In many cases, astronomers have reported dramatic, cataclysmic events, such as the merger of neutron stars or the formation of a black hole; They occur light-years away, usually in another galaxy. Although we can observe their destructive power from the light they emit, their impact on Earth is minimal. However, the relatively recent discovery of certain types of isotopes on the ocean floor indicates that one of these events is occurring quite close to home. And apparently this happened not so long ago.

So how can isotopes on the ocean floor tell if a catastrophic event has recently occurred nearby? As for some elements, very few processes in the universe can create them naturally. Two of these, Fe-60 and Pu-244, were found in ocean sediments dating back 3-4 million years.

Fe-60 could theoretically be created in an ordinary supernova. While these events are still powerful, they are not the universe-shaking catastrophes we can see from afar. However, Pu-244 is believed to only form in these extreme events. Notably, the formation of this plutonium isotope only occurs in certain classes of supernovae, such as kilonovae, or in the merger of at least one neutron star with something else.

Scientists had already looked at the ratio of these two isotopes and determined that the merger of a binary neutron star would not result in the observed data. However, a new paper by physicists at the University of Trento has found that under a given debris ejection pattern and a given slope of the fusion event, the isotope ratio of iron and plutonium can be explained by a phenomenon known as: Formation by the collision of two neutron stars or one neutron star. “kilonova” and a black hole.

An important feature of the data was that these isotopes had not yet decayed. The half-life of Pu-244 is 81 million years, while the half-life of Fe-60 is only 1.5 million years. Combining the known age of the sediment with the current half-lives of these elements allowed scientists to determine the underlying relationship in the paper, which is now hosted on the preprint server. arXiv.

Other papers suggest that different types of rare supernovae may have created the plutonium/iron ratio in the sediment sample. These include events such as magneto-spinning supernovae or collapse; but the document shows that neither can be a source.

So the kilonova remains the most likely source, but what about studies that find it impossible to explain isotope ratios? Several factors play a role in the scenario in which the Kilonova explanation begins to make sense. First, a type of gravitational collapse during the merger creates powerful “spiral wave” winds that eject much more matter from the kilonova.

This gravitational collapse, as well as neutrino bombardment of the ejecta, can create amounts of Pu-244 similar to those found on the ocean floor. The researchers ran a series of simulations proving that such a relationship was possible, but found that it was only possible if the Kilonova was slightly tilted relative to the Earth; this relationship was only significant if the wind from mid- and high-latitudes was as follows. One that crashed into our planet.

So it seems that a kilonova could explain the presence of Fe-60 and Pu-244 in our oceans. And since these isotopes were found in sediments formed 3 to 4 million years ago, it seems likely that the Kilonova formed at that time. But how far was it?

To calculate this, the researchers calculated the different emissions they would expect for each element depending on the wind speed produced by the kilonova. The answer appeared to be around 150-200 parsecs, or about 500-600 light-years away. It’s basically in our backyard, astronomically speaking.

The good news is that this event apparently did not end all life on Earth. And we don’t see any good candidates for such a dramatic event in the next few million years. But studies like this are a reminder that the universe is dangerous, and sometimes dangerous things happen very close to our pale blue dot.