Magnetars: The Strongest Known Magnets

Somewhere in our galaxy right now, an object the size of a city is generating a magnetic field a trillion times stronger than anything on Earth.

What are Magnetars?

Magnetars are a specific type of neutron stars. Just like usual neutron stars, they are relatively small and extremely dense. What differentiates them is an even stronger magnetic field. A magnetar's field strength could be around 10¹⁵ Gauss. For comparison, a fridge magnet would be around 100 Gauss. Being the most powerful magnets in the observable universe, they can also stretch atoms around them into long cylinders.

Another difference between regular neutron stars and magnetars is that the latter spins much more slowly: a neutron star may spin up to hundreds of times a second whereas a magnetar would spin once every two to twelve seconds.

How are Magnetars formed?

The formation of a magnetar starts just like any other neutron star. A dying star eventually cannot perform nuclear fusion to remain stable, so it collapses under its own gravity and star dust expels out in an explosion called the supernova. A small dense core is left behind and this is a regular neutron star. How exactly a Magnetar’s magnetic field forms is still an open question, and several mechanisms have been proposed. The leading idea is that during the first seconds of the neutron star’s life, hot material creates convection currents which, paired with high speed spinning, cause charged particles to twist and amplify the star’s existing magnetic field — a process known as a dynamo. As a result, the field gets stronger. Exactly which type of dynamo is responsible may vary from magnetar to magnetar, and research is ongoing.

How many magnetars have been found?

The first found magnetar was SGR 0526−66, in the Large Magellanic Cloud, located about 163,000 light-years from Earth. This was significant and opened a brand new branch of study for physicists across the globe. Another such important magnetar is SGR 1806−20, estimated to be between 28,000 and 50,000 light-years from Earth in the constellation of Sagittarius, and is the most magnetized object known. In total, only around 30 magnetars have been confirmed or identified as candidates so far, making them a rare find.

Why are magnetars important?

For decades, scientists had been observing unexplained Fast Radio Bursts (FRBs). Since the discovery of magnetars, they are now a confirmed source of FRBs. The clearest proof of this came in April 2020, when astronomers detected an FRB originating from SGR 1935+2154, a magnetar within our own galaxy. It was the first time an FRB had been traced back to a known source, finally confirming what scientists had long suspected. Alongside this, they are also perfect to study matter under extreme conditions, like high magnetism, which cannot be replicated on earth.

Magnetars remind us that no matter how extreme the physics gets; nature always finds a way to go further.