Starship Asterisk*

tnzkka wrote:Beautifully asymmetric. No spirograph-drawing seen.

Beyond wrote:Well, then i am one of the few. I have never heard of a Calabi-Yau manifold.

The canonical bundle of M is trivial.
M has a holomorphic n-form that vanishes nowhere.
The structure group of M can be reduced from U(n) to SU(n).
M has a Kähler metric with global holonomy contained in SU(n).

These conditions imply that the first integral Chern class c1(M) of M vanishes, but the converse is not true. The simplest examples where this happens are hyperelliptic surfaces, finite quotients of a complex torus of complex dimension 2, which have vanishing first integral Chern class but the canonical bundle is not trivial.

http://en.wikipedia.org/wiki/Vela_Pulsar wrote:

[b][color=#0000FF]The Vela Pulsar and its pulsar wind nebula, [/color][/b]

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<<The Vela Pulsar (PSR B0833-45 or PSR J0835-4510) is a radio, optical, X-ray and gamma-emitting pulsar associated with Vela Supernova Remnant, in the constellation of Vela. The association of the Vela pulsar with the Vela Supernova Remnant, made by astronomers at the University of Sydney in 1968, was direct observational proof that supernovae form neutron stars.

It has a period of 89 ms (the shortest known at the time of its discovery) and the remnant from the supernova explosion is estimated to be travelling at 1,200 km/s. It has the third brightest optical component of all known pulsars (V = 23.6 mag) which pulses twice for every single radio pulse. The Vela pulsar is the brightest persistent object in the high energy gamma ray sky.

In early 1970, Curtis proposed the presence of a planetary companion to explain certain variations observed in the pulsar's timing. The putative object would have a mass of about 0.01 Solar masses (i.e., 10 times the mass of Jupiter) and orbit the parent star at a distance of 0.3 Astronomical Units.>>

http://en.wikipedia.org/wiki/Vela_X-1 wrote:

[b][url=http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/full/2008/47/aa09956-08/aa09956-08.html]Figure 1[/url] [color=#0000FF] While Vela X-1 is by far the brightest [20 keV to 800 keV X-ray] source in the field-of-view of ISGRI, we also detect 4U 0836-429 as a very prominent source reaching about a third of the average intensity of Vela X-1, and the relatively weak [20 keV to 800 keV X-ray] sources H 0918-5459, the Vela Pulsar.[/color][/b]

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<<Vela X-1 is a pulsing, eclipsing high-mass X-ray binary (HMXB) system, associated with the Uhuru source 4U 0900-40 and the supergiant star HD 77581. The X-ray emission of the neutron star is caused by the capture and accretion of matter from the stellar wind of the supergiant companion.

The orbital period of the system is 8.964 days, with the neutron star being eclipsed for about two days of each orbit by HD 77581. The spin period of the neutron star is about 283 seconds, and gives rise to strong X-ray pulsations. The mass of the pulsar is estimated to be at least 1.88±0.13 solar masses. Long term monitoring of the spin period shows small random increases and decreases over time similar to a random walk. The accreting matter causes the random spin period changes.

Vela X-1 should not be confused with the isolated radio pulsar, Vela X, which is a very different kind of object. Vela X is associated with a very strong 100 MeV gamma-ray source, which corresponds to a rather weak Uhuru X-ray source, 4U 0833-45.>>

neufer wrote:What this APOD illustrates, IMO, is the complex elegant path this bright object makes on the wide field LAT camera's detector over a long period of time. (Not unlike: http://apod.nasa.gov/apod/ap120121.html )

Chris Peterson wrote:
Ah... I misread things and took this to be where the camera points in the sky. So I'll agree that any particular source (in this case the Vela pulsar) is unlikely to ever be in exactly the same place on the focal plane. I don't think that's remotely the point of the image, however. What it illustrates, if anything, is how much time this object spends on the camera's detector despite the complex path it follows over the sky.

http://en.wikipedia.org/wiki/Fermi_LAT#Large_Area_Telescope_.28LAT.29 wrote:
The LAT's field of view is large, about 20% of the sky.

ronavoig wrote:At first glimpse it reminded me of a Calabi–Yau manifold.

Spin Dizzy wrote:How is the gamma ray energy generated if the neutron star is no longer burning fuel? Is it like a black hole's Hawking radiation where matter/energy is being sucked in, mangled and blasted out as gamma energy? Or perhaps stored energy from before its collapse that's now bleeding out?

neufer wrote:The diagram shows where the Vela Pulsar is located vis-a-vis as to where the LAT camera is aimed and how the camera is oriented (at least, when the Vela Pulsar is NOT located in the center of the field of view). Given the complexity of the pattern it is unlikely that LAT is EVER looking in precisely looking the same direction with the same orientation.

Spin Dizzy wrote:
How is the gamma ray energy generated if the neutron star is no longer burning fuel? Is it like a black hole's Hawking radiation where matter/energy is being sucked in, mangled and blasted out as gamma energy? Or perhaps stored energy from before its collapse that's now bleeding out?

