the universe."
Illustration of the solar neighborhood and nearby interstellar clouds over a distance of about 33 light-years. The solar system is located within the local interstellar cloud and near the G-Cloud, which are integrated with the larger local bubble, with a diameter of about 330 light-years. Image Credit: Goddard / Adler Space Center / University of Chicago / Wesleyan NASA.
Dr. Koll and his co-authors suspect that the 60-Antarctic iron came from one of the interstellar dust clouds in the solar neighborhood.
"The closest to Earth is known as the local interstellar cloud, which could have been created by a supernovae," they said.
"Our solar system has entered this cloud, also known as Local Fluff, about 40,000 years ago and will leave it in a few thousand years," said Dr. Gunther Korschinek, researcher at the Technische Universität München and at Excellence. Cluster universe.
"Following this hypothesis, ice core materials over 40,000 years old should not contain any interstellar iron," 60 Dr. Koll added.
"It would be ideal, of course, if we could find evidence of the transition from the solar system to this cloud."
The results were published online in the journal Letters of physical examination.
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Dominik Koll et al. 2019. Interstellar 60Fe in Antarctica. Phys. Rev. Lett 123 (7); doi: 10.1103 / PhysRevLett.123.072701
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