Anders Sandberg wrote:
> Hmm, to get the EMP I guess you need the radiation to interact with a
> suitable magnetic field to bunch it up into an EMP? The galactic
[random online source]
electromagnetic pulse (EMP): 1. The electromagnetic radiation from a nuclear
explosion caused by Compton-recoil electrons and photoelectrons from photons
scattered in the materials of the nuclear device or in a surrounding medium. The
resulting electric and magnetic fields may couple with electrical/electronic systems to
produce damaging current and voltage surges. May also be caused by nonnuclear
means. 2. A broadband, high-intensity, short-duration burst of electromagnetic
energy. Note: In the case of a nuclear detonation, the electromagnetic pulse consists of
a continuous frequency spectrum. Most of the energy is distributed throughout the
lower frequencies between 3 Hz and 30 kHz.
[from elsewhere]
The amplitude, duration and polarization of the wave depend on the location of the
burst, the type of weapon, the yield, and the relative position of the observer. The
electric field resulting from a high-altitude nuclear detonation can be on the order of
50 kilovolts per meter with a rise time on the order of 10 nanoseconds and a decay
time to half maximum of about 200 nanoseconds. It is very fast.
> magnetic field is rather I weak I seem to recall, and then you would
> have to get through both the heliopause and the earth's magnetopause.
Indeed, I was assuming a source energetic enough to penetrate the heliopause
and the geopause (well, it is supposed to be a violent event). Of course, the
braking of charged particles will give a more slowly rising EMP, until the
stream can directly impact the atmosphere.
Somebody stop me before I produce any more nonsense.
> What is the energy density per square meter of a dangerous EMP? I have
> seen talk about terawatt pulses, but it is not clear what the energy
> density is. If we use 50kV and a 200 ms triangular wave, the energy
According to above source, NEMP produces edges of 10 ns duration and
total pulse duration of ~200 ns. How about GRBs? These are short
and bright.
> would be on the order of 1/2 e_0 E^2 * t, or 0.0011 J/m^2. Take that
> and multiply with 4*pi*6.4e7 pc^2 to get the total energy = ~10^40 J
> of electric energy.
>
> That seems to be be between the 6 x 10^{37} joules of Nova Persei
> outburst and the 3 x 10^{41} joules of a 450 km s^{-1} neutron star
> kick (thanks to
> http://physics.hallym.ac.kr/reference/scales/scales1p.html). Hmm,
> actually far less than than I expected. If a type II supernova managed
> to convert its photon energy into EMP with an efficiency of 3e-5, then
> it could do it. Somehow I doubt it would happen though. The fields we
> see in nebulas look quite placid.
>
> What about galactic dynamos like active galaxies with jets? Or
> interstellar masers?
If you'd were to look down the axis of something like
http://www.sciencemag.org/cgi/content/full/291/5501/84
you'd be probably rather shocked, too ;)
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