Chris Peterson wrote:
A pulsar is a rotating neutron star. Neutron stars are inert; they have no fuel left to burn and are, therefore, stable. The stars are incredibly dense (although they may have a fluid surface), and have very strong gravitational fields, which hold them together against centripetal breakup. The theoretical maximum speed of rotation for a neutron star (pulsar) is around 1500 rotations per second, although they probably can't get much above 1000 rps in practice because of energy loss by gravitational radiation. Many pulsars are known that rotate hundreds of times per second.

http://en.wikipedia.org/wiki/PSR_J1748-2446ad wrote:
<<PSR J1748-2446ad is the fastest-spinning pulsar known, at 716 Hz. This pulsar was discovered by Jason W. T. Hessels of McGill University on November 10, 2004 and confirmed on January 8, 2005. It has been calculated that the neutron star contains slightly less than two times the mass of the Sun, which is approximately the same for all neutron stars. Its radius is constrained to be less than 16 km. At its equator it is spinning at approximately 24% of the speed of light, or over 70,000 km per second.

The pulsar is located in a globular cluster of stars called Terzan 5, located approximately 18,000 light-years from Earth in the constellation Sagittarius. It is part of a binary system and undergoes regular eclipses with an eclipse fraction of about 40%. Its orbit is highly circular with a 26 hour period. The other object is about 0.14 solar masses, with a radius of 5–6 solar radii. Hessels states that the companion may be a "bloated main-sequence star, possibly still filling its Roche Lobe". Hessels goes on to speculate that gravitational radiation from the pulsar might be detectable by LIGO.>>

Chris Peterson wrote:

copper5817 wrote:Ok, I have a question for you guys. With the pulsar spinning 11 times a second is the density or the gravitational field of the pulsar what keeps the centrifugal forces from flinging material away? Pulsars are know for having extremely dense structures. With this type of density would the structure of the star be hard like a non-porous surface might be? I guess what I'm really wondering is, how much faster can these things spin, and ultimately does the use of the fuel contained within the pulsar eventually contribute to a density loss that would lead to a catastrophic failure of the structure of the pulsar due to centrifugal forces? I imagine that would be spectacular if it did. Kind of like an accretion disk in reverse!

A pulsar is a rotating neutron star. Neutron stars are inert; they have no fuel left to burn and are, therefore, stable. The stars are incredibly dense (although they may have a fluid surface), and have very strong gravitational fields, which hold them together against centripetal breakup. The theoretical maximum speed of rotation for a neutron star (pulsar) is around 1500 rotations per second, although they probably can't get much above 1000 rps in practice because of energy loss by gravitational radiation. Many pulsars are known that rotate hundreds of times per second.

Chris Peterson wrote:

neufer wrote:
I think the purpose is that Fermi is NEVER looking in precisely the same direction with the same orientation.

I don't know what that means. The diagram shows where the camera is aimed; the rotation angle of the camera about the optical axis isn't indicated.

neufer wrote:I think the purpose is that Fermi is NEVER looking in precisely the same direction with the same orientation.

copper5817 wrote:Ok, I have a question for you guys. With the pulsar spinning 11 times a second is the density or the gravitational field of the pulsar what keeps the centrifugal forces from flinging material away? Pulsars are know for having extremely dense structures. With this type of density would the structure of the star be hard like a non-porous surface might be? I guess what I'm really wondering is, how much faster can these things spin, and ultimately does the use of the fuel contained within the pulsar eventually contribute to a density loss that would lead to a catastrophic failure of the structure of the pulsar due to centrifugal forces? I imagine that would be spectacular if it did. Kind of like an accretion disk in reverse!

Chris Peterson wrote:

neufer wrote:
I think the purpose is that Fermi is NEVER looking in the same direction.

Every place on the image where there is an intersection represents a point in the sky where Fermi is looking twice. Given the field-of-view of the camera, what this image demonstrates is that, despite the exotic dance, Fermi spends a lot of time looking at the same places repeatedly.

geckzilla wrote:
Ok, so "never" is a better way of saying "does not always", but I'm not sure it changes the meaning of my post, Neufer.

http://en.wikipedia.org/wiki/Carl_Sagan wrote:
Billions and Billions: <<I never said it. Honest. Oh, I said there are maybe 100 billion galaxies and 10 billion trillion stars. It's hard to talk about the Cosmos without using big numbers. I said 'billion' many times on the Cosmos television series, which was seen by a great many people. But I never said 'billions and billions.' For one thing, it's imprecise. How many billions are 'billions and billions'? A few billion? Twenty billion? A hundred billion? 'Billions and billions' is pretty vague... For a while, out of childish pique, I wouldn't utter the phrase, even when asked to. But I've gotten over that. So, for the record, here it goes: 'Billions and billions.'>>

geckzilla wrote:
So Fermi has to be paranoid and look everywhere. The gamma rays are out to get it.

neufer wrote:I think the purpose is that Fermi is NEVER looking in the same direction.