MAGNETARS
In 1979, scientists detected a sudden spike in gamma rays that had never before been experienced. Over the next several years, scientists detected that the same unidentified celestial body sent out powerful bursts intermittently. Scientists struggled to determine what was causing these large bursts. They theorized that whatever it was, it had to have a super-strong magnetic field in order to release the amount of energy that it did. By the time another burst was detected in 1998, scientists had come up with an explanation to explain this strange anomaly. The source of these large bursts was termed a magnetar.
A magnetar is defined as a type of neutron star that possesses the strongest magnetic field of anything in space. A refrigerator magnet measures 100 Gauss while the Earth’s magnetic field is .5 Gauss. A magnetar measures an amazing 1015 Gauss, making it at least one hundred trillion times (100,000,000,000,000) as powerful as Earth's magnetic field. Occasionally, these magnetars will experience sudden “bursts" and hurl bright flashes of gamma rays into space. Not much is known about the mechanisms that cause these magnetar “bursts,” except that they result from the instability of the star’s powerful magnetic field. One theory speculates that the unstable magnetic field causes the star's crust to fold and crack, further disrupting the star’s magnetic field and generating massive waves that release large amounts of gamma rays into space.
Although the actual theory was proposed in 1992, magnetars have not yet been categorized as a recognized major type of star. A magnetar is, however, classified as a subtype of neutron star. A neutron star is formed when a massive star dies by collapsing into a supernova or stellar explosion. The mass of a neutron star is greater than the mass of the sun, but is contained in a star with a diameter of only ten to fifteen miles, about the size of Manhattan Island in New York, This extremely dense star is composed mostly of neutrons and has a very strong magnetic field. A magnetar has a magnetic field one thousand times stronger than any other type of neutron star. This gives it an extraordinary amount of power for such a tiny star.
Normal magnetars can generate the amount of energy in one second that it takes the sun a year to produce. (1) However, the magnetar bursts in 1979 and 1998 were abnormal even for magnetars because they were approximately one thousand times brighter than a normal magnetar. In fact, during the brief period of these outbursts, the magnetars-were brighter than supernovas. (2) The energy that radiates from supernovas in the short period between when they explode and when they fade is equal to the amount of energy the sun will radiate over ten billion years. (3) Yet the two abnormally strong magnetars of 1979 and 1998 surpassed supernovas in both brightness and energy. (4) Magnetars are also unique because they produce multiple bursts of light that last only a second, much like a pulsar. A pulsar is a periodic flash of light from a star that is sending a constant beam of energy or light away from itself. Due to the pulsar’s rotation, it appears to be blinking on and off as its light sweeps over Earth.
Scientists predict that there are likely millions of magnetars in the galaxy, but only five magnetars have been discovered since the first one was observed in 1979. A recent magnetar was observed in late December 2004. This burst is considered the brightest burst ever. It was only .25 seconds long, but it was powerful enough to overwhelm energy detectors on the many satellites in space so that no energy measurement could be taken. It also interfered with radio communication on Earth. The magnetar was an estimated thirty to fifty thousand light years from Earth. Scientists say that the magnetic force is so strong on a magnetar that it could wipe a credit card clean, or make it ineffective, from a distance of one hundred thousand miles, or about half the distance to the moon.
Although scientists have only been able to detect a few young magnetars, they expect to detect many more in the future. Much about magnetars remains a mystery, and they are a challenge for scientists to study since they appear once every few years and are observable only for a second. Scientists hope to determine more about what causes the instability within a magnetar’s magnetic field so that they can better understand these powerful bursts.
* gamma ray: a type of radiation with a short wavelength that can pass through solid objects
* celestial: in or relating to the sky; heaven, or space
* crust: the thick outer surface of a planet