[url][/url]That is indeed a stunning time-lapse movie of the Crab Nebula.
I was aware that the network of red Hα filaments was expanding, because stills taken several years apart had demonstrated the expansion. What the movie shows, however, is that most of the outward motion seems to take place in the white synchrotron radiation.
My interest in synchrotron radiation is minimal, but this is what Wikipedia says:
Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when charged particles are accelerated radially, i.e., when they are subject to an acceleration perpendicular to their velocity (a ⊥ v).
Synchrotron radiation is also generated by astronomical objects, typically where relativistic electrons spiral (and hence change velocity) through magnetic fields. Two of its characteristics include non-thermal power-law spectra, and polarization.
A class of astronomical sources where synchrotron emission is important is the pulsar wind nebulae, a.k.a. plerions, of which the Crab nebula and its associated pulsar are archetypal. Pulsed emission gamma-ray radiation from the Crab has recently been observed up to ≥25 GeV, probably due to synchrotron emission by electrons trapped in the strong magnetic field around the pulsar. Polarization in the Crab at energies from 0.1 to 1.0 MeV illustrates a typical synchrotron radiation.
I only understood parts of that, but never mind. A more interesting question is, is the white synchrotron radiation really pushing the nebula outwards, thus making it expand? Or maybe the synchrotron radiation has little to do with the expansion, and it is instead the jets that are responsible for that? But why don't the jets "punch holes" in the nebula and make it all drain away like water in a drain? Is it because the electrons are trapped in the magnetic field of the pulsar?
As a color commentator, I am of course interested in the color of the nebula. In today's APOD it looks like a very tattered Danish flag, which is red and white. Tiny shreds of the green pale of the Italien flag can be spotted at the "bottom" of the nebula.
I have to wonder why there is so much ionized hydrogen glowing red in the nebula, and so little oxygen glowing green. I thought there was quite a lot of oxygen in the supernova remnants of massive stars.
Also, of course, I wonder about the white color of the synchrotron radiation. In many pictures of the Crab Nebula
, the synchrotron radiation looks bluish. Similarly, the jet of supermassive elliptical galaxy M87
is typically seen glowing a "white shade of blue".