Saturday, June 28, 2008

Hunting the elusive voorwerp

Since it's been slashdotted and has appeared on the major news feeds, there's a good chance you've heard of Hanny's Voorwerp by now. It's a we-haven't-seen-anything-quite-like-this found by a Dutch schoolteacher named Hanny as part of the Galaxy Zoo project (I've seen voorwerp variously translated as "object" or "thing" -- the etymology suggests there might be a shade of meaning we're missing, so better not to translate).

The Galaxy Zoo is an interesting bit of crowdsourcing. Unlike SETI@home, GIMPS or similar projects it relies on human processing power rather than the idle cycles of millions of PCs. In the typical distributed-computing project, the algorithms are well-understood but require massive amounts of computing power. In this case, no one knows a good algorithm for classifying galaxies, but people can do it reasonably well, even with no training in astronomy.

Galaxy Zoo literally gives the rest of us a look at what kinds of things astronomers spend their time looking at, plus the chance of turning up something truly new. It also relieves the astronomers of the effort of taking a first look at millions and millions of images and turns up oddities, like the voorwerp, that would otherwise have gone unnoticed. Going by the entries on the Galaxy Zoo blog and the acknowledgments in the submitted papers, they're very grateful for the assist.

Apart from the human visual system's ability to recognize shapes, Galaxy Zoo takes advantage of another facet of human perception, namely its imprecision. While most people could easily distinguish a well-defined spiral galaxy from an elliptical one, many actual galaxies are harder to characterize.

In such cases a particular algorithm distributed to everyone's PC would always give the same answer, whether it's right or wrong. With some effort, you could distribute several different algorithms [or several versions of the same one, or one with some random "fuzz"] and look for discrepancies, but you'd have to write several different algorithms, or at least discover tuning parameters that made a significant difference. This not impossible, by any means, but you get it for free by having several people look at the same image (or, quite possibly, just from having the same person look at the image every so often).

Objects that produce varying answers are likely to be the interesting borderline cases, whether because there's more going on with them, or simply because we humans have more trouble figuring it out.

[Hanny's Voorwerp has since been identified as a "quasar ionization echo", but there's still plenty of research to be done.  Similar objects (voorwerpjes, or "little voorwerps") have been found elsewhere.  As usual, Wikipedia has a summary -- D.H. Dec 2018]

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