Scientists discover a star-neutron collision that could have created plutonium in our solar system

In 2017, observatories around the world observed a high-energy collision between a pair of dense objects, each slightly larger than the Sun but only the size of a city. A similar collision closer to home could have produced some of the heaviest elements of our own solar system – and scientists think they know when.

Scientists now believe that these binary neutron star fusions are an important source of heavier elements than iron in the universe. These elements are rare, but they are also among the most important elements for us, human beings. With the help of measurements of what remains of these elements in ancient meteorites, two researchers worked back to locate the fusion of neutron stars that produced some of them.

"We discovered this fusion of binary stars two years ago and it was close to the Milky Way – much closer than expected," said Gizmodo Imre Bartos, first author of the study and a professor. Assistant at the University of Florida. "We asked if something even closer could have a significant impact on the appearance of the solar system today.

The elements heavier than iron are formed in part by the "process r", where a high energy event causes the rapid removal of many neutrons by the atomic nuclei of the seed. Once the event slows down, some of these neutrons disintegrate radioactively into protons. Stellar explosions called supernovae and neutron star fusion have both been implicated as potential sources of the elements of process r.

The researchers first investigated whether neutron star fusions or supernovae produced the elements that interested them, mainly curium and plutonium. Supernovae, in which stars explode, are relatively common, while neutron stars only fuse a few times every million years in our galaxy, according to the article published in Nature. This means that, if you look back in the past, the abundance of these elements should increase if they were produced by neutron stars, or remain relatively constant if they were produced by supernovae.

Plutonium and curium are radioactive and break down into more stable elements. When the first meteorites were formed, they captured some of these elements, which then decomposed into more stable elements. The relative abundances of decay products in these meteorites allow scientists to go back and determine the approximate age of formation of the initial elements.

When Szosbocs Marka, professor at Columbia University and Bartos, made calculations on the data previously collected from these meteorites, they found that the abundance of these elements reached about 80 million years before the formation of the solar system , while it was only a cloud of gas and dust. He deduced that a single event, probably a fusion of neutron stars a thousand light-years away from the planet, produced the lion's share of curium and perhaps a third of the plutonium of the solar system. This is only a fraction of one percent of the total amount of process-r elements in the solar system, but "there have been a lot of neutron star mergers. in the history of the Milky Way, "said Bartos.

It's a good search. "[These elements] David Helfand, astronomer and professor at Columbia University, told Gizmodo that this is only a tiny fraction of 1% of the universe, but they are very useful to us in many ways. "Just knowing where they come from helps us feel a little more comfortable in the universe."

It is important to note that these results are based on the modeling of indirect measurements and that our knowledge of neutron star collisions and the r process comes from a single experimental observation. Although unlikely, perhaps another type of even more chaotic, high-energy event has produced these elements. Bartos explained to Gizmodo that the next step was to measure more elements with unknown abundances, to create better simulations and, of course, to observe more neutron star collisions. Fortunately, the LIGO and Virgo gravitational wave observatories have been upgraded and have already begun to detect signals from colliding black holes and possibly even some neutron stars.

Bartos was excited about how these results combine so many different fields, from Earth sciences to astrophysics, to chemistry. "By linking this area to this particular work, we hope that we will make a greater effort to use this information in unison."