New Class of Pulsars Discovered

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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So, does this imply anything special?

[Jugalator]

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:So, does this imply anything special?

[play_in_traffic]

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:Emitted or recieved

[Gil-galad55]

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.

Re:So, does this imply anything special?

[Gil-galad55]

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?

[Bemopolis]

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.

Re:Would the Physicists Please Stand Up

[HungSoLow]

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.