What is Magnetar?
A magnetar is a type of neutron star with an extremely powerful magnetic field, the decay of which powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays. The theory regarding these objects was proposed by Robert Duncan and Christopher Thompson in 1992, but the first recorded burst of gamma rays thought to have been from a magnetar was detected on March 5, 1979. During the following decade, the magnetar hypothesis has become widely accepted as a likely explanation for soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs).
Like other neutron stars, magnetars are around 20 kilometres (12 mi) in diameter and have a greater mass than the Sun. The density of the interior of a magnetar is such that a thimble full of its substance would have a mass of over 100 million tons. Magnetars are differentiated from other neutron stars by having even stronger magnetic fields, and rotating comparatively slowly, with most magnetars completing a rotation once every one to ten seconds, compared to less than one second for a typical neutron star. This magnetic field gives rise to very strong and characteristic bursts of X-rays and gamma rays. The active life of a magnetar is short. Their strong magnetic fields decay after about 10,000 years, after which activity and strong X-ray emission cease. Given the number of magnetars observable today, one estimate puts the number of inactive magnetars in the Milky Way at 30 million or more.
Starquakes triggered on the surface of the magnetar disturb the magnetic field which encompasses it, often leading to extremely powerful gamma ray flare emissions which have been recorded on Earth in 1979, 1998, and 2004.
Magnetars, the Most Magnetic Stars In the Universe
“We only know of about 10 magnetars in the Milky Way galaxy.” remarked Dr. Peter Woods of the Universities Space Research Association. “If the antics of the magnetar we are studying now are typical, then there very well could be hundreds more out there.” NASA research has suggested there may be far more magnetars than previously thought.
Observing the explosions from these celestial bodies has been tricky. The answer lies in the timing. So how do the researchers observe what has never been seen? Leave it to NASA to develop the perfect piece of equipment to handle the job.
The Rossi X-ray Timing Explorer (RXTE), launched in December 1995 from Kennedy Space Center, Fla., was designed to observe fast-moving neutron stars, X-ray pulsars and bursts of X-rays that brighten the sky and disappear.
Some pulsars spin over a thousand times a second. A neutron star generates a gravitational pull so powerful that a marshmallow impacting the star’s surface would hit with the force of a thousand hydrogen bombs.
Magnetars, the most magnetic stars known, aren’t powered by a conventional mechanism such as nuclear fusion or rotation, according to Dr. Vicky Kaspi. “Magnetars represent a new way for a star to shine, which makes this a fascinating field,” said Kaspi.
Although not totally understood yet, magnetars have magnetic fields a thousand times stronger than ordinary neutron stars that measure a million billion Gauss, or about a hundred-trillion refrigerator magnets. For comparison, the Sun’s magnetic field is only about 5 Gauss.
Image 1 | Artist’s conception of a magnetar, with magnetic field lines
Image 2 | Magnetar SGR 1900+14 is in the exact center of the image, which shows a surrounding ring of gas seven light-years across in infrared light, as seen by the Spitzer Space Telescope. The magnetar itself is not visible at this wavelength, but it has been seen in X-ray light.
Image 3 | On 27 December 2004, a burst of gamma rays arrived into the Solar System from SGR 1806-20 (artist’s conception shown). The burst was so powerful that it had effects on Earth’s atmosphere, at a range of about 50,000 light years.