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Magnetars

Information Dealing With Magnetars

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Neutron stars have been studied for decades, and emerging research is finally beginning to characterize the nature of their emission profiles. But there is still much to learn. One of the main areas of continued research is with the sub-class of neutron stars known as magnetars.

Simply, these objects are neutron stars with extremely powerful magnetic fields. While normal neutron stars themselves have incredible magnetic fields on the order of 1012 Gauss, magnetars are two to three orders of magnitude more powerful.

Creation of Magnetars

Normal neutron stars are created when a massive star runs out of hydrogen fuel to burn in its core. A cascade of events occur which eventually causes the outer envelope of the star to explode in a brilliant supernova, leaving behind the neutron core.

During this process the magnetic field of the star is increased due to a physics principle known as flux conservation. Essentially, the collapse of the star into a more compact region causes the magnetic field strength to increase in order to maintain a constant field strength far away from the star.

In the case of magnetars however, the conditions of the collapse are somewhat different. And the specific combination of spin, temperature and magnetic field strength conspire to convert some of the stars heat and rotational energy into additional field energy. This energy manifests itself as a stronger magnetic field.

While this seems to explain the observed phenomenon most commonly associated with these objects, there has been some recent data that calls into question this rather simple convolution of conditions that leads to a magnetar's creation. Data taken from the European Space Agency's (ESO) Very Large Telescope (clever name) indicate that the process may be even more complicated.

The nearest super star cluster to Earth, Westerlund 1, located roughly 16,000 light-years away, contains some of the most massive main-sequence stars in the Universe. Some of these giants have radii that would reach to Saturn's orbit, while others are as luminous as a million Suns.

Needless to say, the stars in this cluster are quite extraordinary. With all of them having masses in excess of 30 - 40 times the mass of the Sun, it also makes the cluster quite young. (More massive stars age more quickly.) But this also implies that stars that have already left the main sequence contained at least 35 solar masses. This in of itself is not a startling discovery, however the ensuing detection of a magnetar in the midst of Westerlund 1 sent tremors through the world of astronomy.

Conventionally, neutron stars (and therefore magnetars) form when a 10 - 25 solar mass star leaves the main sequence and dies in a massive supernova. However, with all the stars in Weserlund 1 having formed at nearly the same time (and considering mass is the key factor in the aging rate) the magnetar must have had an initial mass in excess of 40 solar masses.

It is not clear why this star did not collapse into a black hole. One suggestion is that perhaps magnetars form in a completely different manner from normal neutron stars. Perhaps a companion star interacted with the evolving star and caused it to expend much of its energy prematurely. The result is that much of the mass escaped through this exchange of energy, leaving too little mass behind to fully evolve into a black hole. However, there is no companion detected. Of course the companion star could have been destroyed during the energetic interactions with the magnetar's progenitor. In either case, the solution is not clear.

Magnetic Field Strength

However it forms, the defining characteristic of a magnetar is its incredibly powerful magnetic field. The strongest magnetic fields ever sustained in a scientific laboratory are on the order of 105 Gauss. This is up to 10 orders of magnitude weaker than the fields surrounding a magnetar.

Even at distances of 600 miles from a magnetar, the field strength would be so great as to literally rip human tissue apart. Placed halfway between the Earth and the Moon the magnetic field would be enough to lift metal objects such as pens or paperclips from your pockets, and completely demagnetize all of the credit cards on Earth.

These magnetic fields are so powerful that acceleration of particles easily produce X-ray and gamma-ray photons, the highest energy light in the Universe.

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