Why do pulsars have a magnetic field

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Why are neutron stars called stars? Good questions! Neutron stars are magnetic because their interiors contain powerful electrical currents. In that sense, they have more in common with electromagnets, which are associated with electric fields, than with toy magnets, which are permanent magnets and require no electric field to incite their magnetic properties.

The Zeeman effect is a splitting of atomic lines due to magnetic fields. Neutron stars, however, have such huge magnetic fields that the structures of the atoms on the surface are altered. Rather than being basically spheres, the atoms become narrow and short cylinders aligned along the magnetic field. Snapshot : ALMA spots moon-forming disk around distant exoplanet. A handful of neutron stars have been found sitting at the centers of supernova remnants quietly emitting X-rays.

More often, though, neutron stars are found spinning wildly with extreme magnetic fields as pulsars or magnetars. In binary systems, some neutron stars can be found accreting materials from their companions, emitting electromagnetic radiation powered by the gravitational energy of the accreting material. Below we introduce two general classes of non-quiet neutron star — pulsars and magnetars. Most neutron stars are observed as pulsars.

Pulsars are rotating neutron stars observed to have pulses of radiation at very regular intervals that typically range from milliseconds to seconds. Pulsars have very strong magnetic fields which funnel jets of particles out along the two magnetic poles. These accelerated particles produce very powerful beams of light.

Often, the magnetic field is not aligned with the spin axis, so those beams of particles and light are swept around as the star rotates. The strange state of matter inside neutron stars is what scientists call " nuclear pasta ": Sometimes, the atoms arrange themselves in flat sheets, like lasagna, or spirals like fusilli, or small nuggets like gnocchi.

Some pulsars also prove extremely useful because of the precision of their pulses. There are many known pulsars that blink with such precise regularity; they are considered the most accurate natural clocks in the universe.

As a result, scientists can watch for changes in a pulsar's blinking that could indicate something happening in the space nearby. It was with this method that scientists began to identify the presence of alien planets orbiting these dense objects.

In fact, the first planet outside Earth's solar system ever found was orbiting a pulsar. Because pulsars are moving through space while also blinking a regular number of times per second, scientists can use many pulsars to calculate cosmic distances. The changing position of the pulsar means the light it emits takes more or less time to reach Earth. Thanks to the exquisite timing of the pulses, scientists have made some of the most accurate distance measurements of cosmic objects.

Pulsars have been used to test aspects of Albert Einstein's theory of general relativity, such as the universal force of gravity. The regular timing of pulsars also may be disrupted by gravitational waves — the ripples in space-time predicted by Einstein and directly detected for the first time in February There are multiple experiments currently searching for gravitational waves via this pulsar method.

Using pulsars for these types of applications depends on how settled they are in their rotation thus providing very regular blinks , Ransom said. All pulsars are slowing down gradually as they spin; but those used for precision measurements are slowing down at an incredibly slow rate, so scientists can still use them as stable time-keeping devices.

All pulsars slow down gradually as they age. The radiation emitted by a pulsar is jointly powered by its magnetic field and its spin.

As a result, a pulsar that slows down also loses power, and gradually stops emitting radiation or at least, it stops emitting enough radiation for telescopes to detect , Harding said. Observations thus far suggest that pulsars drop below the detection threshold with gamma-rays before radio waves.

When pulsars reach this stage of life, they enter what's known as the pulsar graveyard. Pulsars that have stopped emitting may be considered ordinary neutron stars by astronomers. When a pulsar forms from the wreckage of a supernova, it spins fast and radiates a lot of energy, Ransom said. The well-studied Crab Pulsar is an example of such a young pulsar.

This phase may last for a few hundred thousand years, after which the pulsar begins to slow down and only emit radio waves. These "middle-age" pulsars likely make up most of the population of pulsars identified as emitting only radio waves, he added. These pulsars live for tens of millions of years before eventually slowing down so much that they "die" and enter the pulsar graveyard.

But if the pulsar sits near a stellar companion, it may be "recycled," meaning it siphons material and energy from its neighbor, increasing its spin to hundreds of times per second — thus creating a millisecond pulsar, and giving the once-dead pulsar new life.

This change can occur anytime in a pulsar's life, meaning a "dying" pulsar's rotation rate can increase over hundreds to millions of years. The pulsar begins to emit X-rays, and the pair of objects is known as a "low-mass X-ray binary," Ransom said.