One of the latest phenomena in this category is the “fast radio burst” or FRB, which is a pulse of radio waves that is extremely brief – a matter of fractions of a second. The first detection of an FRB was made in 2007, from examination of signals received in 2001 by the Parkes radio telescope in Australia. The pulse lasted for only 4.6 milliseconds (a millisecond is a thousandth of a second).
Despite much analysis of data received by radio telescopes across the world, only a handful of FRBs have been found to date, and only one (in 2014) has been observed as it happened.
Astronomers would love to be able to track an FRB to its source, and this can best be done by getting a number of radio telescopes in different countries to get a fix on a signal, once one has been detected. In April 2015 they were able to do this after an FRB was picked up that lasted for less than a millisecond. What they also discovered was that the burst produced a “radio afterglow” that continued for six days. This gave the astronomers at Parkes enough time to alert the Subaru telescope in Hawaii to focus on the source, which in turn led to the discovery that the signal came from an elliptical galaxy some 7 billion light years away. The radio burst therefore started its journey several billion years before Planet Earth existed!
Various theories have been proposed to explain the cause of a fast radio burst, and – as might be expected – alien intelligence of some kind is on the list. However, the theory that is currently being given most weight is that FRBs originate from the collision of two neutron stars (a neutron star is the extremely small and dense residue of a collapsed giant star). Such an event would produce a massive amount of energy that would also include gravitational waves, such as are believed to result from the merging of black holes. It is hoped that a gravitational wave source will be confirmed as coinciding with that of a fast radio burst, but this has yet to happen.
However, not all cosmologists accept the idea that FRBs are caused by colliding neutron stars, or that there need be only one explanation. Another candidate is a flare from a magnetar, which is a neutron star with a powerful magnetic field, the decay of which can produce x-rays and gamma rays.
Speculation will doubtless continue until more observations can produce a more definitive answer to this particular problem.
© John Welford
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