Newspaper article The Christian Science Monitor

Little Green Men? New Type of Star Breaks All the Pulsar Rules

Newspaper article The Christian Science Monitor

Little Green Men? New Type of Star Breaks All the Pulsar Rules

Article excerpt

Isaac Asimov reportedly said, "The most exciting phrase to hear in science, the one that heralds new discoveries, is not "Eureka!" but "Hmm. That's funny..."

Recently, a group of Swiss astronomers found something very funny indeed: slowly pulsating stars. Pulsating stars, a type of variable stars, typically pulse quickly - from a few times per hour to over a thousand times per second. But these newly discovered stars are brightening only once every two to 20 hours.

"The very existence of this new class of variable stars is a challenge to astrophysicists," says Sophie Saesen, a member of the research team, in a press release.

Not only are these stars incredibly slow, but their pulse is weak: they're only getting only 0.1 percent brighter with each pulse. Spotting such a tiny variation, with such a remarkably slow period, took astronomers years.

"We have reached this level of sensitivity thanks to the high quality of the observations, combined with a very careful analysis of the data," says Nami Mowlavi, leader of the research team, "but also because we have carried out an extensive observation programme that lasted for seven years."

The telescope they used, a Swiss 1.2-metre Euler telescope at the European Southern Observatory's La Silla Observatory in Chile, is too small for most astronomy, which turned out to be a blessing, says Dr. Mowlave, who is based at the Geneva Observatory. "It probably wouldn't have been possible to get so much observing time on a bigger telescope."

For seven years, the research team observed more than 3,000 young stars in the star cluster NGC 3766 for a few weeks each year. They found variable stars - 163 of them - including 36 that seem to break all the rules of pulsars. In fact, they held off on labeling the stars "pulsars," choosing the less controversial label of "periodic variable stars," though they said that they expect the scientific community to confirm that they are, in fact, pulsars.

So what's a pulsar, anyway?

Pulsars, stars whose brightness appears to "pulse" at regular intervals, were first identified in 1967. Almost fifty years later, astronomers still haven't figured out exactly why they pulse, but most agree on this much:

Pulsars are born in supernovae. When a massive star explodes, its core is compressed into a neutron star: a star with no protons or electrons, just an unbelievably dense lump of neutrons, about 10 trillion times denser than lead, spinning incredibly quickly.

Think about a figure skater with her arms outstretched. When she pulls them in, she spins faster and faster, not because she's adding effort, but because the original energy of her spin is now being applied over a smaller radius. Now imagine that she started as a spinning star - a star many times larger than our own sun - and then shrunk down to a rock a few miles across. …

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