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Resolving Beachballs in the Crab Nebula
Stranger4U writes "Researchers at New Mexico Tech and the NRAO have used the Aricebo radio telescope in Puerto Rico and some specilized equipment to more closely examine the pulses from the Crab Nebula pulsar. Some of the signals lasted less than two nanoseconds, meaning the originated from a volume no bigger than beach ball. Stories are here(1) and here(2)."
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The article clearly states:
Although it is premature to discount all other possibilities, Kern told UPI, "for now it looks as though the mechanism we propose is probably correct."
"The interpretation here looks appealing," he told UPI, "although further predictions and tests will have to be made for it to carry the day."
It article seems a bit more reserved than the editor posting it. An interesting read tho.
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here's a pic of the Crab nebula: http://antwrp.gsfc.nasa.gov/apod/ap991122.html
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We ran this story with lots of extra URLs earlier this morning here. Get Sci-Fi Today headlines on your Slashdot page by clicking here .
That something so small and so massive would have gone ahead and collapsed into a black hole. Were there multiple beachballs per supernova?
Resolving Beachballs in the Crab Nebula - this has to be the most nonsensical headline I've EVER read!
Did anyone else notice the sheet number of alliterations the author of the first article used? I think someone wishes he weren't a science reporter....
Astronomers have tracked the long-sought source of brilliant beams that bounce across galaxies from super-dense spinning star...
...helps illuminate one of the most exotic environments ever perceived...
...a pulsar spews sprays of radio waves...
...A supernova marks the farewell flicker...
...expelling a great belch that spits the stellar shell into space...
etc...
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Some of the signals lasted less than two nanoseconds, meaning the originated from a volume no bigger than beach ball. That is very presumptuous. There are ways to get around that. It would be possible for larger object to produce pulses much shorter than the time it would take light to travel the distance of its diameter. When a shockwave starts well below the surface of a sphere, and propagates uniformly along a fairly crisp expanding sphere, it could cause the surface to flare up briefly wherever it hits, and the radius of the affected area would expand faster than the speed of light because of the geometry of it. Something like that, only happening in a neutron star, could explain those kinds of pulses without the requirement that they occur in such a small volume.
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These are not separate beachball sized objects within the Crab Nebula. The pulses come from a beachball sized area on the pulsar within the Crab Nebula.
The magnetic field of the neutron star is so strong that it sends out radiation. The points of origin for the radiation are at the north and south magnetic poles of the neutron star. Since the neutron star rotates so fast, the radiation looks like a pulse to us. The surface locations that create those beams of radiation are small, only the size of a beach ball. And the radiation is so strong that it ionizes the atoms on the surface or just above the surface, making a little plasma cloud above the neutron star's magnetic poles.
Light travels across 12 inches in one nanosecond. (Side note: When radio astronomy technicians install optic cables, they have to measure the cables in nanosecond-light-lengths.) Since the subpulses are measured in nanoseconds, that means the beaming region on the pulsar is about that wide. A neutron star is 12 to 20km wide, and astronomers once thought the beaming region was as much as 10% of the surface area. Now, they are surprised to discover it is much smaller.
So, the question now is: what confines the neutron star's very powerful magnetic field to such a small region?
A pulsar does not produce pulses. The "pulse" that we see comes from a steady uniform beam of radiation from a rotating neutron star.
Ever see a lighthouse in action at night? That light is a steady beam from a very strong lamp mounted on a rotating platform. The platform spins at a steady rate. If you are nearby, such as on the ground looking up at the lighthouse, you can see the rotating beam. If you are on a ship, far away at sea, you don't see a rotating beam. Instead the observer on the ship sees a pulse.
The neutron star inside the Crab Nebula spins at a very steady rate of 33 rotations per seconds. It has 2 hot spots, one at the magnetic north pole, and another at the magnetic south pole. These hot spots produce a steady beam of light, which we see as 33 pulses per second.
Now, there are shockwaves produced by by seismic shifts within the neutron star. The neutron star has a crust that breaks into pieces and shifts around occasionally. (Think of earthquakes here, but the crust is very thin, and very dense, so the energy released is much greater than what powers an earthquake around here.) These shifts cause "hiccups" in the radiation beam. We can actually measure these hiccups because the "pulse" goes out of phase for a moment.
But, to finally answer your question, those shockwaves do not cause the "pulses", but merely adjust their timing for a brief moment. Also, a shockwave would be only an occasional event, rather than something that happens 33 times every second like clockwork.
The subpulses within the pulses are also very well timed, to within 2 nanoseconds. Since light travels about 61 cm in 2 nanoseconds, the hot spots that cause the subpulses are at most 61 cm wide.
We still have a few unknowns here, such as what confines the hot spot to such a small region. But, what causes the pulse itself is known.
But just as importantly, all that this seems to tell you is that the region from which these subpulses come is less than 2ft thick along the line from here to there, it tells you much less about its area. So, perhaps this is just the signal you see when looking straight at the neutron star and something happens on a surface pacth. The patch could have a much larger diameter than 2ft.