Wednesday, February 11, 2009

Intermediate and Massive Stars Conference, Day 2

Yesterday was the second day of a conference here in Strasbourg, France, on intermediate-mass and massive stars. (As a reminder, here we mean stars that are about 5 or 6 times the mass of the sun and larger.)

Yesterday was one of those days that caused my brain to hurt a little, because the topics covered were fairly unfamiliar to me. The majority of talks were on the atmospheres of red giant and red supergiant stars. Stars, like some people, swell up and get rosy-faced as they get old. Exactly why this happens is a matter of quasi-philosophical debate, but when you make a computer model of a star that is using the last of its nuclear fuel, the model wants to swell up.

At any rate, when a star swells up, it cools off from temperatures like that of the sun (10,000 degrees Fahrenheit or hotter) to much cooler temperatures (only 5000 degrees Fahrenheit or cooler). At the same time, the outer layers of the star begin a slow roiling, like bubbling oatmeal, and the surface of the star gets fairly splotchy, with hotter patches, cooler patches, and perhaps even shells of dust and gas surrounding the main star.

When we look at a star, we just see a single point of light, so light from these bright and dark patches and shells of gas and dust all are blended into a single point, and it is the job of the red giant-studying astronomer to try and disentangle this mess.

To make it worse, red giant stars are cool enough that some atoms start to link up and form simple molecules, like carbon monoxide and titanium oxide. These molecules form and dissolve in the cooler and hotter parts of the star, and though they are fairly rare, they tend to absorb a lot of light. Think of it sort of like suntan lotion: a tiny bit of lotion can block almost all of the ultraviolet light from the sun. Now imagine that you are sloppy putting on the suntan lotion, so that you get patches of sunburn scattered among patches of healthy skin. The astronomer would then be like a dermatologist several miles away who is trying to determine how sunburned that distant speck of a person is.

Anyway, I don't work on this aspect of astronomy, so a lot of the techniques, nuances, difficulties, and big questions are unclear to me. And yet yesterday I found myself listening to hours of talks discussing computer models of red giant stars, observations of red giant stars, and other related astronomy. I did my best to learn what I could, and most of the speakers did a very good job of explaining the most important implications of what they were doing. So, even though I didn't follow the details all of the time, I understood why I should care about their work.

In addition to those talks, we also heard about stellar interferometry (which is a technique that allows us to actually measure the size and shapes of many red giant stars), and some new findings on variable red giant stars (stars that are changing their brightnesses). One of the neater findings there is that while we understand why many red giant stars vary their light in a regular manner (Mira-like variables, for those in the know), there are a number of red giant stars that change their light output regularly over much longer timescales than theory would predict. (It's always fun to see an astronomer toss his or her arms up in the air and say, "We don't know what's going on here!")

Today is the last day of the conference. Tomorrow I'll be traveling back to the US, a trip that will take 24 hours from the time I jump in a cab here in France until my plane lands in Austin, so I won't be blogging tomorrow, and I probably won't feel up to it on Friday. We'll see.

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