Magnetars are a class of neutron stars with the most powerful magnetic fields in the universe. These extremely dense objects are at the center of extreme cosmic phenomena such as hypernovae, fast radio bursts, and gamma-ray emissions. However, their exact nature remains shrouded in mystery. An international research team, including Geneva University, has for the first time reproduced the formation and evolution of magnetars using numerical simulations. This groundbreaking work, published in the journal Natural astronomy, represents a significant leap in our understanding of these celestial bodies.

At the end of their lives, stars with a mass of eight times the sun experience a core collapse due to gravity. This event marks the beginning of a supernova explosion: the outer layer is ejected, while the core contracts violently, forming a neutron star, the most dense known object in the universe. A teaspoon of the material would weigh one billion tons, or approximately 100,000 Eiffel Towers!

While neutron stars are typically observed emitting radio waves, some emit intense X-ray bursts and gamma rays. They are generally called ‘magnetars’ because their emissions are thought to be caused by the dissipation of an extremely intense magnetic field, one million billion times stronger than Earth’s!

The Mystery of Magnetars

The intense magnetic field of magnetars plays a crucial role in the radiation phenomena associated with them. Scientists are working to understand the origin of these magnetic fields. Some theories have been proposed but one shows the generation of magnetic fields through dynamo actions in proto-neutron stars, a few seconds after the explosion begins.

Dynamo action allows conductive fluids, such as plasma, with fairly complex motions, to strengthen and maintain their own magnetic field against the diffusive effect, which weakens it. This amplification effect is undoubtedly the origin of most astrophysical magnetic fields. Unlike others, this theory is supported by a large number of numerical simulations,

The neutron star simulated in this study reproduces the observational characteristics of what is called the Magnatar Medan is weak.

New Magnetar Formation Scenario

For many dynamo actions to be effective, it requires rapid rotation of the progenitor star core, but the mystery is not completely understood. Paul Barreres and researchers Jerome Guilet and Raphael Raynaud from the Astrophysics Department in CEA Saclay have studied alternative hypotheses.

this shows that proto-neutron stars are rapidly rotated by several fragments that were originally ejected during the Supernova, and then fell to the surface of the stars. “This makes our new formation scenario independent of the rotation of the ancestral stars.”

Paul Barrerré said.

The preferred mechanism to strengthen the magnetic field in this proto-neutron star is a certain type of dynamo, popularly known as Tayler-Spruit dynamical mechanism, this mechanism feeds the differences in rotation in stars and instability of the magnetic field. Dynamo is famous by researchers studying stars, because it can explain the core rotation of stars, said the researcher.

Magnetar Evolution Simulation

Apart from its relevance, this newly discovered scenario focuses on the very initial moments after the Supernova. This research cross-collaborates with scientists from the University of Newcastle and Leeds, where they specialized in the evolution of neutron stars, and produced the first numerical simulation of evolution, on a scale of a million years, within the neutron star which displays the initial complex magnetic field which had been produced by the Dynamo Tayler-Spruit.

“The combination of our expertise, for the first time, bridges the gap between our research on the formation of Proto-Neutron stars and evolutionary research considering developing neutron stars “said Paul Barrère.

The neutron star simulated in this study reproduces the observational characteristics of what is called weak field Magnetar discovered in 2010, this sort of magnetar has a magnetic dipole ten to one hundred times weaker than a standard magnetar. This study shows that these magnetars might be formed by the protostar neutron which is accelerated by the increase in Supernova material and where the Tayler-Spruit dynamo operates.

“Our work marks a significant milestone in our understanding of Magnetars and sheds a new, fascinating light on the study of other dynamo effects. Our findings demonstrate that each dynamo leaves its footprint in a complex magnetic field configuration, and therefore in the emission patterns observed from Magnetars. While the Dynamo Tayler-Pruit is associated with Low Medan Magnetar, we aspire to identify in the future, mechanisms related to other Magnetars.” Paul Barrère concluded.