Journal Club: The Pulsar That Wasn’t

Article written: 24 Dec , 2011
Updated: 24 Dec , 2015


According to Wikipedia, a Journal Club is a group of individuals who meet regularly to critically evaluate recent articles in the scientific literature. Since this is Universe Today if we occasionally stray into critically evaluating each other’s critical evaluations, that’s OK too.

And of course, the first rule of Journal Club is… don’t talk about Journal Club. So, without further ado – today’s journal article involves the mysterious case of PSR J1841-500, the pulsar that didn’t pulse.

Pulsars are neutron stars – with polar jets. They rotate quite fast and when one of those polar jets line up with Earth we detect a pulse of radio light. This is a very regular and very predictable pulse – although when measured over long time periods, the pulses slowly decline in frequency as magnetic forces create drag that slows the neutron star’s spin.

But PSR J1841-500 is an oddball – when first discovered, it pulsed every 0.9 seconds. Then for reasons unknown, it stopped pulsing for a period of over 500 days – after which it just picked up where it left off. There are at least two other pulsars known to have demonstrated such ‘switch on – switch off’ behaviour, although neither had anything like the switch-off duration of PSR J1841-500.

It is known that now and again neutron stars experience a ‘glitch’, a kind of a starquake, as the intense gravity of the star crunches its internal structure down to an even more compact state. This can change its spin and hence its pulse rate.

However, it’s not clear if glitch phenomena would help explain the extended ‘switch-off’ phenomenon observed in PSR J1841-500. Looking for other anomalies, the authors point to the unusual proximity of the magnetar IE 1841-045, which might be having some (unknown) effect on its neighbor.

The authors then conclude with the interesting suggestion that if this behavior is common, then we may be missing lots of pulsars that were in a ‘switched-off’ state when their particular region of the sky was last surveyed. This means we actually need to undertake repeated surveys – which should hopefully keep more astronomers in a job.

So – comments? Are the authors just building an overblown story out of a measurement error? Is there some weird magnetic dance going on between two proximal neutron stars? Want to suggest an article for the next edition of Journal Club?

Otherwise, happy holidays and all that stuff. SN.

Today’s article:
Camilo et al PSR J1841-0500: a radio pulsar that mostly is not there.

28 Responses

  1. pj1500 says

    Black Hole eclipses?

  2. Anonymous says

    I would thing the sudden change in structure could have changed swede the axes enough that the pulse was aimed away from us, giving the illusion of switching off, but after stabilizing it realigned to the forces that be, thus switching back on.

  3. Anonymous says

    The “polar jets” are not aligned with the rotational axis, but the magnetic axis, which is at an angle the the rotational axis. Otherwise it wouldn’t pulse. The beam sweeps round like a lighthouse, and we happen to see those whose beams shines on us once a circuit.. The relationship of the magnetic axis of a neutron star to it’s rotational axis is a another kettle of fish, but I could entertain the idea that it varies under the influence of starquakes or interactions with other local massive bodies. We happened to be off-beam for 500 days till it settled back.

    • “…Otherwise it wouldn’t pulse…” Of course! Or OK I suppose it’s bleeding obvious, but I had never stopped to think why there was a pulse. Brilliant.

      Another vote for the star-quake-sent-it-off-kilter theory.

  4. ngwc7 says

    Don’t we see pulsars when the polar jets line up with Earth? What if they rotate (i doubt i’m using the right terminology) and they move away from our line of sight?

    Pardon my ignorance..

    • You mean – what if the rotational axis shifts such that the pulse of a magnetic bipolar jet moves away from our line of sight?

      Yes that seems to be the prevailing view here.

      Still, it’s funny how most other pulsars don’t seem to demonstrate such shifting behaviour.

      Or maybe we just haven’t been watching them all long enough – and this behaviour may be more prevalent than we realise?

      • Ernie says

        It seems like an easy theory to test. Set up a hundred small (well, large enough to detect these pulsars, although I recall these signals are pretty strong) radio antennae to continuously track as many pulsars for as long as you want. It may even be possible to get amateurs to help crowdsource the project. Come back with the results in a few years. I suspect this happens more than we think it does.

  5. Tim Jonson says

    Very nice tips. I like it. Thank you. free government cell phones

  6. Anonymous says

    The Solar system orbits the center of the Milky Way at about half a billion miles per hour.

    Is it just possible that the Earth has just moved out of the narrow beam of pulse???

  7. Anonymous says

    “The authors then conclude with the interesting suggestion that if this behavior is common, then we may be missing lots of pulsars that were in a ‘switched-off’ state when their particular region of the sky was last surveyed. This means we actually need to undertake repeated surveys – which should hopefully keep more astronomers in a job.”

    What would be the negative affect of not knowing about them?

    • HeadAroundU says

      That’s a pretty obvious question. Generally, not knowing is a problem. Better statistics, better theories. It could improve our understanding of how our galaxy works..etc

    • A tree would fall in a forest without making a sound – unless a group of unemployed astronomers were out there on a work for the dole program.

