YouMustBelieve

To do something amazing, you have to be lucky --- and you also have to be prepared. In the latter half of the 1960s Cambridge grad student Jocelyn Bell (aka Susan Jocelyn Bell Burnell) was both. She explains what she did in "Pliers, Pulsars, and Extreme Physics", her 2003 Presidential Address to the Royal Astronomical Society. Bell's radio telescope generated 100 feet of strip-chart recorder paper every day, with the crucial data encapsulated in a squiggly line of red ink. Her initial discovery came after she had scanned miles of wiggles:

A scientist, particularly somebody trained in the physical sciences, has a brain that stores problems, such as things one doesn't understand. Those of us who have trained as physicists have learnt to be economical with our brains. We know that if we understand something we don't need to worry, but if there's something we don't understand, we file it somewhere. In among each 400 feet of chart paper there was occasionally a quarter inch that I did not understand. What niggled me about that quarter inch was that it didn't look like a scintillating quasar, and it didn't look like interference. It was a bit of a puzzle. A further puzzle was that it was intermittent. The first few times I saw this I noted it as a query. But by the second or third time I'd seen this funny, scruffy signal my brain cells were beginning to connect and said "I've seen this sort of signal before. I've seen this sort of signal, from this bit of the sky before, haven't I?" And then it's easy. You get out the charts from previous runs that cover that bit of sky; you spread them out all over the floor so that you can see them, and you realize that yes, you have occasionally seen a quarter inch of signal like that before from that bit of the sky.

The immediate result?

People have asked me "Was it exciting discovering the first pulsar?" No! It was scary and it was worrying. Finding subsequent ones was great, but finding the first one was not. Tony was quite convinced that there was something wrong, that it was an artificial something or other. And of course the place you start is with your own equipment. I had wired up this radio telescope and was scared that I had literally got some wires crossed, that my stupidity was about to be discovered by the combined brains of Cambridge, and I might be leaving without a PhD. ...

But the signal Bell saw wasn't manmade noise, or a glitch in the equipment, or a misinterpretation of something mundane. It was a flicker of energy emitted by a spinning neutron star, the remnant of a supernova explosion. She explains:

So what would a neutron star be like? There's just over 1.4 solar masses jammed in a 10 km radius sphere. The gravitational field is enormous. The work put into climbing Everest on Earth is comparable to climbing 1 cm on the surface of one of these stars. Even light on the surface is bent by the gravitational field, so you can see tens of degrees over the horizon, and clocks run at half the rate they do on Earth. There's also a very strong gradient to the gravity so I wouldn't recommend going to visit a neutron star. The gravitational force on the lower part of your body is so much stronger than on the upper part that "spaghettification" and rupture take place. There's also some very interesting condensed matter physics. In brief, unlike any other kind of star that is a burning ball of gas, a neutron star is like a raw egg. It's got a solid shell on the outside and some very funny gooey liquids on the inside. More technically, the shell is believed to be an iron-56 polymer with a Young's modulus about 106 times that of steel. The very strong magnetic field --- about 108T --- makes the atoms in the star aspherical. The iron atoms lock together like tent poles, producing polymers. The polymers stick together and are incredibly strong. Inside the crust is a region rich in neutrons. Elements that are radioactive here on Earth cannot decay in that regime, basically because beta decay is prevented. Go in a little bit farther and inverse beta decay takes place, so protons and electrons merge to give yet more neutrons and it gets even more neutron rich. Inside that is a layer of neutron superfluid or probably two layers, one being S symmetry, the other being P symmetry. The core of the star we honestly aren't sure about. It may not be the same for all pulsars. Some may be solid, some may be liquid. The Fermi energy is high enough to create bosons so Bose-Einstein condensates are possible. Technically, the Fermi energy is probably high enough to create strange quarks. In short, you have a star 20 km across, weighing the same as the Sun, with immense magnetic and electric fields (108T and 109Vcm-1 respectively) spinning on its axis up to several hundred times per second. This is extreme physics.

There is more. The first planets discovered beyond the solar system were orbiting a pulsar. Why there are planets round a pulsar is another question. The roundest known thing in the universe is the orbit of a pulsar round its companion star. It's round to 1 mm in the radius of the orbit. And if you drop anything on the surface of a neutron star, it hits the deck at half the speed of light. So, these are bizarre objects, hard to believe, but we are forced to believe in them.

That's such a lovely summary of an amazing aspect of the wonderful world that we live in --- a marvelous universe that, thank goodness, forces us to believe in its magic.

(Excerpts from the Fall 2004 issue of Radiations, the newsletter of Sigma Pi Sigma; original article copyright Jocelyn Bell Burnell and Blackwell Publishing; see also FastTimes (11 Sep 1999), RelativityPlusAstrophysics (29 Mar 2000), PulsarWaves (6 Apr 2000), SpinningSources (11 Apr 2000), QpoLmxb (8 Jan 2001), FastForward (21 Feb 2002), ...)


TopicScience - TopicProfiles - Datetag20041228


(correlates: RevolutionsOfAnIrregularSolid, Unknown Knowns, ObserveTheMasses, ...)