And something else is a mystery. Some pulsars are extremely moody: their radio radiation suddenly drops extremely within seconds and changes their frequency. The timing of the jump is not predictable. After a few hours or days, the pulsars then return to their original state, as if nothing had happened. "What causes these stars to change their condition, we do not know - we are completely in the dark, " says astronomer Joanna Rankin of the University of Vermont.
Global toggle switch
Hermsen, Rankin and her team have now examined one of these chameleon pulsars in more detail - not only its radio-wave emissions, but in parallel also the X-rays it emits with the help of the X-ray satellite XMM-Newton of the European Space Agency ESA. They discovered something surprising: Whenever the radio radiation of the star suddenly decreased, its emissions in the X-ray range increased drastically - similar to when a toggle between the different wavelength ranges of radiation is switched. "To our great surprise, we found that as the signal brightness decreased by half, the X-ray brightness was doubled, " says Hermsen. And only in its bright phase does the X-ray pulsar pulsate measurably. display
This observation, however, torpedoes previous assumptions about the origin of the fluctuations, which were thought to be due to a local influence of the radio radiation by the magnetic field at the poles of the star. However, the now discovered change between the short-wave X-ray and the long-wave radio radiation can not be explained by such local processes. "Something has to happen globally, " says Rankin. The entire global environment of the pulsar must undergo a transformation in order to be able to switch so strongly in just over one second. According to current theory, the radio waves arise when high-energy particles are thrown outwards into the magnetic field, but the X-rays are formed when these particles are accelerated inwards and strike the surface of the pulsar.
What exactly animates the chameleon pulsars to their changeable behavior, is therefore not clear even after the new observations. The astronomers now know, after all, that the process probably covers the entire magnetic field of the neutron star. How exactly, should now further investigations on other, also between radio and X-radiation changing pulsars clarify.Wim Hermsen (University of Amsterdam) et al .: Science, doi: 10.1126 / science.1230960