麻豆淫院

Binary neutron star mergers, cosmic collisions between two very dense stellar remnants made up predominantly of neutrons, have been the topic of numerous astrophysics studies due to their fascinating underlying physics and their possible cosmological outcomes. Most previous studies aimed at simulating and better understanding these events relied on computational methods designed to solve Einstein's equations of general relativity under extreme conditions, such as those that would be present during neutron star mergers.

Researchers at the Max Planck Institute for Gravitational 麻豆淫院ics (Albert Einstein Institute), Yukawa Institute for Theoretical 麻豆淫院ics, Chiba University, and Toho University recently performed the longest simulation of binary neutron star mergers to date, utilizing a framework for modeling the interactions between magnetic fields, high-density matter and neutrinos, known as the neutrino-radiation magnetohydrodynamics (MHD) framework.

Their , outlined in 麻豆淫院ical Review Letters, reveals the emergence of a magnetically dominated jet from the merger, followed by the collapse of the binary neutron star system into a black hole.

"In 2019, the gravitational wave detectors detected an event that originated from a binary neutron star merger that collapsed to a black hole right after the merger," Kota Hayashi, first author of the paper, told 麻豆淫院. "This work aims to clarify the merger and post-merger dynamics of such a promptly collapsing merger and predict multi-messenger signals (gravitational wave, electromagnetic emissions, neutrino emissions) from a foreseen event."

The merger simulated by Hayashi and his colleagues is between two neutron stars of different masses, one of 1.25 and the other of 1.65 solar masses. Their simulation was rooted in the so-called SFHo equation of state, a mathematical model that describes how matter behaves under extreme conditions (e.g., at extreme temperatures, densities and pressures), such as those inside neutron stars.

"We performed a simulation that includes the evolution of the gravitational field, neutrino radiation, magnetic field, and hydrodynamics," explained Hayashi. "All these effects play crucial roles in the system. We evolved the system up to a record-breaking 1.5 seconds of real time by using the Japanese supercomputer Fugaku."

The researchers observed that following its merger, the binary neutron star system they simulated promptly collapsed into a black hole, surrounded by a turbulent accretion disk, a rotating disk-shaped structure. As it is driven by a magneto-rotational instability, this disk contributes to the ejection of mass and produces a so-called Poynting flux (i.e., an outflow of energy carried by electromagnetic fields). This culminated in the emergence of a magnetically driven jet with a luminosity equivalent to around 10鈦粹伖 erg/s along the spin axis of the black hole.

"This is the first work to discover the launch of the magnetically driven jet from a binary neutron star merger that collapsed to a black hole right after the merger," said Hayashi.

"It shows that this kind of system can drive a gamma-ray burst, the most energetic explosion event in the universe. We clarified that the magnetic field that drives the jet is generated in the post-merger accretion disk through a mechanism called dynamo."

The simulation run by Hayashi and his colleagues sheds new light on the complex physics of binary neutron star mergers, showing that when these mergers are followed by the formation of black holes, they could also lead to the emergence of a magnetically dominated jet. In the future, it could help to improve existing astrophysical theories, potentially linking models of neutron star mergers with those describing the production of gamma-ray bursts (i.e., short-lived explosions of high energy radiation with very short wavelengths).

"This study mainly focused only on the dynamics of the merger, mass ejection, and jet launch," added Hayashi. "Further detailed research focusing on the electromagnetic emissions based on this simulation is needed to interpret the foreseen observations.

"Moreover, the acceleration of the jet, which is more than 99.9% of the speed of light, is implied from the observation of gamma-ray bursts and is not captured in the current simulation. Future studies to clarify the acceleration process are needed to fully understand the gamma-ray burst."

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