The Crab with an uncrackable shell

Next Wednesday night, November 28, the Full Moon floats right next to dazzling Jupiter. It’ll be an eye-catching apparition all night long. The orange star just to their right is Aldebaran, the famous alpha star of Taurus the Bull.

Beneath all this brilliant hoopla is Taurus’ most amazing object, even if it is too faint to see without a good telescope. It’s the Crab Nebula and Pulsar: essentially a neutron star. First discovered 45 years ago, neutron stars are the oddest visible objects in the Cosmos.

This story really started before dawn on July 4, 1054, when a new, dazzling star abruptly appeared near the left horn of Taurus the Bull. As bright as Venus, it was duly noted by observers in China and duly ignored in the West, where alterations in the heavens were hard to reconcile with the prevailing theology. Centuries later, telescopes revealed this as the remnant of an exploded star 6,500 light-years away, whose tendrils still rush outward at 1,000 miles a second, visibly altering the nebula every few years.


If it’s weirdness you want, consider that its bizarre glow is not starlight, nor reflected light, nor excited gas. Its origin is neither heat nor nuclear energy. The central glow of the Crab Nebula is an exotic phenomenon called synchrotron radiation, produced when electrons are forced to change direction by superpowerful magnetic fields. This magnetism is a trillion times stronger than what we have here on Earth. It blasts electrons into violent spiraling geysers that produce bits of eerie blue light like yelps of protest.

But this strange lavender glow is just the cloak, the picture frame that surrounds the inner sanctum of strangeness. Now we get to the object that sits heavily at the heart of the nebula, and that creates the magnetic field: the Crab Pulsar.

At first, “pulsar” seems simple enough: It’s a tiny, solid neutron star whose magnetic poles sweep past our line of sight with each rotation. Like a lighthouse, it delivers a quick burst of energy at all wavelengths with every turn. This is the two-solar-mass remnant of what used to be the original giant star’s core. When the rest of the star went kaplooie and exploded outward, this tiny remnant went the other way and collapsed inward.

It spins 30 times a second. Its intense magnetic field acts as a drag, a brake, and slows the wildly spinning star while-U-wait. The Crab pulsar will whirl “just” 17 times a second by the year 4000.

Imagine watching that unfortunate sun blow itself to Kingdom Come a thousand years ago. The shattered star’s core dramatically deflated like a punctured balloon, the material of a half-million Planet Earths packing itself briskly into a ball smaller than Brooklyn. Laws of physics that normally keep objects apart, but fail in places like supernovae and subway cars, allowed this sun that was bigger than our own to collapse down to a radius of only six miles.

Ever-strengthening gravity imploded its atomic contents and fused them into a compressed swarm of neutrons, with some packed leftover protons and electrons elbowing themselves in vain for a little breathing room. “Dense” or “hard” are pathetic understatements. The density of Crab material is the same as a sugar cube containing the steel in every American automobile combined. The star’s density would be exactly duplicated if a cruise ship could be crushed down to the size of the ball in a ballpoint pen — except here there isn’t merely a tiny speck of the stuff, but a sphere 12 miles across containing nothing-but.

Interestingly enough, this is the same density of every atomic nucleus in your body. So in a way, the Crab Pulsar is one huge neutron, 1/200th the width of the Moon.

Most star surfaces are gassy and unsupportive. The Sun’s vaporous photosphere is less dense than water. But unimaginable gravity has forced the Crab pulsar’s broken atom fragments into a kind of lattice, its exterior skin a spherical glasslike structure with a hundred thousand trillion times the stiffness of steel. It doesn’t need to be insured. You couldn’t scratch it with a hydrogen bomb.

A half-mile beneath this impenetrable crust, the star turns liquidy yet gets even denser, but nonetheless boasts a curious super-slipperiness that lets the interior effortlessly spin at a different rate from its surface. At its center only a few miles down, we find a mystery. Our present science comes to an end — right there, dangling just below Jupiter these nights.

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