Star Struck

November 15, 2008

When people hear I live in Los Angeles, they often assume -- incorrectly -- that I routinely run into celebrities. I have to explain that LA is a big city, and frankly, my lifestyle is such that we just don't run in the same circles as Brangelina or Lindsey Lohan. If they look disappointed, sometimes I'll tell the story of that one time I spied Britney Spears shopping at Barneys or one of the other major stores along Rodeo Drive.

Well, I didn't actually see Britney, per se. I saw her substantial entourage, which included the obligatory gaggle of papparazzi, jostling and angling for the best candid shot of the Troubled Pop Star Shopping for the Perfect Shoes. I knew it was her because the photographers kept shouting her name to get her to look at them, even for just an instant. It was an unexpected glimpse into the interior of a completely different world. But I couldn't say I truly understand what the pop star's day-to-day life is like in great detail, based on that snippet of indirect evidence.

Scientists might not follow Britney's tabloid woes (or if they do, are unlikely to admit it), but they are star-struck when it comes to the cosmos, and for similar reason: the stars are alien worlds, and we are always jostling for the best angle to sneak a peek into their very cores. Stars, you see, are energetic factories for stellar nucleosynthesis, churning out chemical elements from carbon to calcium via nuclear fusion of hydrogen and helium into heavier nuclei. These newly born elements are then dispersed throughout the universe by the solar wind, or as planetary nebulae. Carl Sagan famously observed that we are all made of star stuff. He didn't mean we were all potential celebrities; he meant that we are carbon-based life forms, and carbon first formed in the interiors of stars.

Heavier elements (beyond iron) require far more intense nuclear reactions -- namely, supernovae, which is what massive stars become when their core fuel runs out. The star collapses under the force of its own gravity, its core getting hotter and denser, until it explodes. The intense heat creates those heavier elements, and also helps propel them out into interstellar space to seed the rest of the universe.

And that, my friends, is why life exists at all in our universe. Sagan was right: we are all star stuff, born in the nuclear furnaces of stellar nurseries. And we need all the other stuff, the other elements created in those distant stars, in order to thrive on Earth. The cosmos is one giant ecosystem.

Those papparazzi photos of celebrities skinny-dipping on their vacations, or chilling out at their private estates, or shopping at Barney's, are generally pretty fuzzy in terms of resolution, because they're taken from such a distance. Photographers use all sorts of tricks and expensive equipment, including powerful zoom lenses, to get those scandalous shots that will make their careers.

Similarly, our picture of what's happening in stellar nucleosynthesis is lacking in resolution: we can make out the outlines of the general principles, but the details are still a bit fuzzy. We're studying them from a great distance, after all, and have to rely on indirect evidence (eg, by measuring isotope abundances). Frankly, we can only really observe the outer layers with existing telescopes. Given the fact that inside, the stars are like bubbling, boiling cauldrons, constantly mixing elements together, it's quite possible that we are getting a misleading or incomplete picture of stellar nucleosynthesis.

But how do you look inside a star, when you can't get anywhere near them (whether by virtue of vast light years of distance, or one of those pesky restraining orders)? Ideally, scientists would like some sort of ultra-zoom lens to get more detailed resolution of the interior life of stars. In recent years, they have figured out that they can use certain elements as probes -- fluorine and nitrogen, for example, which respond easily to the "mixing mechanisms" of the stellar interior. The trick is to measure the rate of the nuclear reactions taking place in the nuclei properly. This becomes a problem at very high temperatures, apparently, thanks to the electric repulsion of same charges (opposites attract, like repels like), which acts as a barrier to the probes.

So I was intrigued a few weeks ago by a paper in Physical Review Letters by physicists at Texas A&M University and Italy's LNS laboratory, proposing a sort of "Trojan Horse" scheme to look inside stars. They took their cue from Homer's Odyssey, namely, the siege of Troy and Ulysses' scheme to hide his warriors inside a giant wooden horse presented to the Trojans as a peace offering. Once inside the gates, the warriors waited until nightfall, then emerged, and conquered the unsuspecting city.

Claudio Spitaleri, Robert Tribble and Leontina Banu tried a similar strategy to overcome the barrier of electric repulsion in fluorine and nitrogen probes. They hid the particle that would induce the nuclear reaction inside another nucleus so the repulsion factor didn't kick in and the probes could get inside the star. According to their PRL paper, it worked: they made the first accurate measurements of the rate at which those nuclear reactions take place, rather than relying on various estimates as has been done in the past. And that means astrophysical predictions will be that much more accurate in the future.

Photos: (top) Composite image of Kepler's supernova from images by the Spitzer Space Telescope, Hubble Space Telescope, and Chandra X-Ray Observatory. Source: NASA, via Wikimedia Commons (public domain). (bottom) "Cesium" (one of the heavier elements produced in supernovae), from The Elements series by Nash Hyon. Used with permission.

Comments

[Freiddie]

Nice comparison between stars & stars.