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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.'"
There was a recent Slashdot discussion on music from pulsars which didn't get quite the attention I wish it did. Along those lines, I'd again encourage all nerds here to check out Gerard Grisey's work Le Noire d'Etoile for six percussionists. This work is based in part on the periodicity of a certain pulsar, and at one moment the performers pause while the sound of another pulsar is acquired with a radio telescope and relayed over speakers in the hall. This would definitely appeal to the many nerds here with an astronomy bent, but it sadly remains little-known outside of IRCAM circles.
No natural object is spinning that fast.
You are obviously not aware about the United States forefathers in their graves, knowing what is going on in that nation.
It is dangerous to be right when the government is wrong.
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.
To follow knowledge like a sinking star, / Beyond the utmost bound of human thought. ("Ulysses", Tennyson)
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.)
To follow knowledge like a sinking star, / Beyond the utmost bound of human thought. ("Ulysses", Tennyson)
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.
"I guess the moral of the story is, don't paint your airship with rocket fuel." -- Addison Bain
Sorry, its high luminosity is more than offset by its distance of kiloparsecs. The relevant quantity is flux, which goes like luminosity/distance^2.
To follow knowledge like a sinking star, / Beyond the utmost bound of human thought. ("Ulysses", Tennyson)