The Snake at the Centre of the Galaxy
There's a kinky Snake lurking near the middle of our Galaxy. It's a monster 150 light years long and two to three light years wide. And according to Dr Gregory Benford of the University of California, Irvine, who has been working on the nature of the beast, it has an electrifying character - it's physically like a lightning discharge frozen in space.
Dr Benford develops his theories about the Snake writing in the 1 March issue of the Monthly Notices of the Royal Astronomical Society. He has argued that electrical current discharges on such a large scale could last for millions of years in the environment prevailing in the Galaxy's central regions. But the fact that the Snake is wiggling, he says, shows that it is mortal and will eventually die.
The Snake lies in the constellation Sagittarius where it was discovered in 1992 by radio astronomers. Twenty-two similar filament-like structures are known near the galactic centre, but the Snake is the oddest and largest. It is uniquely kinked in two places and its kinked parts emit its strongest radio waves.
Dr Benford suggests that the electric currents that make the Snake and other filaments are generated by electrically conducting molecular clouds travelling through the magnetic field pervading the Galaxy. The clouds are effectively the 'battery'. This idea is supported by the observation that molecular clouds moving contrary to the general rotation of the Galaxy have been found associated with the filaments.
Filaments like the Snake form near the Galaxy's centre because the general magnetic field of the Galaxy is strongest there, decreasing with distance from the centre. The Snake is located farther from the galactic centre than the other known filaments, so it is in a region of somewhat lower magnetic field. That is why the Snake is wiggling, says Dr Benford. The field isn't strong enough to restrain it more firmly.
Building up a picture of the Snake's behaviour, Dr Benford can also explain why the kinky bits are the brightest radio emitters. Electrically charged particles are accelerated by shocks in these regions. These particles emit synchrotron radiation as they spiral through the magnetic field.
'By looking towards the galactic centre' Dr Benford comments 'we can learn how nature makes long-lived structures of this sort - which we've so far failed to do in the laboratory in nuclear fusion research programs. Understanding an astronomical object like the Snake could have down-to-Earth applications, maybe even helping solve the problem of a long-term supply of energy'.
Issued by: Dr Jacqueline Mitton
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