  8. Kevin Parker says

    Obviously, it’s another scam like global warming designed to keep scientists in business. 😉

  9. Anonymous says

    The idea that pulsar are thin precessing blazing jets are considered in my early and late attepts to solve since 1998 the GRB puzzle: during SN and pulsar jets inside maybe beaming generally off axis with the observer..(since 1998 we did see SN and GRB april 25)
    Therefore most SN appear spherical and symmetric
    However when looking in large Universe (large redshift) the thin jet may blaze
    as a GRB…its decay in power and time by power law reduce the SN-pulsar jet as a SGR
    or as a Gamma pulsar (or X-radio, depending on the angle of view)
    In our galaxy the GRB-SGR connection has been claimed by me since a long time.
    The precessing jet may picture a twin cone in the space. Its tangency
    to us explain the beaming and the blazing..Inner spinning jet explain the GRBor SGR flux trembling. The disturbance by accreting disk or companion on the precessing cone geometry may deflect the cone and shut down the beeming or jut reopen the PSR activity as the SGR activity…
    See for instance

    Title: GRBs by thin persistent precessing lepton Jets: the long life GRB110328 and the Neutrino signal; : Daniele Fargion and references

    . arXiv:0910.2273
    Title: An apparent GRBs evolution around us or a sampling of thin GRB beaming jets?
    : Daniele Fargion.; Journal-ref: Mem. S.A.It. Vol. 81, 440 c SAIt 2010

    arXiv:astro-ph/0501403 [pdf, ps, other]
    Title: GRBs-SN and SGR-X-Pulsar as blazing Jets
    D. Fargion
    Journal-ref: Chin.J.Astron.Astrophys. 3 (2003) 472-482

    Title: GRBs and SGRs as precessing gamma jets
    : Daniele Fargion; Journal-ref: Astron.Astrophys.Suppl.Ser. 138 (1999) 507

    There are published by us many more articles claiming the blazing nature of GRB and SGRs..
    connected to such long scale rebrightening of a SGR or pulsar…No magnetar explosions nor fireball multishell variability..Just thin (micro-nano sr) precessing jets.

    Thank you for the attention
    Daniele Fargion

    • Torbjörn Larsson says

      Not to offend, but I feel I need to point out that this may stray close to this science blog policy of not publishing comments with personal theories. None of these, and presumably then “many more articles”, seems to be peer reviewed!?


      But I remember the infamous Journal of Cosmology publications. [Still alive web site in the face of a promise to close down the journal during early 2011. Now used to get promotional redirects to Amazon, so don’t go there!] Tied to that I seem to remember mentioned a chinese astrophysics journal that was also used by crackpots to get their papers published against some fee.

      I don’t have access to Scopus, nor the necessary familiarity to look for journal rankings. But I found the SCImago search engine based on Scopus. And that journal isn’t even ranked there.

      What is ranked is a “Chinese Astronomy and Astrophysics” which is an Elsevier printing. “Translations of papers from two new journals the Chinese Journal of Space Science and Acta Astrophysica Sinica are added to the translation of Acta Astronomica Sinica to form the new journal Chinese Astronomy and Astrophysics.” (It starts out with a Q2 ranking but slips to a Q3 today.)

      Presumably the SCIMago lists peer reviewed publications. The Chinese A&A is a reprint where “All [the above] journals employ a peer referee system.”

      Indeed, the IOP description of Chin.J.Astron.Astrophys. describes it as an edited press-to-publish journal with some review articles. I.e. no peer review.

      Similarly, the Astron.Astrophys.Suppl. is not listed in SCImago. “Astronomy and Astrophysics, Supplement Series (A&AS) published both on paper and electronically data papers, either observational or theoretical, as well as extensive data material forming the basis of papers with astrophysical results published in the Main Journal. Papers on instruments, observational techniques, data processing and computational methods were also published in A&AS.”

      I.e. again no peer review, the actual results were published in the A&A. These journals are today combined, perhaps to close the gap that allowed for non-technical matters to slip through.

  10. HeadAroundU says

    It’s all because of Steve supernova Nerlich SN. :d

    I wonder, is it both jets shinning at us? Rotating. Or only northern or southern jet?

    • Anonymous says

      That depends. Mostly it’s just one jet pointing at us. But on special circumstances it can happen that both jets can be seen from earth.

  11. Anonymous says

    How bout a magnetic polarity reversal every 500 days?

  12. Anonymous says

    The magnetic field does not likely shift its orientation. These magnetic fields are 10^{12}Gauss and the energy density of this field is B^2/4?? ~ 10^{17}j/m^3. If the field changes its orientation in the material it requires an enormous change in the magnetization and some energy source to do that. The EM fields are produced by material or charged particles interacting with the magnetic field. I think it is more likely that the source of this material, such as an accretion disk, shuts off.

    The pulsar data at the point it shuts off might contain information concerning the physics of this phenomenon.


