Unsteady Cosmic Lighthouses
Pulsars are considered prime examples of natural punctuality. Every few milliseconds, as they spin, they point towards Earth and send us a short pulse of radio waves. Not so the newly discovered neutron stars - apparently they are often not in the mood and take long breaks. The first pulsars were believed to be contact signals from small men from space. Radio waves always hit the earth from the same direction with unprecedented precision – up to several hundred times per second. But science fiction fans were soon disappointed when it was revealed that the regular characters had a natural origin. However, not a banal one. The transmitters are fast rotating neutron stars that are formed when a very massive star explodes at the end of its life and its center collapses. The remaining matter reaches such an enormous density that the atoms are squeezed together to form neutrons. A neutron star no longer emits light in the visible range, but it rotates extremely fast and emits radio waves, which it bundles with a strong magnetic field and regularly sends around like the beam of a lighthouse. Because these appear as isolated pulses seen from Earth, these neutron stars have been dubbed pulsars.
As if that wasn't exotic enough, astronomers led by Maura McLaughlin from the Jodrell Bank Observatory have now identified almost a dozen neutron stars that don't seem to think too highly of the reliability of their conspecifics. Now and then a radio signal lasting two to thirty milliseconds and then a long break that can last up to three hours – that's how rare the new objects are. Such unreliable behavior doesn't earn the title "pulsar," so the researchers refer to these casual radio operators as rotating radio transients, or RRATs for short.
The first signs of the RRATs were found in data from 1998 to 2002. At that time, a targeted search was made for the sources of individual radio signals. The astronomers identified 11 candidates, and all 11 were observed sparking several times later. However, the unreliability of the objects does not allow for impressive statistics: the shyest specimen showed up just four more times and the most extroverted representative only 229 times.
Nevertheless, the researchers were able to deduce some hidden regularities in several cases. In ten of the eleven sources, periods of between 0.4 and 7 seconds are hidden behind the flashes, although a signal is not actually detected every round. This points to rotating neutron stars as the origin, so to speak cosmic lighthouses that have to struggle with disruptive power failures for their lamps for long periods of time. However, the cause of these star-level failures remains a great mystery.
A mystery to be solved as RRATs are probably not uncommon in the sky. They tend to be concentrated near the galactic plane, i.e. in the area of the disk of our Milky Way. The scientists say there are roughly 100,000 of them in the galaxy. That would make them far more common than the punctual pulsars. Somehow human - because even here on earth the number of loafers is said to significantly exceed the number of pedants. Perhaps something earthly is reflected in the firmament.
