A magnetar is an exotic type of neutron star, its defining feature that it has an ultra-powerful magnetic field. The field is about 1,000 times stronger than a normal neutron star and about a trillion times stronger than the Earth's. Magnetars are, by far, the most magnetic stars in the universe. A magnetar is a type of neutron star believed to have an extremely powerful magnetic field. 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 in 1992 by Robert Duncan and Christopher Thompson. Like other neutron stars, magnetars are around 20 kilometres (12 mi) in diameter, and have a mass about 1.4 solar masses. They are formed by the collapse of a star with a mass 10–25 times that of the Sun. To have such large magnetic fields, magnetars are thought to originate from the supernova of very massive stars. Gaensler and his colleagues have found evidence for this in an enormous void - more than 70 light-years across - that showed up in their radio data. Only about a dozen magnetars have been discovered so far. These appear to be a special breed of neutron stars, which themselves are well known for their strong magnetic fields.Magnetars are characterized by their extremely powerful magnetic fields of 100 million to 100 billion tesla. 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. The tesla is a derived unit of the magnetic B-field strength in the International System of Units. One tesla is equal to one weber per square metre. Rarely, magnetars produce enormous eruptions called giant flares that produce gamma rays, the highest-energy form of light. Most of the 29 magnetars now cataloged in our Milky Way galaxy exhibit occasional X-ray activity, but only two have produced giant flares. The "magnetar," or magnetic neutron star known as Soft Gamma Repeater 1806-20, is the most powerful known magnetic object in the universe. When a massive star collapses under its own gravity during a supernova explosion, it forms either a neutron star or black hole. Magnetars are an unusual and exotic form of neutron star. The magnetar is located close to the plane of the Milky Way galaxy at a distance of about 21,000 light-years from Earth. Other astronomers have also observed J1818. 0-1607 with radio telescopes, such as the NSF's Karl Jansky Very Large Array (VLA), and determined that it gives off radio waves. At just 500 years old and spinning at 1.4 rotations per second, this magnetic neutron star is even more exotic than previously thought. Magnetars are highly magnetic neutron stars, which, in turn, are dense supernovae remnants.

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