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Pulsars make my brain hurt

January 11, 2010 Leave a comment Go to comments

Pulsars are rapidly, rapidly rotating neutron stars. Neutron stars are what’s left of a massive star after a supernova. They’re hot, dense, and tiny (as far as stars are concerned). The temperature of a neutron star is about a million Kelvin (which is about 2 million Fahrenheit). Compare that to the surface temperature of the Sun, which is only about 11,000 Fahrenheit. They’re onl about 12-14 km in radius, but they’re as have as one and a half to to suns. Imagine a grain of sand, weighing a couple million pounds and hot enough to melt your face off Raiders style. Pulsars do all that, plus they emit beams of electromagnetic radiation, and they rotate fast, really fast.

When pulsars rotate, if their EM beams are pointing towards Earth, it creates a lighthouse effect, except instead of rotating every half minute or so, pulsar beams are emitted every few milliseconds. Even the slowest interval is only 8 seconds. This is what generates the pulse effect that gives pulsars their name. The fastest rotating pulsar that we know about makes 716 cycles, or rotations, each second. Let’s do some quick math. If you take the number of cycles per second, and apply the Fourier transform to it, then plug in Avogadro’s number times the derivative of Schrödinger’s equation… just kidding. We just want to find out how fast a single rotation is, which is just one over 716, or .001399 seconds. We’re taking an average here, and assuming that this pulsar has a radius of 14km, and thus a diameter of 28km. Multiply that by pi and you’ve got the circumference, which is 87.92km (I’m not being consistent with my decimal places, sue me). If you were somehow able to stand on the surface of that pulsar (we’re going to assume a perfectly spherical object and that we’re standing on the equator) you’d be travelling a distance of 87.92 km every .001399 seconds, which is 62,844 km per second or 62,844,000 meters per second. That’s pretty fast, and by ‘pretty’ I mean ‘real damn’ fast. The speed of light is about 300,000,000, which means that this pulsar is moving at about .2 light speed.

Twenty percent of light speed is insanely fast. Considering the mass of these objects, can you imagine the energy expenditure required to get them to move that quickly and keep them rotating that fast? Remember that this is after the lifetime of the star and after a supernova used up a majority of the star’s energy. But this is only one piece of the puzzle that causes my brain to hurt.

The rotational period of pulsars is consistent, amazingly so. Some of them, despite slowing down due to a loss of energy, are as accurate as the atomic clock. Because of the accuracy of their rotations, it’s quite rare to find one that’s inconsistent. After investigating and theorizing on the possible reason behind inconsistencies in a pulsar star’s rotational period, scientists discovered the first extrasolar planets. Any planets orbiting the pulsar would cause an inconsistency in rotation, kind of the way the Earth wobbles thanks to that harsh mistress, Luna. Since any real planets were most likely destroyed by the supernova which creates pulsars, the planets orbiting pulsars are likely remnants of the supernova, and probably just metal rich hunks of rock. Still, they’re planets orbiting stars.

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