Magnetic | by Brian Koberlein

Raphaël Raynaud (LMPA/AIM/IRFU/DRF/CEA Saclay)

Neutron stars are stellar remnants. Composed of dense nuclear materials, all of them have robust magnetic fields. However the magnetic fields of some neutron stars generally is a thousand instances stronger. They’re referred to as magnetars, and we aren’t fully positive how they generated such highly effective magnetic fields. However a brand new examine in Nature Astronomy reveals some clues.

The overall thought has been that magnetars create their fields via some kind of dynamo course of. That is the place a circulate of magnetic materials generates a magnetic subject. For the reason that circulate is pushed by warmth convection, it may well energy robust fields. Earth’s magnetic subject is unusually robust for a planet of its dimension and is powered by the convection of iron in its core. Nonetheless, the core of a neutron star is made from nucleons, not atoms, so it’s troublesome to find out a selected dynamo course of for magnetars.

For this examine, the crew wished to grasp what are referred to as low-field magnetars. These are magnetars which have weaker magnetic fields than most magnetars, however nonetheless generate bursts of X-rays and gamma rays. Most magnetars are recognized by their high-energy emissions, because it takes intense magnetic fields to create such highly effective bursts. Low-field magnetars shouldn’t have a robust sufficient subject to create such bursts, however they often do. This could counsel that at instances their magnetic fields change into intense. The query is how.

To reply this query, the crew ran pc simulations of a number of dynamo fashions, searching for one which finest match the observational knowledge. They discovered that one of the best match concerned what’s referred to as the Tayler–Spruit dynamo. This dynamo is well-known in stellar fashions and includes the differential rotation of a stellar core. Stars don’t rotate as a single inflexible object. As an alternative, totally different latitudes of a star rotate at barely totally different charges. That is doubtless attributable to a fast-rotating core, which might produce the Tayler–Spruit dynamo.

The authors demonstrated that as a low-field magnetar kinds, the supernova that created the magnetar transfers angular momentum to its core, thus making a differential rotation. Via the Tayler–Spruit dynamo, this could create bursts of intense magnetic fields that energy the X-rays and gamma rays we observe from these stars. This course of is probably going distinctive for low-field magnetars, versus conventional magnetars that generate their magnetic fields in different methods.