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Space Science

New Class of Pulsars Discovered 93

Posted by Soulskill from the for-all-your-gamma-ray-needs dept.
xyz writes "NASA's Fermi Gamma-ray Space Telescope has discovered a new class of pulsars which emit purely in gamma rays. A pulsar is a rapidly spinning neutron star, and of the nearly 1,800 cataloged so far, only a small fraction emit at frequencies higher than radio waves. The gamma-ray-only pulsar, which lies within a supernova remnant known as CTA 1, is silent across parts of the electromagnetic spectrum where pulsars are normally found, indicating a new class of pulsars. It is located 'about 4,600 light-years away in the constellation Cepheus. Its lighthouse-like beam sweeps Earth's way every 316.86 milliseconds. The pulsar, which formed in a supernova explosion about 10,000 years ago, emits 1,000 times the energy of our sun.'"
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New Class of Pulsars Discovered More

New Class of Pulsars Discovered

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  • First Pulsar Post (Score:3, Funny)

    by Fishead ( 658061 ) on Sunday November 02, 2008 @11:17AM (#25603009)

    Odd thing is that the signal seems to be carrying a message. We have decoded it, and it seems to read: F-I-R-S-T---P-O-S-T-.

  • Comment removed (Score:5, Interesting)

    by account_deleted ( 4530225 ) on Sunday November 02, 2008 @11:19AM (#25603015)
    Comment removed based on user account deletion

  • This proves they're from Chicagoland...
    CTA....
    3 busses will come within 316.86 milliseconds of each other,
    then you'll wait 10,000 years for the next one.

  • Since "emitting" usually has an implied "per second" in it, we should be talking about the power it emits, not the energy.
    • What about the person who emits a "funky odor"? We don't start trying to quantify that little bastard :)
  • It's not mentioned in the article, and I assume it's so obvious that it was ruled out before announcement, but is there anything to suggest that the pulsar is pulsing across all frequencies up to Gamma, and that intervening matter is simply blocking all but the high-energy Gamma portion of the pulse? Or am I just mixing up black-body emission and emission by electron's jumping a band-gap.

    • Re: (Score:3, Informative)

      by glitch23 ( 557124 )

      It's not mentioned in the article, and I assume it's so obvious that it was ruled out before announcement, but is there anything to suggest that the pulsar is pulsing across all frequencies up to Gamma, and that intervening matter is simply blocking all but the high-energy Gamma portion of the pulse?

      Yes it was mentioned:

      This discovery by Fermi is different because it is a purely gamma-ray pulsar. The star is silent across parts of electromagnetic spectrum where pulsars are normally found and hints at a whole population of previously unsuspected pulsars waiting to be picked out of the heavens.

      • Re: (Score:2)

        by EdZ ( 755139 )
        My point was: did they merely not DETECT wavelengths other than Gamma, or have they shown that wavelengths other than Gamma are not EMITTED? No mention is made of what tests can and/or have been done to determine which is true.

        • Re: (Score:2)

          by ceoyoyo ( 59147 )

          It would have to be some pretty special intervening dust to block everything but gammas. Astronomers usually use radio and infrared to see through dust.

        • As I noted below, there is surely radio emission -- we are just not positioned to see it. The implication is that gamma ray emission originates higher in the pulsar magnetosphere than radio emission, so it paints a broader "beam" on the sky as the pulsar rotates.

    • Re: (Score:2, Interesting)

      by Gil-galad55 ( 707960 )
      The radio emission is believed to come from a small patch near the surface of the neutron star called the polar cap. Hence, to see it, the pulsar has to be aligned just so with the line of sight to the Earth. Gamma ray emission appears to originate at a higher altitute, so there are more orientations of the pulsar with respect to the line of sight where we can see gamma rays. It's a geometrical effect.
  • HULK SMASH!!!

  • So, does this imply anything special? (Score:4, Interesting)

    by Jugalator ( 259273 ) on Sunday November 02, 2008 @12:08PM (#25603355) Journal

    Is there more to this than just a new object? Does it imply that certain models on how pulsars form need to be refined? Gamma rays are also incredibly high energy, what does it imply as for the structure of the pulsar that it doesn't emit lower frequencies?

    What I'm getting at is pretty much that the article seem to just pass this off as a "ok, we have a new kind of pulsar here" without any follow up questions raised. IS there any questions to raise? Does this all fit neatly into what we know about pulsars, and is it easily explained why this one doesn't emit in lower frequencies, and only in a very high energy one?

