Magnetar

A magnetar is a rare and extreme type of neutron star.

These objects are defined by their incredibly intense magnetic fields. These fields range from approximately 10^9 to 10^11 Tesla. This makes them the most powerful magnetic objects ever detected in the universe. The energy from the decay of these magnetic fields powers the emission of high-energy electromagnetic radiation. This radiation mostly appears as X-rays and gamma rays. Because of this unique energy source, magnetars are vital for understanding high-energy physics in space.

Magnetars form through the dramatic collapse of massive stars. To create one, a star must have a mass between 10 and 25 times that of our Sun. When such a star dies in a supernova, it collapses into a dense neutron star. A magnetar has a mass of about 1.4 solar masses. Despite this mass, its diameter is similar to other neutron stars. The density is staggering. A single tablespoon of magnetar material would weigh over 100 million tons.

There are different ways scientists think these magnetic fields become so strong. One dominant model is the magnetohydrodynamic dynamo process. This occurs in the turbulent, dense, conducting fluid present before the star reaches equilibrium. This process converts heat and rotational energy into magnetic energy. This can boost a field from 10^8 Tesla to over 10^11 Tesla. An alternative model suggests they simply result from the collapse of stars that already had unusually strong magnetic fields. Once formed, these fields may persist due to currents in a proton-superconductor phase deep inside the star.

Magnetars differ from typical neutron stars in several specific ways. First, their magnetic fields are vastly stronger. A magnetar's field is about a trillion times more powerful than Earth's geomagnetic field. Second, they rotate much more slowly. Most observed magnetars rotate only once every two to ten seconds. In contrast, typical radio pulsars can rotate one to ten times every single second.

Their active life is also quite short. After about 10,000 years, the magnetic field decays and the strong X-ray emissions cease.

History shows how our understanding of these stars has grown. In 1992, Robert Duncan and Christopher Thompson proposed the magnetar hypothesis. They wanted to explain transient gamma-ray sources called soft gamma repeaters (SGRs). The theory later helped explain anomalous X-ray pulsars (AXPs). A major breakthrough occurred on March 5, 1979. Several space probes, including Soviet Venera 11 and 12 and NASA's Helios 2, detected a massive gamma-ray blast. This event, named GRB 790305b, was the first observed SGR megaflare. It originated from SGR 0525−66 in the Large Magellanic Cloud.

The physical effects of such magnetism are mind-boggling. At a distance of 1,000 km, the field would be lethal to life. It distorts the electron clouds of atoms, making chemistry impossible. A hydrogen atom at 10^10 Teslas becomes 200 times narrower than its normal diameter. If a magnetar were halfway between the Earth and the Moon, it could wipe the magnetic stripes from every credit card on Earth.

Even the vacuum of space becomes polarized and acts like a calcite crystal.

Scientists have confirmed 24 magnetars, but many more likely exist. Some estimates suggest there are 30 million inactive magnetars in the Milky Way. Notable examples include SGR 1806−20, which is the most magnetized object known. Another, SGR 1900+14, has a surrounding ring of matter 7 light-years across.

In 2020, researchers using the Australian Square Kilometre Array Pathfinder (ASKAP) suggested magnetars might cause fast radio bursts (FRB). This connects these extreme stars to other mysterious signals in our cosmos.