Huge outbursts from quiet magnetars have a surprising source

A quarter-century-old question about the universe’s largest magnetic fields is gaining new attention. These puzzling fields develop around magnetars in a way that was only theorized, until now.

According to Dr. Andrey Igoshev, lead researcher from the University of Leeds, the team’s simulations have settled debates that have lingered for 25 years.

The study was focused on the birth and growth of a neutron star, which is a compact stellar core that remains after a massive star collapses.

What makes magnetars so powerful

A magnetar is a neutron star with a magnetic field that can reach billions of times the strength of what we experience on Earth.

Such wild conditions are known to cause bursts of X-ray radiation that defy simple explanations, leading astronomers to look for clues to explain how these bizarre objects stay so active.

“Magnetars play a special role in modern high-energy astrophysics. They have been suggested as central engines for superluminous supernovae and ultralong γ-ray bursts. They produce at least a fraction of the mysterious fast radio bursts,” noted the researchers.

Some magnetars display dipole fields in a lower range, yet they still show the same dramatic flares. This led experts to question why low-intensity magnetars share striking similarities with those having stronger dipole fields.

Supernova fallout speeds up the star

When a massive star runs out of fuel, it collapses and ejects material outward, leaving behind a tiny, rotating core. A fraction of that matter returns in a process called fallback, and this incoming mass spins the star faster than researchers once expected.

The study revealed that this faster spin plays a serious role in ramping up hidden magnetic structures. This finding links a supernova’s aftermath with a star’s subsequent behavior.

Generation of big magnetic fields

A mechanism called the Tayler-Spruit dynamo involves differential rotation that triggers magnetic instabilities inside the hot, dense interior.

This mechanism was originally proposed years ago, but it had never been fully confirmed as the driver behind certain field configurations.

“Low-intensity magnetars can be produced as a result of a Tayler-Spruit dynamo inside a neutron protostar,” noted Dr. Igoshev. This points to a distinct route for generating big magnetic fields in stars that do not exhibit the classic ultra-strong external dipole signals.

Weak magnetars with powerful bursts

“X-ray observations show that in two cases, low-intensity magnetars have small-scale magnetic fields 10-100 times stronger than their dipole fields,” said Dr. Igoshev.

Observations reveal that certain neutron stars still release bursts just like their mightier relatives. 

Objects such as SGR 0418+5729 and Swift J1882.3-1606 confirm that an external reading of the star’s field doesn’t always match its internal reality. The high-energy flashes seen from these objects demonstrate how less obvious fields can still unleash surprising events.

Quiet stars with huge outbursts

According to the researchers, these findings add context to models of supernova remnants and the huge outbursts that neutron stars sometimes display.

The role of proto-neutron-star dynamos goes beyond standard theories, linking fallback conditions to later phenomena that defy easy explanations.

This approach might also clarify the huge release of energy in certain gamma-ray bursts. Each step forward reveals ways in which intense fields appear or linger, even after a star has seemingly settled down.

Gazing into the future

Upcoming space observatories will provide new data that may help scientists understand how complex magnetic fields form inside magnetars.

These deep magnetic networks play a crucial role in influencing the energy output of these stars, potentially explaining why some magnetars release powerful bursts while others remain quiet.

By improving our ability to map a star’s internal structure, scientists can better predict which magnetars are at risk of producing sudden and intense flares. This could lead to better forecasting of cosmic events that affect space environments.

The research highlights how the conditions immediately following a supernova explosion shape what happens later. The remnants left behind can determine how a star evolves and whether it will exhibit extreme behavior.

Hidden processes within a star’s core might be far more complex than previously thought, pushing scientists to rethink what they know about extreme cosmic events.

The study is published in Nature Astronomy.

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