This is an excellent choice, and (of course) congratulations to the recipients. Their work really did add an extremely significant chunk to our understanding of the universe. And I think it has now been long enough to confirm that their observations really were accurate.
It was also, I think, the first scientific paper I actually read -- I did an assignment on it as a callow young undergraduate, and I still remember sitting in Fisher library poring through the text copy of the journal and trying to figure out what was going on.
Since the page doesn't actually explain the work, I'll have a go. I'm doing this from memory, so someone correct me if I get something wrong. Basically, they set out to study how the distance of a receding galaxy relates to its redshift (ie the speed at which it's receding). Up to this point we could easily measure the redshift of a galaxy, but not its actual distance.
How do you measure the distance to a galaxy? What they did was to look for Type 1a supernovae. This is a particular subclass of supernovae which always have the same luminosity, because they occur when a previously-stable neutron star goes just over the mass limit and becomes unstable. There's a sufficient number of these going off in the universe in any given week that they make a good "standard candle", so by measuring their brightness you can estimate their distance.
What these guys found was extremely surprising: the relationship between distance and speed was not what we would have expected based on a universe which has been evolving only under the influence of gravity since its birth -- there was an extra term which appears to be accelerating the expansion of the universe over time.
And that, right there, is an amazing fact about the universe which nobody knew fifteen years ago.
SNIa are not quite standard candles, not good enough to by themselves make this measurement. However, experimentally it has been observed that their brightness correlates with how fast they brighten and then fade. This relationship, which is not well understood theoretically, makes it possible to measure how fast they brighten and fade and use this to know how bright they are. The difference between an accelerating and a decelerating universe is too small to be seen without this correction.
Second, what these guys did that no one had done before was to figure out how to find the supernovae. Up until then, the way it was generally done was that someone (generally an amateur astronomer) would notice a bright dot in some galaxy and report it. Then the professional astronomers would use large telescopes to observe it in detail and follow it as it brightened and faded. However, this only works for nearby galaxies that amateurs look at.
The problem is that professional telescopes are scheduled months in advance, but you of course can't know that there will be a SN in a few months time so you can apply for telescope time. What they did was sort of the opposite - by surveying a large number of galaxies with a smallish telescope they would be guaranteed to find a number of actual supernovae. They wouldn't know exactly where, of course, but with a large enough number of surveyed galaxies there would always be a few in some galaxies. They managed to convince the time allocation committees on the large telescopes that it was not a waste of telescope time to give them the time just based on the expectation that they would have something to look at. (I think this was the first time where telescope time was awarded to look at something that would happen in the future... ;-) With this method in place, the number of observed high-redshift supernovae skyrocketed.
It was also, I think, the first scientific paper I actually read -- I did an assignment on it as a callow young undergraduate, and I still remember sitting in Fisher library poring through the text copy of the journal and trying to figure out what was going on.
Since the page doesn't actually explain the work, I'll have a go. I'm doing this from memory, so someone correct me if I get something wrong. Basically, they set out to study how the distance of a receding galaxy relates to its redshift (ie the speed at which it's receding). Up to this point we could easily measure the redshift of a galaxy, but not its actual distance.
How do you measure the distance to a galaxy? What they did was to look for Type 1a supernovae. This is a particular subclass of supernovae which always have the same luminosity, because they occur when a previously-stable neutron star goes just over the mass limit and becomes unstable. There's a sufficient number of these going off in the universe in any given week that they make a good "standard candle", so by measuring their brightness you can estimate their distance.
What these guys found was extremely surprising: the relationship between distance and speed was not what we would have expected based on a universe which has been evolving only under the influence of gravity since its birth -- there was an extra term which appears to be accelerating the expansion of the universe over time.
And that, right there, is an amazing fact about the universe which nobody knew fifteen years ago.