Earth interacted with supernova remnants for one million years
As the group of Prof. Shawn Bishop could show, the supernova signal was first detectable at a time starting about 2.7 Million years ago. According to the researcher's analyses, our solar system spent one Million years to transit trough the remnants of a supernova.
When massive stars with more than ten solar masses have, at the end of their evolution, consumed all of their nuclear fuel supply, they collapse under their gravity and terminate in so-called core-collapse supernovae.
Thereby they eject huge amounts of matter into their surroundings. If a supernova occurs sufficiently close to our solar system, it should leave traces of supernova debris on Earth, in the form of specific radioisotopes.
Among the elemental species known to be produced in these stars, the radioisotope Fe-60 stands out: This radioisotope has no natural, terrestrial production mechanisms; thus, a detection of Fe-60 atoms within terrestrial reservoirs is proof for the direct deposition of supernova material within our solar system.
An excess of Fe-60 was already observed in around two million year old layers of a ferromanganese (FeMn) crust retrieved from the Pacific Ocean and, most recently, in lunar samples. These Fe-60 signals have been attributed to depositions of supernova ejecta.
However, due to the slow growth rate of the FeMn crust, the Fe-60 signal had a poor temporal resolution; while lunar regolith cannot record time information because sedimentation does not occur on the moon.
Now for the first time, physicists of the group of Shawn Bishop, TUM Professor on Nuclear Astrophysics, succeeded in discovering a time-resolved supernova signal in Earth's microfossil record, residing in biogenically produced crystals from two Pacific Ocean sediment drill cores.
The onset of the Fe-60 signal occurs at around 2.7 Million years and is centered at around 2.2 Million years. The signal significantly ends around 1.7 Million years.
"Obviously, the solar system spent one Million years to transit through the debris of a supernova," says Shawn Bishop, who is also a principal investigator at the Excellence Cluster Universe. ■