WHAT ARE PULSARS?
As we’ve discussed previously, pulsars are the intimately related to neutron stars — the dense remnants of massive stars that have gone supernova. During their demise, a large fraction of the remaining mass of the now-defunct star is packed tightly into an object only a few kilometers across.
In addition to their massive density, these objects also have magnetic fields that are extremely powerful (typically about one trillion times stronger than Earth’s). They are so strong, in fact, that as they spin, they unleash a stream of high-energy particles from their poles. If the poles are pointed toward Earth, directly in our line of sight, they appear to pulsate, hence the term ‘pulsars.’
A STAR WITH MULTIPLE PERSONALITIES:
The star we’re going to talk about today, dubbed PSR B0943+10, lies some 3,000 light-years from Earth in the Leo constellation. Instead of calling it by its formal name, we’re just going to refer to it as ‘the bipolar pulsar’ for the sake of this article. Capisce? Capisce.
Anyway, our star has been spotted spontaneously shifting between x-ray emissions and radio waves. This isn’t so unusual in and of itself, as radio frequencies are known to shift when alter-egos start to manifest, but this is the first documented case of a pulsar exhibiting changes in variability with x-ray emissions as well (in fact, it’s unusual for pulsars to display any x-ray activity at all).
OBSERVATIONS OF THE BIPOLAR PULSAR:
The team, who hail from two different places – the Netherlands Institute for Space Research and the University of Amsterdam – have revealed that that the pulsar, which is about 5 million years old, has an orbital period of merely 1.1 seconds, making it quite a bit slower than most pulsars of the same caliber. However, the intensity of the radio pulsations recorded by astronomers show that this can literally change in an instant. All the while, the bipolar pulsar continues to to generate a faint x-ray signal along its magnetic lines. This signal is created when charged particles radiate along the magnetic lines then they, in turn, bombard the pulsar’s magnetic poles.
After the initial discovery, the team became inclined to know how much the x-ray emissions varied between the two different modes (the ”radio-bright’ mode and the quiet mode). So, like in most astronomical endeavors, a telescope was pointed directly to the area to gather enough data to accurately compare the two extremes. It was then that the multiple personalities were revealed.
As depicted in the two illustrations above, the bipolar pulsar is seen during its ‘on-mode.’ (top right) During this window of activity, the cones are lit up. Now, when we refer to the image on the top left, we see the pulsar at shorter wavelengths conductive to showing x-ray emission, revealing that when the pulsar is most active at spewing radio waves, it is mum on the x-ray front.
The bottom graph depicts the pulsar’s x-ray and radio emission when in off mode. Conversely to its on-mode, during its off-mode – when the pulsar develops ‘hot-spots’ located near its magnetic poles – it’s very energetic at x-ray wavelengths, but is mum on the radio front. Strangely, as stated by the team, at this time, the pulsar “exhibits variations in its X-ray emission that mimic in reverse the changes seen in radio waves.” [Reference]
UNWRAPPING THE ENIGMA:
According to Win Hermsen, the study’s lead author, nothing at this particular moment can account for the inconsistencies seen in the x-ray and radio emissions of the bipolar pulsar. This has left Hermsen and his team scratching their heads in unison. This discovery will likely spawn the creation of new models to help deduce exactly what is going on.
In the meantime, team members believe the pulsar is undergoing rapid changes in its magnetosphere (an illustration of which can be seen to the right), causing it to switch between radio and x-ray emissions. (Another paper published in the journal ‘arxiv.org’ suggests that the pulsar could actually be a low-mass quark star) However, the ”how” is more important than the “why” right now. Perhaps after more examples of pulsars are found and compared, we will have a better understanding of the mechanisms that power pulsars and their counterparts, millisecond pulsars.
PSR B1822-09 will be observed with several other telescopes grounded in India, the United Kingdom, and the Netherlands, along with the XMM-Newton Space Observatory.