We all know neutron star, one of the odd objects in the cosmos, now take that neutron star, it is a remnant of a massive star due to a gravitational collapse. Magnetar is also a type of neutron star, but with extremely powerful magnetic field.
How powerful this magnetic field could be? It is one thousand trillion times stronger than our planet Earth. There are only handful of magnetars are discovered in our Milky way galaxy, about 10 but recent studies shows there should be more. Because of this intense magnetic field, the surface of magnetars are heated up to 18 million degree Fahrenheit.
Magnetars are about 10 to 20 kilometers in diameter and more massive than our Sun. Unlike neutron stars, magnetars doesn't rotate rapidly - each rotation takes one to ten seconds, but the neutron stars rotates many times per second. (Fastest spinning pulsar - pulsars are also neutron star - named PSR J1748-2446ad rotates 716 times per second)
Image shows supernova remnant Puppis A - One of the brightest source of X-ray in the sky. In the zoomed in view, you can see the neutron star that is after that massive explosion of supernova, moving away from the original site of supernova at about 600 miles per second.
Life of a magnetars are relatively shorter, they loose their powerful magnetic field after some 10000 years and therefor observing them after they loose the active magnetic field will be extremely difficult.
Magnetar SGR 1900+14 is at the center of this image with surrounding gas and dust across 7 light years in infrared light - by Spitzer Space Telescope. This Magnetar is not visible in infrared but had been seen in X-ray.
It is estimated that there are more than 30 million inactive magnetars are in our own Galaxy.
It is already hard to observe neutron star or pulsar, and observing magnetar is even more harder. In 1995, NASA sent RXTE (Rossi X-ray Timing Explorer) which can observe fast moving neutron star, x-ray pulsars and other burst of x-rays.
These magnetars, the most magnetically powerful stars, are not powered by nuclear fusion - process that powers normal stars like our sun.
Now, in constellation Cassiopeia which is 18,000 light years away from our planet, a magnetar 1E 2259 is being studied. it burst in June 2002, over 80 bursts are recorded with in 4 hour period, but after that we didn't receive any burst from it.
In 2008, NASA and researches from McGill University announced that they have discovered a radio pulsar with magnetically powerful bursts, therefore scientists believe that perhaps magnetars are not rare type of neutron star but rather a phase in the life of some pulsars.
Thanks: NASA
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