Magnetar
Introduction
A Magnetar is a type of neutron star believed to have an extremely powerful magnetic field (∼10^9 to 10^11 T, ∼10^13 to 10^15 G). The magnetic field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays. The theory regarding these objects was proposed by Robert Duncan and Christopher Thompson in 1992, but the first recorded burst of high-energy radiation thought to have been from a magnetar had been detected on March 5, 1979. Subsequent to Duncan and Thompson's work, magnetars have been the subject of intense study, confirmed by observations of the Soft Gamma Repeater (SGR) and Anomalous X-ray Pulsar (AXP) phenomena.
Physical Properties
Magnetars are characterized by their extremely powerful magnetic fields, which can often reach the quantum mechanical limit known as the quantum electrodynamics (QED) limit. These magnetic fields are hundreds of millions of times stronger than any man-made magnet, and quadrillions of times more powerful than the field surrounding Earth. Magnetars also rotate rapidly, with most known examples completing a rotation once every one to ten seconds.
Formation
Magnetars are formed from the supernova explosions of massive stars. The exact process of magnetar formation is not well understood, but it is thought to involve the amplification of the star's magnetic field during the supernova explosion. This process, known as a magnetohydrodynamic dynamo, can result in a neutron star with an ultra-strong magnetic field.
Emission of High-Energy Radiation
The decay of the magnetic field in a magnetar leads to the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays. This radiation can be observed from Earth when the magnetar undergoes a starquake as a result of the magnetic field reconfiguring itself. These starquakes can release more energy in a tenth of a second than our Sun does in 100,000 years.
Observations and Known Magnetars
As of 2021, about 30 magnetars are known, with six of them located in the Milky Way galaxy. The first detected magnetar, SGR 1900+14, was located in 1998. The most recent, Swift J1818.0-1607, was discovered in March 2020. Observations of these objects have been made in X-ray, gamma ray, and more recently in radio wavelengths.
Magnetars and Fast Radio Bursts
There is a growing consensus among astronomers that magnetars are the most likely source of the mysterious Fast Radio Bursts (FRBs) that have been detected from distant galaxies. This theory was strengthened in 2020 when a magnetar in our own galaxy emitted a radio burst that was similar in many ways to the extragalactic FRBs.