    I'm also surprised there are so much "junk" like the "yourmumisapulsar" tag and Obama posts, etc. Come on now, this is Slashdot, if I want the other stuff on science stories, I can read Digg. :-(

    • Re: (Score:2, Interesting)

      by play_in_traffic ( 946193 )
      Gamma ray does not in fact imply much about energy (although they can be incredibly high energy). It is just another photon. What it does say is that it comes from a nuclear interaction rather than an electronic transition (electron mediated). This most certainly does say something about the nature of the pulsar that is generating this "beam" of ionizing radiation. Please let me know when you have a new model that accounts for this.

      • Re:So, does this imply anything special? (Score:5, Interesting)

        by Gil-galad55 ( 707960 ) on Sunday November 02, 2008 @01:14PM (#25603845)
        No, gamma rays from pulsars are much higher energy than those associated with nuclear transitions (typical scale: 1 MeV; pulsar emission spectra peak at 1 GeV, 1000 times greater).

        Pulsars have extremely strong electromagnetic fields and are hence able to accelerate electrons up to very high energies. These electrons then scatter low energy photons upwards in energy to the gamma ray regime.

        To answer GP's question, observing radio-quiet pulsars like this on in CTA1 tells us more about the gamma ray emission mechanism. Several different models exist, and the primary difference is where in the pulsar's magnetosphere gamma rays are created. In the polar cap model, gamma rays originate in a small patch near the magnetic pole, the same place as the radio emission. So, if gamma rays predominantly come from the polar cap, we shouldn't see radio-quiet pulsars. Hence, this pulsar favors an emission model with gamma rays from higher altitude, in the so-called outer gaps and slot gaps.

        • Re:So, does this imply anything special? (Score:5, Interesting)

          by Bemopolis ( 698691 ) on Sunday November 02, 2008 @02:31PM (#25604419)
          Well, there should be a gamma-ray line at about 511 keV (0.024 A) in all pulsars, since the polar magnetic field strength generates electron-positron pairs, which then annihilate. This produces a broad line (it's a two-photon process), whic has been observed in other pulsars (iirc).

          What's surprising here is the absence of thermal emission from other plasma in the magnetic field which, as you imply, impacts the pulsar at the magnetic poles to produce heat (and hence light.) The question is then, where is this plasma that we usually see trapped in the pulsars' magnetic field. Since this pulsar is no longer inside its parent supernova remnant bubble, I would argue that that this plasma has just been left behind. Why the general interstellar medium has not somewhat replaced it is a bit of a mystery, but that's why we build telescopes in the first place: to find out.
          • Well, there is clearly enough circumstellar (circumpulsar?) material to generate the pulsar wind nebula detected in X-rays, but as with all collisionless shocks, this material must be tenuous.

      • Gamma ray does not in fact imply much about energy (although they can be incredibly high energy). It is just another photon.

        Huh!? Does Planck's constant ring a bell? ...

        E = h * f

        Gamma rays are very high frequency, hence they're highly energetic.

  • ... we'll discover yet another class of pulsars, known as category WEB20, which emit purely Beta rays. And they reflect stuff!
  • Assuming a Neutron star is actually solely made up of Neutrons ... how does it emit electromagnetic radiation when there's no charged particles? Is it just the minute amount of charged particles that reside that emit the radiation, or is it perhaps charged particles around the star, orbiting violently that emit?

    • Re:Would the Physicists Please Stand Up (Score:5, Informative)

      by Gil-galad55 ( 707960 ) on Sunday November 02, 2008 @01:18PM (#25603877)
      The neutron star surface does emit thermal X-rays because it is hot. However, the electromagnetic radiation originates outside the neutron star, in its magnetosphere.

      Pulsars have extremely strong magnetic fields and rotate anywhere from 1-to-1000 times a second. Just like an electric generator, this produces huge electromagnetic fields, and these accelerate electrons to very high energies indeed. These electrons than bang into photons and give them a large chunk of energy in a process called inverse Compton scattering, and we get gamma rays.

      (This is the so-called leptonic channel; it is also possible some gamma rays are produced via pions, but the origin of the energy is the same: the huge electromagnetic fields generated by this spinning magnetic dipole.)

