London, July 17 : A study of light from distant quasars is casting serious doubt on the theory that galaxies "spin" their own fields over many billions of years.
According to a report in New Scientist, the study suggests that young galaxies could not have spun enough times to have built up such large magnetic fields.
Large galaxies such as the Milky Way have magnetic fields that span their entire length and breadth.
Astrophysicists believe a mechanism similar to a dynamo builds up these fields from small "seed" fields spewed out by supernovae and black holes. As the galaxy rotates, charged particles move across these seed fields and augment them, gradually creating a stronger field.
To test the theory, Martin Bernet and Francesco Miniati of the Swiss Federal Institute of Technology in Zurich and colleagues looked at light from 71 quasars - very bright, distant galaxies - that were anywhere from 5.5 billion to 10.5 light years away.
Any galactic magnetic fields that the light passes through en route to Earth, including those of the quasars themselves and of our own galaxy, cause the angle of polarisation of the light to rotate.
The cumulative rotation - called the Faraday rotation measure (FRM) - is an indication of the total strength of these fields.
If the dynamo theory is correct, after a quasar's light has passed through the halo of a distant galaxy, along an otherwise unimpeded path towards Earth, its FRM should be low.
That's because the quasar light passed through that galaxy when it was young, before it had been able to spin enough times to have built up large fields.
"What we found, somewhat surprisingly, is that magnetic fields, as far as we can look back, are as strong as they are today," said Miniati.
This is a problem, because the dynamo mechanism would have to have worked far more rapidly than is thought possible.
According to Miniati, one explanation is that some as-yet-undiscovered processes are producing much stronger seed fields than expected. Another intriguing possibility is that the strong seed fields are primordial, produced in the first instants after the big bang.
The real evidence for such primordial fields will come from the cosmic microwave background, the radiation left over from the big bang. (ANI)
© 2007 ANI