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Space Science

Resolving Beachballs in the Crab Nebula 123

Posted by timothy
from the only-the-really-active-beachballs dept.
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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Resolving Beachballs in the Crab Nebula

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  • Actually.... (Score:4, Informative)

    by Pharmboy (216950) on Saturday March 15, 2003 @06:29PM (#5521038) Journal
    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.
  • by rexguo (555504) on Saturday March 15, 2003 @06:29PM (#5521039) Homepage
    here's a pic of the Crab nebula: http://antwrp.gsfc.nasa.gov/apod/ap991122.html
  • by cybrpnk2 (579066) on Saturday March 15, 2003 @06:39PM (#5521083) Homepage
    We ran this story with lots of extra URLs earlier this morning here [scifitoday.com]. Get Sci-Fi Today headlines on your Slashdot page by clicking here [slashdot.org] .
  • by Pharmboy (216950) on Saturday March 15, 2003 @06:40PM (#5521088) Journal
    How many of us spent years studying difficult topics in technical fields and learned how to do things because of the "coolness" of some things that we saw as children? I'm guessing that there are a lot of us for whom that was a big motivation for sticking with it when things got hard.

    with all due respect, pulsars (and more) are pretty damn cool as they are. I am not sure how them being the size of a beachball raises their 'cool' level. I agree that 'cool' helps, and get people to go forward at times, but the size just doesn't push it from "almost cool" to "cool enough" for me. I dunno.
  • Re:I thought... (Score:5, Informative)

    by drudd (43032) on Saturday March 15, 2003 @07:17PM (#5521196)
    Yes, but not in the way you're thinking...

    The beachballs aren't the neutron stars, which are somewhere around 20 km in radius. So they weren't a direct result of supernova collapse.

    The beachballs they are observing are the regions of plasma near the magnetic poles of the neutron star which are causing the large bursts of radio waves.

    Doug
  • by Ardias (544478) on Saturday March 15, 2003 @08:02PM (#5521353) Homepage
    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?
  • by zer0vector (94679) on Saturday March 15, 2003 @08:15PM (#5521397)
    You have to understand they are assuming already that this object is a pulsar, which means the pulses are very likely powered by a rapidly spinning neutron star. The energy is emitted constantly but is tightly beamed, so the rotation of the object causes the pulsing. For an object to pulse that fast and to not be spinning faster than the speed of light, the size must be less than the beachball.
  • by Ardias (544478) on Saturday March 15, 2003 @08:35PM (#5521466) Homepage
    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.
  • by zer0vector (94679) on Saturday March 15, 2003 @11:28PM (#5522040)
    I think you might have to look to Occam's Razor on this one. Getting a spinning neutron star isn't very "hard". A asymmetric collapse of a white dwarf does just fine. As well there are mounds of experimental evidence to support a spinning neutron stars. Other interpretations are much more "difficult" to produce, and require vast amounts of energy and extremely strict circumstances for them to occur.
  • by g4dget (579145) on Saturday March 15, 2003 @11:37PM (#5522066)
    Since the subpulses are measured in nanoseconds, that means the beaming region on the pulsar is about that wide.

    Even assuming this very simple geometry and mechanism, it only means that they are 60 cm deep in the direction you are looking at them. Perpendicular to the optical axis, they can be much larger.

  • by ca1v1n (135902) <.moc.cinortonaug. .ta. .koons.> on Sunday March 16, 2003 @02:16AM (#5522545)
    Waves have characteristic "shapes" in both frequency and time domains depending on what created them. A pulse of waves would itself be a wave, and if the output from a pulsar is not a simple sinusoidal wave, it's probably some other form from which a distinct start and end can be determined. There are some forms that come to mind that do not lend themselves to a meaningful determination of start and finish, like exponentials, but those would have infinite energy output anyway, so they're not too likely. The computer simulations they did support these results, and we all know that simulations are always right. So either they've found something new and interesting, or they've found something not so new and interesting that will require them to refine their model of how pulsars work anyway. Either way, something interesting has been learned.
  • by Univac_1004 (643570) on Sunday March 16, 2003 @04:07AM (#5522857) Journal
    its a few nanosecs between pulses, so that is the period. Your comment ignores that.

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