      • But I still don't see how neutral matter can produce radiation? Thermal radiation occurs because of electrons jumping between energy levels, but in an all neutron soup, there's no jumping (none that I can imagine). Moreover, how can neutron matter produce a magnetic field (I'm probably just missing some known mechanism)? I can see that charged matter interacting with the magnetic field produces radiation (just like the northern/southern lights) but my question is where does that field come from? Is there pe

        • Re:Would the Physicists Please Stand Up (Score:4, Interesting)

          by HungSoLow ( 809760 ) on Sunday November 02, 2008 @03:15PM (#25604747)
          Sorry about replying to my own comment:

          Wikipedia - Neutron Star [wikipedia.org]

          "On the basis of current models, the matter at the surface of a neutron star is composed of ordinary atomic nuclei as well as electrons."

           It seems as one moves deeper into the star, the more it becomes a pure sea of neutrons. So all the charged matter on the surface, rotating around like crazy, creates the magnetic field which then causes the emission of radiation.

        • Re: (Score:2)

          by PPH ( 736903 )

          Perhaps, a better question would be: Does the thermal radiation emitted from a neutron star originate from the neutrons themselves? If so, through what mechanism? Or is this radiation emitted by the star's surrounding atmosphere (gas cloud) interacting with the star's spinning magnetic field?

          Neutrons, by themselves, do have a magnetic moment [wikipedia.org].

          • Re: (Score:2)

            by gatkinso ( 15975 )

            The star was very hot (as you might imagine) when it collapsed after the super nova event. Not massive enough to form a black hole, the very very dense neutron matter stopped the collapse. All protrons and most electrons (a 1-1 relationship) were squeezed into neutrons forming a solid crust, a liquid "mantle" of neutrons and electrons, and possibly a solid core, but no one really knows what the interior is like.)

            The resultant body is very small - about the same diameter as the Washington DC beltway. It i

        • But I still don't see how neutral matter can produce radiation? Thermal radiation occurs because of electrons jumping between energy levels

          Thermal radiation is solely due to the fact that the object has a temperature. Planck's law describes the spectrum of the radiation emitted by a black body.

          but in an all neutron soup, there's no jumping (none that I can imagine). Moreover, how can neutron matter produce a magnetic field (I'm probably just missing some known mechanism)?

          Indeed. See below.

          I can see that charged matter interacting with the magnetic field produces radiation (just like the northern/southern lights) but my question is where does that field come from? Is there perhaps a neutron --> proton + electron --> neutron reactions that occur on a regular basis with radiation being a byproduct?

          Yes. As you found out yourself, a neutron star is not perfect. There is always a small percentage of protons and electrons, mostly in the surface crust. As the neutron star is rapidly spinning, this creates a strong magnetic field.

          • A gas of neutrinos, no matter how hot, should not emit blackbody radiation simply because neutrinos do not couple to photons. Oh, they do indirectly (through a W or some such), but that's gonna be a much higher order process and not particularly significant.

      • Re: (Score:2)

        by gatkinso ( 15975 )

        Matter falling onto the stars surface, getting all combobulated, and the resulting radiation from the combobulation shot out at the magnetic poles (which are rotating on a different axis than the star iself) is basically how I remember it from long ago.

        Admittedly, some minor details are being glossed over.

        But actually, "combobulated" is not a bad summary of the series of lectures in a long ago Astronomy 201 class that covered pulsars.

  • The pulsar, which formed in a supernova explosion about 10,000 years ago, emits 1,000 times the energy of our sun.

    Talk about Global Warming!

  • To be that hot, that it only shines in gamma, what could it be made of?
    Obviously it is some form of degenrate matter, but can a quark-star get that hot?
    Does this level of heat, require a size so small that a quark-star is not suffiecient?

    Just wondering, does anyone have a calc as to how hot something realatively-big like
    a nuetron star should be vs. how hot something much smaller like a quark-star should
    be? Can we measure the size of the beam source by some means?

    • To be that hot, that it only shines in gamma, what could it be made of? Obviously it is some form of degenrate matter, but can a quark-star get that hot? Does this level of heat, require a size so small that a quark-star is not suffiecient?

      Just wondering, does anyone have a calc as to how hot something realatively-big like a nuetron star should be vs. how hot something much smaller like a quark-star should be? Can we measure the size of the beam source by some means?

      Why do you assume that the gamma-ray radiation is thermal, which it in fact is not.

  • Comment removed based on user account deletion

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