First of all, simulations reveal ghost particles metamorpifying future mergers of neutron stars

New simulations show that neutrino flavor transformations modify both the composition and the signals left after neutron star collisions.

When two neutron stars collide and merge, the result is one of the most energetic events in the universe. These cataclysms generate several types of signals that can be detected from the earth.

New simulations of researchers from Penn State and the University of Tennessee Knoxville show that the way the tiny particles called neutrinos are mixed and change affect both how fusion progresses and what it emits. Neutrinos can travel through large cosmic distances without almost any disturbance, and their behavior shapes the result of the collision.

According to the team, the results speak of longtime issues on the origin of metals and elements of rare land, and they also help scientists to probe physics in extreme environments.

The study, published in Physical examination lettersis the first to model the transformation of the “flavors” of neutrinos during neutron star mergers. Neutrinos are fundamental particles which interact only weakly with matter and appear in three flavors named for the particles they accompany: electron, muon and tau. Under specific conditions, including those within a neutron star, neutrinos can theoretically change flavors, which in turn changes the types of particles with which they interact.

“The previous simulations of binary neutron neutrons mergers have not included the transformation of the flavor of neutrinos,” said Yi Qiu, a student graduated in physics at the Penn State Eberly College of Science and first author of the newspaper. “This is partly due to the fact that this process occurs on a time scale in nanosecond and is very difficult to capture and in part because, until recently, we did not know enough on the theoretical physics underlying these transformations, which is not the standard model of physics. Remnant – as well as the material around it. »»

Build advanced simulations

The researchers have built a computer simulation of a melting of neutron stars from zero, incorporating a variety of physical processes, including gravity, general relativity, hydrodynamics and the mixture of neutrinos. They also explained the transformation of neutrinos of electronic flavor into Muon flavor, which, according to researchers, is the transformation of neutrinos most relevant in this environment. They have modeled several scenarios, varying the timing and the location of the mixture as well as the density of the surrounding material.

The researchers found that all these factors have influenced the composition and structure of the rest of the fusion, including the type and quantities of elements created during the merger. During a collision, neutrons of a neutron star can be launched in other atoms in debris, which can capture neutrons and ultimately decompose in heavier elements, such as heavy metals such as gold and platinum as well as rare earth elements that are used on earth in smartphones, batteries of electric vehicles and other devices.

“The flavor of a neutrino changes the way she interacts with other subjects,” said David Radice, professor of first career in physics and associate professor of astronomy and astrophysics at the Penn State Eberly College of Science and author of the newspaper. “Electronic neutrinos can take a neutron, one of the three basic parts of a atomAnd transform it into the other two, a proton and an electron. But Muon type neutrinos cannot do it. Thus, the conversion of neutrino flavors can modify the number of neutrons available in the system, which has a direct impact on the creation of heavy metals and rare earth elements. There are still many persistent questions about the cosmic origin of these important elements, and we have found that taking into account the neutrino mixture could increase the production of elements by a factor of 10. ”

Earth detectable emissions

The mixture of neutrinos during the fusion also influenced the quantity and composition of the ejected material of the fusion, which, according to the researchers, could modify the detectable emissions of the earth. These emissions generally include gravitational waves – Wave in space – as well as electromagnetic radiation such as X -rays or gamma rays.

“In our simulations, the mixture of neutrinos has had an impact on electromagnetic emissions of neutron star mergers and perhaps also gravitational waves,” said Radice. “With advanced detectors like LigoVirgo and Kagra and their next generation counterparts, such as the Cosmic Explorer Observatory proposed which could start operations in the 2030s, astronomers are ready to detect gravitational waves more often than before. A better understanding of the creation of these programs from neutron star mergers will help us to interpret future observations. »»

The researchers said that the modeling of mixing processes was similar to what a pendulum was upset. Initially, many changes have occurred on an incredibly fast time scale, but ultimately the pendulum settles in a stable balance. But a large part of that, they said, is a hypothesis.

“There are still a lot of things that we do not know about the theoretical physics of these transformations of Neutrinos,” said Qiu. “While the theoretical physics of particles continues to progress, we can considerably improve our simulations. What remains uncertain is where and how these transformations occur in neutron star mergers.

Now that the infrastructure of these complex simulations has been created, the researchers have said that they expect other groups to use technology to continue exploring the impacts of the neutrinos mixture.

“Neutron star mergers work like cosmic laboratories, providing important information on extreme physics that we cannot reproduce safely on earth,” said Radice.

Reference: “Transformation of the flavor of neutrinos in neutron star mergers” by Yi Qiu, David Radice, Sherwood Richers and Maitraya Bhattacharyya, August 26, 2025, Physical examination letters.
Doi: 10.1103 / H2Q7-KN3V

In addition to Qiu and Radice, the research team includes Maitraya Bhattacharyya, a postdoctoral scholarship holder at the Penn State Institute for Gravitation and the Cosmos, and Sherwood Richers at the University of Tennessee, Knoxville. The financing of the American Department of Energy, the Sloan Foundation and the US National Science Foundation supported this work.

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