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ALL ASTRONOMICAL GRAPHICS: Picture of Magnetar

Picture of Magnetic Cataclysmic Variable: Polar or AM Herculis System

Picture of Magnetar. This image is 600 x 600 pixels; the original measures 4,096 x 4,096 pixels.

Magnetars are rapidly spinning ultra-magnetic neutron stars (they spin around their axis with a period between 3 and 12 seconds) that undergo high energy flare events which are caused by "starquakes". As their monstruous quadrillion gauss magnetic field shifts, this deformes and cracks the stellar crust making it emit flashes of soft gamma rays.

These stars, which have a diameter of only 20 kilometers and a mass of about 1.4 to 2 times the mass of our Sun, are the defunct remnants of stars which were initially up to 40 times more massive than our own Sun. It is not clear where their super-strong magnetic field comes from. This field could be of primordial origin, that is, it was already present in the interstellar cloud from which the star was born, or it could have formed later on either during the course of the evolution of the star or during the stellar core collapse to a neutron star following the supernova explosion.

Just to make a comparison... The Earth magnetic field is about 0.5 Gauss, the Sun magnetic field is about 10 Gauss while its sunspots can be up to a few thousand Gauss in strength. The strongest artificial fields ever created on Earth are of the order 10 million Gauss and only last a few microseconds. A quadrillion Gauss is 10,000,000,000,000 Gauss.

The interior is composed of a superfluid of neutrons, protons and relativistic degenerate electrons. The very deep inner core of a neutron star could be of an even more exotic nature, made up of quarks, gluons, pions and other bizarre elementary particles. The average density of a neutron star is that found in the nucleus of atoms (nuclear densities). Therefore one can imagine a neutron star to be like a single, huge atomic nucleous held together by gravitational forces, rather than by nuclear forces like it happens in an atom. The atomic mass of such an element would be of the order of A= 10^57 (a 1 followed by 57 zeros). For comparison, the atomic mass of the most common isotope of uranium is A = 238. Thus, one sugar cube of neutron star would weigh, here on Earth, a few hundred million metric tons.

See an interactive magnetar.

LINKS:

Research at the Australian National University on AM Hers etc.

VARIABLE STAR OF THE MONTH June 2001 AM Herculis: article AAAVSO the American Association of Variable Star Observers.

Research at the Australian National University on MCVs White Dwarf Stars etc.

INFORMATION ON ASTRONOMY FROM ASTROWEB



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