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Business News/ Opinion / The variation tells the tale
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The variation tells the tale

Why is variation interesting? Because it is the first sign of a possible planet

Photo: Reuters Premium
Photo: Reuters

Driving across the US on a family vacation, we have been subjecting the kids to doses of National Public Radio (NPR). This means we have to occasionally override anguished entreaties for Taylor Swift or One Direction, or a slew of Bollywood tunes we are carrying on a little MP3 device. (Nothing quite like setting the mellifluous strains of Chak De! free to waft across the byways of remote Big Bend National Park in west Texas). Still, there has been enough thought-provoking material on NPR that we hope they won’t hold such overriding against us.

One example, and it even put in mind an earlier journey through west Texas: a discussion about a recent discovery of two planets orbiting a dwarf star just 54 light years away. (That’s rather more remote than Big Bend, but practically next-door when you consider distances in space). Actually, astronomers have known for a while of one planet there, a small one. Using the splendid Lick Observatory in northern California, a team led by a graduate student at the University of Hawaii, Benjamin Fulton, has just found two more. These are several times the size of our Earth, and they zip around their home star several times faster than Earth does around our Sun.

There was a lot to savour and think about in this news. For me, it brought back memories of a charming Lick Observatory evening with the astronomer Raja Guhathakurta, when he told us about the heavens to the strains of Andean music. More to the point, I wondered, how did Fulton and his colleagues actually find these planets? No, it wasn’t via long lonely hours peering through Lick’s telescopes. That rather romantic vision of astronomy is, these days, mostly the domain of serious amateurs.

What professional astronomers do instead, what Fulton and his colleagues did, I got a sense of during a visit a few years ago to another splendid place: McDonald Observatory in the hills of west Texas.

I spent a night there with Dean Chandler, who was using an 82-inch McDonald telescope to search for planets. Chandler had connected his laptop to the telescope, which was aimed at another dwarf star. His purpose: measure the brightness of the star. Every few seconds, readings popped up on his screen, telling the story of that brightness. He pointed out something intriguing—the brightness varied regularly.

Why is variation interesting? Because it’s the first sign of a possible planet. Imagine looking at a distant street lamp around which a bat is flying. As the creature goes round and round, what you see is a bright spot of light (when the bat is behind the lamp), then close to nothing (when it flies between you and the lamp), then the brightness again—on and on like that. In other words, the varying brightness of the lamp suggests that something is flying around it (the bat).

It is much the same with stars and planets that fly around them.

So yes, I could see the variation in Chandler’s numbers. However, his screen also had simultaneous readings from two nearby stars. They remained steady. This helped confirm what astronomers already know about the star Chandler was interested in—that it is a pulsating dwarf. That is, its variation is intrinsic to the star (because it is itself rotating—imagine a lighthouse instead of a street lamp), and not caused by a planet.

What Chandler was really searching for was a variation in the variation. If he found such a second-degree variation, it would strongly suggest a planet there.

Yet, while I could just about see the variation that Chandler pointed out, I could not detect any sign of the second-degree variation. Neither could Chandler, at least not right then.

It is because it is much more subtle, and needs careful and longer-term analysis of the data. As Chandler wrote to me later, “If a planet is there, the variations should come a few seconds earlier or later from year to year over a several year period."

Think of what it might take to detect a several-year pattern like that. “So far we have found strong hints of the second-degree variation," Chandler went on, “but since the planets would be in orbits, the variation should ultimately come back on itself in a complete cycle. We have not yet seen it turn around unambiguously. The amount of delay seems to have stopped climbing, but hasn’t really reversed yet."

The Lick Observatory has an automated planet finder (APF) telescope that Fulton’s team used to find their two planets. My layman’s reading of their analysis of years of data suggests an effort similar to Dean Chandler’s at McDonald: detecting variations, ruling out possible known causes, looking for cycles.

Fascinating stuff, all around. There was even some consolation for the anguished fan in our car. Another NPR segment told us about the scientist Stephen Hawking’s recent suggestion that it is entirely possible that in some alternate universe, Zayn Malik still sings with One Direction.

Question remains, though: how will we detect that particular cosmic phenomenon?

Once a computer scientist, Dilip D’Souza now lives in Mumbai and writes for his dinners. A Matter of Numbers will explore the joy of mathematics, with occasional forays into other sciences.

Comments are welcome at dilip@livemint.com. To read Dilip D’Souza’s previous columns, go to www.livemint.com/dilipdsouza

Follow Mint Opinion on Twitter at https://twitter.com/Mint_Opinion

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Published: 07 May 2015, 04:10 PM IST
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