Starship Asterisk*

MarkBour wrote:The Crab sure seems fascinating. It would have begun as a point (from the view of Earth) in 1054, when we saw first light of the explosion. I was not able to figure out from the Wikipedia articles whether or not it is known what type of supernova was involved (perhaps I did not read them patiently enough). The remnant includes a pulsar which the articles said is a neutron star.

Art described the slowing of the ejected mass above. I don't know how much confidence he has in the various parameters for his estimate.

The synchrotron radiation with its fast-moving ripples is more dramatic than the main ejecta. It represents some of the energy that is coming from the pulsar, which is slowly "spinning down". One article (http://astronomy.swin.edu.au/cosmos/P/P ... ristic+Age) listed:

In 2007 the Crab pulsar had a period of 0.0331 sec and a period derivative of 4.22×10-13s/s.

I wonder how long of a time period for observation was necessary to determine this derivative. Perhaps there is some clever way to do it in a short period of time rather than what would be my first idea of trying to measure the period more or less directly once each year. For such a derivative, one would expect after about 10 years (= 3.15576 E+08 sec) that the rate would slow from 0.0331 sec to 0.03296 sec. Long-term, it seems there's not much chance it would be a linear process, so the derivative would change. Does this sound correct? I gather that a typical pulsar spin-down is a very long process, so it's not like this pulsar will go quiet any time soon.

MarkBour wrote:
Art described the slowing of the ejected mass above.

I don't know how much confidence he has in the various parameters for his estimate.

In 2007 the Crab pulsar had a period of 0.0331 sec and a period derivative of 4.22×10-13s/s.

distefanom wrote:Each time i see this image, I wonder the visual-meaning of the ripples and the stone-in-the-pond effect we see into the movie.
I refer to the "waves" we see in the gas around the pulsar...
I sometimes explained it to myself (as a rookie) like "waves of density" of the expanding gas, but
could it be also a sign of the space-time deformation due to the central neutron star, which is spinning at relativistic speeds?

ems57fcva wrote:
In space, there is no atmosphere, and those gases got thrown out at much higher speeds that a conventional explosion. (A supernova is a star going off like an oversized nuclear bomb after all.) So the gases from the explosion will expand for a very long time, and not stop until it pressure becomes as low as that of the interstellar medium, which is almost a vacuum. If fact, the Veil Nebula is part of the remnant from a supernova than occurred over 7,000 years ago, and which is still expanding.

Ann wrote: ... s 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? ...

Ann wrote: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:

Wikipedia wrote:

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,[11] probably due to synchrotron emission by electrons trapped in the strong magnetic field around the pulsar. Polarization in the Crab[12] 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".

Ann

Wikipedia wrote:

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,[11] probably due to synchrotron emission by electrons trapped in the strong magnetic field around the pulsar. Polarization in the Crab[12] at energies from 0.1 to 1.0 MeV illustrates a typical synchrotron radiation.