Starship Asterisk*

by **FieryIce** » Tue Feb 19, 2008 2:16 pm

Just a suggestion when posting images for discussion on a forum would be to re-size the image smaller or for the really large images just a link works. That would be courteous not only for bandwidth but for ease of reading the posts.

by **neufer** » Mon Feb 18, 2008 9:52 pm

Pete wrote:a couple of online papers (and Wikipedia) mention that Rayleigh-Taylor instability gives rise to the Crab Nebula's filamentary "RT fingers" as the pulsar wind catches up with and accelerates the slower-moving supernova ejecta.

A Rayleigh-Taylor instability of "steam below ice" may be responsible for a sort of "twin of the crab nebula" :

http://antwrp.gsfc.nasa.gov/apod/ap070128.html

Hyperion passes within just 42,000 km of Titan (Mass = 0.0225 Earths) every 64 days. The tidal stresses on a chaotically rotating Hyperion from Titan are almost half what the tidal stresses on Io from Jupiter are (though the Hyperion stress cycle is much less frequent). These Titan tidal stresses probably generated an extremely exaggerated form of "Enceladus Ice Geysers"

http://antwrp.gsfc.nasa.gov/apod/ap071013.html

to the point where Hyperion was left hollow and pock marked.

by **iamlucky13** » Mon Feb 18, 2008 5:58 pm

Kim wrote:Stunning image. Looking closer I see an odd shape in the fine blue haze (I assume that it is part of the neb) it looks rathe like a couple of brackets thus ( )) it seems to be situated at the logical position of the pulsar, so I am wondering if it is a function of the star itself or just an illusion?

Also, I am assuming that the pulsar is the light source for the nebula, how does a city sized star light stuff up 10 LY away? It intrinsic brightness/heat/gravitational energy must be incredible.

I can't figure out which feature you're noticing among all the intricate filaments. Any chance you can post a copy of the image with those features circled or arrowed?

Don't be deceived by the size of the star. Pulsars are extremely active and the radiation they emit heats the surrounding gas.

http://en.wikipedia.org/wiki/Crab_nebula#Central_star

by **neufer** » Mon Feb 18, 2008 2:38 am

Pete wrote:
neufer wrote:
orin stepanek wrote:http://apod.nasa.gov/apod/ap080217.html
WAhat causes the filaments in a nova like this?
Orin
More of that "fur" again. Synchrotron radiation means magnetic field lines.

http://fuse.pha.jhu.edu/~wpb/hstcrab/hstcrab.html

<<Although this is a complicated region of filaments, you can see a number of "fingers" of material that point more or less toward the lower left in this picture. These fingers are dense filaments of gas and are pointing back roughly toward the central pulsar. We believe these fingers are dense regions of gas held in position by strong magnetic fields which are trying to hold out against the expanding bubble of hot gas created by the pulsar.>>
That link doesn't mention it, but a couple of online papers (and Wikipedia) mention that Rayleigh-Taylor instability gives rise to the Crab Nebula's filamentary "RT fingers" as the pulsar wind catches up with and accelerates the slower-moving supernova ejecta. Is that explanation completely at odds with the one at your link?

I don't think it is different(; though I may be wrong).

These plasmas are so tenuous that their individual ions would pass right through each other (like stars in colliding galaxies) if it weren't for the fact that each plasma contains embedding magnetic field lines that prevent that from happening. Magneto Hydrodynamics of plasmas include many bizarre types of instabilities but also normal incompressible fluid instabilities like Rayleigh-Taylor (which this likely is). In any event, the long "furry threads" are concentrations of BOTH matter & aligned magnetic fields.

P.S., Be sure to check out the following if you haven't already
http://www.aip.org/history/mod/pulsar/pulsar1/01.html

by **Pete** » Mon Feb 18, 2008 2:00 am

neufer wrote:
orin stepanek wrote:http://apod.nasa.gov/apod/ap080217.html
WAhat causes the filaments in a nova like this?
Orin
More of that "fur" again. Synchrotron radiation means magnetic field lines.

http://fuse.pha.jhu.edu/~wpb/hstcrab/hstcrab.html

<<Although this is a complicated region of filaments, you can see a number of "fingers" of material that point more or less toward the lower left in this picture. These fingers are dense filaments of gas and are pointing back roughly toward the central pulsar. We believe these fingers are dense regions of gas held in position by strong magnetic fields which are trying to hold out against the expanding bubble of hot gas created by the pulsar.>>

That link doesn't mention it, but a couple of online papers (and Wikipedia) mention that Rayleigh-Taylor instability gives rise to the Crab Nebula's filamentary "RT fingers" as the pulsar wind catches up with and accelerates the slower-moving supernova ejecta. Is that explanation completely at odds with the one at your link?

by **neufer** » Sun Feb 17, 2008 6:30 pm

zbvhs wrote:What's the overall structure of the nebula? Spherical? Ellipsoidal? Is the prominent dust lane running in toward the center of the view on the "front" side of the nebula from our point of view?

