The Planetary Society Blog
By Emily Lakdawalla
Crusty neutron stars
Apr. 25, 2006 | 11:08 PDT | 18:08 UTC
I tend to be interested only in those places in the solar system (or outside it) with solid surfaces, actual places that can be imaged and mapped and -- at least in my imagination -- walked upon. Galaxies and even stars are just too big and too strange for me. So I don't usually pay much attention to the astronomy-related press releases that wander into my inbox. But there's one kind of star that I find fascinating, and that's neutron stars. These are the densest things (short of black holes, for which I don't think it's even possible to define "density") in the universe, and they actually do have solid surfaces, but it's a solid form of a whole different state of matter than we've ever encountered on our relatively lightweight world; the substance of neutron stars is neutrons packed so closely together that the stars are kind of like one giant nucleus of an atom -- neutrons just rubbing shoulders with neutrons. I don't know enough about the physics of the very small to really understand in what ways that kind of matter is strange, but I do know that it's very strange.
So neutron stars are very, very weird, but it appears that you can actually use research techniques that apply to solid bodies made of more ordinary molecular matter to neutron stars. There was a press release this morning from NASA Goddard Space Flight Center that described how a couple of researchers essentially used the techniques of seismology to tease out some facts about the internally layered structure of a neutron star based upon observations of starquakes. Their conclusion: the neutron star in question, a magnetar, SGR 1806-20, has an outer crust "close to a mile deep," out of a total of an estimated 12 miles of the entire neutron star's diameter. (Why they don't report these numbers in metric units, I'm not sure.) They determined this number by observing the frequency with which the star oscillated -- rang like a bell -- after a magnetic "hyperflare" X-ray explosion event triggered a crack in the star's crust, causing a "starquake." It's amazing that we can find out the internal structure of an object 40,000 light years away through anything other than theoretical arguments.
One reason I find neutron stars so interesting is because of a couple of science fiction novels by physicist Bob Forward: Dragon's Egg and Starquake. These books describe life on the surface of a neutron star, and they are fascinating, despite dialogue and characters that are frequently cringe-worthy. That's a minor complaint though; the characters and story are really just window dressing for Forward's soundly scientifically based imaginings of what it would be like to live on the solid surface of a neutron star, and they are pretty mind-boggling. Those books are near the top of my list of favorites.
[By the way, if you buy a book through a direct link to Amazon from this site -- but only if you add it to the cart through that direct link -- The Planetary Society gets a 5% cut.]
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