Ancient star explosions revealed in the deep sea

nebula
Credit: Pixabay/CC0 Public Domain

A mystery surrounding the space around our solar system is unfolding thanks to evidence of supernovae found in deep-sea sediments.

Professor Anton Wallner, a at ANU, led the study which shows the Earth has been traveling for the last 33,000 years through a cloud of faintly radioactive dust.

"These could be remnants of previous supernova explosions, a powerful and super bright explosion of a star," Professor Wallner said.

Professor Wallner conducted the research at the ANU Heavy Ion Accelerator Facility (HIAF). He also holds joint positions at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and Technical University Dresden (TUD) in Germany.

The researchers searched through several deep-sea sediments from two different locations that date back 33,000 years using the extreme sensitivity of HIAF's mass spectrometer. They found clear traces of the isotope iron-60, which is formed when stars die in supernova explosions.

Iron-60 is radioactive and completely decays away within 15 million years, which means any iron-60 found on the earth must have been formed much later than the rest of the 4.6-billion-year old earth and arrived here from nearby supernovae before settling on the ocean floor.

Professor Wallner previously found traces of iron-60 at about 2.6 million years ago, and possibly another at around 6 million years ago, suggesting earth had traveled through fallout clouds from nearby supernovae.

For the last few thousand years the solar system has been moving through a denser cloud of gas and dust, known as the local interstellar cloud, (LIC), whose origins are unclear. If this cloud had originated during the past few million years from a supernova, it would contain iron-60, and so the team decided to search more recent sediment to find out.

Sure enough, there was iron-60 in the sediment at extremely low levels—equating to radioactivity levels in space far below the Earth's natural background levels—and the distribution of the iron-60 matched earth's recent travel through the local interstellar cloud. But the iron-60 extended further back and was spread throughout the entire 33,000 year measurement period.

The lack of correlation with the 's time in the current local interstellar cloud seems to pose more questions than it answers. Firstly, if the cloud was not formed by a supernova, where did it come from? And secondly, why is there iron-60 so evenly spread throughout space?

"There are recent papers that suggest iron-60 trapped in might bounce around in the interstellar medium," Professor Wallner said.

"So the iron-60 could originate from even older supernovae explosions, and what we measure is some kind of echo. More data is required to resolve these details."

Scientists from ANU, the Australian Nuclear Science and Technology Organization, HZDR, the University of Vienna and the TU Berlin were involved in the study.

The findings have been published in the journal PNAS.


Explore further

Supernovae showered Earth with radioactive debris

More information: A. Wallner et al. 60Fe deposition during the late Pleistocene and the Holocene echoes past supernova activity, Proceedings of the National Academy of Sciences (2020). DOI: 10.1073/pnas.1916769117
Citation: Ancient star explosions revealed in the deep sea (2020, August 25) retrieved 23 September 2021 from https://phys.org/news/2020-08-ancient-star-explosions-revealed-deep.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
238 shares

Feedback to editors