Ellipsoidal with the long axis defined by the pulsar jets.

http://www.aip.org/history/mod/pulsar/pulsar1/01.html
http://www.fas.org/irp/imint/docs/rst/Sect20/A6.html

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by **neufer** » Sun Feb 17, 2008 4:47 pm

orin stepanek wrote:http://apod.nasa.gov/apod/ap080217.html
WAhat causes the filaments in a nova like this?
Orin

More of that "fur" again. Synchrotron radiation means magnetic field lines.

http://fuse.pha.jhu.edu/~wpb/hstcrab/hstcrab.html

<<Although this is a complicated region of filaments, you can see a number of "fingers" of material that point more or less toward the lower left in this picture. These fingers are dense filaments of gas and are pointing back roughly toward the central pulsar. We believe these fingers are dense regions of gas held in position by strong magnetic fields which are trying to hold out against the expanding bubble of hot gas created by the pulsar.>>

by **zbvhs** » Sun Feb 17, 2008 3:12 pm

What's the overall structure of the nebula? Spherical? Ellipsoidal? Is the prominent dust lane running in toward the center of the view on the "front" side of the nebula from our point of view?

by **orin stepanek** » Sun Feb 17, 2008 1:28 pm

http://apod.nasa.gov/apod/ap080217.html
WAhat causes the filaments in a nova like this?
Orin

by **FieryIce** » Sun Feb 17, 2008 12:00 pm

That image was taken back in October 1999, January 2000, and December 2000. Has there been a consensus as to the distance to the Crab Nebula; it seems to vary from 6000 ly to 6500 ly. Art, the chart does not have the distance to the Crab listed. If the light from the explosion was seen in 1054 AD, the actual event happened much earlier.

by **neufer** » Sun Feb 17, 2008 11:51 am

Bubblecar wrote:It's a very expressive photo, & they're right to call the Crab a "mess" - it looks like a huge, splattered puddle of cosmic puke

It's even Messier than that!
---------------------------
http://seds.org/messier/m/m001.html
<<The supernova was noted on July 4, 1054 A.D. by Chinese astronomers as a new or "guest star," and was about four times brighter than Venus, or about mag -6. According to the records, it was visible in daylight for 23 days, and 653 days to the naked eye in the night sky. It was probably also recorded by Anasazi Indian artists (in present-day Arizona and New Mexico), as findings in Navaho Canyon and White Mesa (both Arizona) as well as in the Chaco Canyon National Park (New Mexico) indicate; there's a review of the research on the Chaco Canyon Anasazi art online. In addition, Ralph R. Robbins of the University of Texas has found Mimbres Indian art from New Mexico, possibly depicting the supernova.>>
---------------------------

http://www.astronomy.pomona.edu/archeo/ ... ebula.html
<<Every 18 1/2 years, the moon and earth return to approximately the same positions they had on July 4, 1054. If you happen to be in Peñasco Blanco around this time, situate yourself with a telescope under that shelf of West Mesa and look up in the sky. Wait until the moon is in a position pointed to by the fingers of the hand. And then use the diagram under the shelf to position your telescope at the large star in the petrograph. Look in your telescope, and you will see the Crab Nebula.>>

Code: Select all

Mon 1054 Jul 4 12:00 UTC
http://www.fourmilab.ch/cgi-bin/Solar

.                  Right                   Distance    From 36°N 108°W:
.               Ascension    Declination      (AU)   Altitude Azimuth
Sun          7h 14m 29s   +22° 27.3'     1.016    -0.904 -118.924 Set
Crab         5h 34m 30s   +22° 01.0'
Moon         3h 48m 55s   +20° 42.8'   59.1 ER    38.035  -89.239 Up

by **Bubblecar** » Sun Feb 17, 2008 9:22 am

The nebula shines due to synchrotron radiation, the source of the particles being the pulsar wind. However, the exact mechanics of the situation have been a matter of debate. There's a paper discussing various models here:

http://arxiv.org/PS_cache/astro-ph/pdf/ ... 2512v2.pdf

It's a very expressive photo, & they're right to call the Crab a "mess" - it looks like a huge, splattered puddle of cosmic puke

by **Kim** » Sun Feb 17, 2008 8:51 am

Stunning image. Looking closer I see an odd shape in the fine blue haze (I assume that it is part of the neb) it looks rathe like a couple of brackets thus ( )) it seems to be situated at the logical position of the pulsar, so I am wondering if it is a function of the star itself or just an illusion?

Also, I am assuming that the pulsar is the light source for the nebula, how does a city sized star light stuff up 10 LY away? It intrinsic brightness/heat/gravitational energy must be incredible.

Starship Asterisk*

Crab Neb (APOD 17 Feb 2008)

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