  13. A. Houser says

    Come on guys, clearly intelligent extraterrestrials blocked the pulses. This way they don’t have to worry about generating enough energy to broadcast their signal pretty far into space–it’s already being done! All they have to do is prevent is from that radiation being shot into the rest of the galaxy. Did sailors on ships during the World Wars turn their signal lamps on and off? Of course not! They used shutters instead.

    I’m surprised that nobody has realized this by now. 😉

  14. Wezley Jackson says

    OK.. I’ll throw my hat in the ring 😉 ..

    Last night standing on the coast of an Australian beach watching a lighthouse beam sweep across a roaring midnight ocean got me thinking of these universal beacons…

    Intuitively my first thoughts and instincts were the same as lcrowell’s – That an extremely dense, compact object such as a neutron star should not easily change its magnetic poles… and this would seem reinforced by this article and the theories of the scientists quoted:
    Title: Are Pulsars Giant Permanent Magnets?

    However, after researching starquakes (which had very little knowledge of), it does seem to me to be a leading contender for the switch-off / switch-on intermittent behaviour seen (as described eloqently by bk_2 in his/her post below…

    According to this article:
    Title: Scientists Can Predict Pulsar Starquakes
    “By monitoring the pulsar spin rate and changes in the spin, we can pin down a starquake event to within a couple of days,” Middleditch said. “These and other details have helped to simplify what has, until now, appeared to be a bewildering assemblage of facts about starquakes in pulsars. … The pulsar is known for its frequent quakes, which scientists call glitches. Pulsars are born spinning rapidly, but gradually slow down. PSR J0537-6910 spins at a rate of about 62 times per second, or 62 hertz. During a glitch, this pulsar’s spin jumps up as much as one cycle every seven hours, a greater gain than what is seen in any other pulsar. Then the pulsar proceeds to slow down again.
    After about 10 glitches since monitoring began in 1999, the scientists saw a pattern. The amount of increase in spin with each glitch could be translated directly into the number of days until the next glitch. Larger glitches meant a longer wait until the next one.
    The predictive nature of these glitches firms up the leading theory on their cause. Pulsars have a solid crust, but are permeated with a liquid neutron superfluid.
    Much of the crust’s own superfluid does not slow with the pulsar, but when the difference in rotation rates exceeds a certain threshold, a large fraction of the excess can be dumped into the solid crust through massive cracking, making the pulsar spin faster.
    // end excerpt //

    After reading this I wanted to dig deeper to see if the 500 days mentioned in this article for PSR J1841-500 was highly anomalous … My reasoning being if it was highly odd, then the permanent magnet theory (and by extension accretion switch on/off) would start to wrestle back my agreement forming with the glitches and starquakes cause intermittent behaviour crowd.. Also in the back of my mind was whether the authors suggestion of a the neighboring magnetar might also play into things…

    Here is what I found – quoting article:
    Title: Astrophile: Stopped clocks deepen pulsar enigmas
    With an “off” period of 580 days, Camilo’s pulsar has taken by far the longest break seen so far. Having switched back on only in August this year, it is too early to tell whether the year on/year-and-a-half off cycle is a regular thing, but Camilo says it makes him wonder what other pulsars are hiding.
    // end excerpt //

    So it would seem to me that the starquake theory based on observation of glitches has the deepest explanation so far. Yes the scientists who propose the starquake explanation do so with some very informed assumptions and educated guesses.
    After reading deeper I have actually changed my mind and now accept starquakes as the leading theory and it would seem magnetic poles of pulsars may either shift (which is incredible and amazing considering the huge strength of the fields as pointed out by lcrowell if this is the case) or perhaps the fields are switching off due to the eruptions of neutron superfluids onto the neutrons stars surface.
    Only further observations and testing of these hypotheses will tell and I am fascinated by these dense objects and their lighthouse-like behaviour…

    Happy Holidays,

    ps. Enjoying the popular references in these articles Steve – we are all beautiful individual snowflakes 😉

    • Anonymous says

      If the magnetic field in a pulsar were generated by a dynamo effect, rather than being a permanent magnet, I think that would require some new physics. I am not sure how one gets that in a dense liquid of neutrons. It is my understanding that pulsars or magnetars do adjust their magnetic field rather violently, releasing the crust of degenerate iron at relativistic velocities which then crashes back to the surface under the force of gravity. A whole collapse of the magnetic field, which largely provides a pressure against gravitational collapse, would mean an enormous amount of energy is converted to another form, and if the magnetic field turns back one there must be a supply of energy, a lot of it as well, which feeds the dynamo.


  15. magnus.nyborg says

    Precession would still be a cyclical phenomenon, so if precession are responsible for the turn-off, the turn-off should also repeat over longer periods of time.

    A collapse/dispersion of the accretion disc does seem more plausible, maybe even with a (small) dislocation of the magnetic fields.

  16. Tyler Uematsu says

    I hope this isn’t too much of a stupid question, but could something large have passed in front of the pulsar, only giving the appearance that it did indeed “shut down”? If I remember correctly, neutron stars aren’t all that big; by my thinking it wouldn’t take something too large to entirely block it out from our field of vision…

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