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Pleiades Star Cluster. Photo: NASA, Palomar Observatory
Pleiades Star Cluster. Photo: NASA, Palomar Observatory

Natural Selections: the Pleaides

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The Greeks called them "The Seven Sisters," but a look at the Subaru logo shows the Japanese saw them differently. This familiar star cluster constellation actually contains thousands of stars when viewed through a telescope, as well as brown dwarf proto-stars and dust nebulae and newly-forming solar systems. Martha Foley and Curt Stager look at the night sky.

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The cluster of stars known as the Pleaides has been noted by a variety of cultures throughout history. Researchers today have been able to examine this group of stars with telescopes and determine that it is made up of hundreds of stars, one of which is currently in the process of forming a solar system similar to our own.

“Different cultures through the ages have noticed them because they’re about as noticeable as the Big Dipper,” said Dr. Curt Stager of Paul Smith’s College. To casual observers, this group of stars can look like a blur in the sky. “Back when I was a teenager, when my eyesight was better, my friends and I used to compete: ‘how many can you see?’” said Stager, who could see six or seven stars at that time.

Historically, most cultures saw seven stars in the cluster. The Greeks referred to them as “The Seven Sisters,’ but added two parents to the count to total nine stars. A Hindu subculture claimed that there were six. Stager said, “In fact, if you get out the binoculars and look close, or if your eyes are really good, there’s lots and lots in there.” According to Stager, there are hundreds if not thousands of stars visible in the cluster.

However, the multitude of stars is not responsible for the blurriness of the Pleaides; it is caused by a big cloud of dust. Stager said, “If you look with a really, really, really good telescope, or like the Hubble telescope, you can see this kind of misty cloud background to it that’s sort of blue-ish. That’s dust and other molecules and stuff that are scattering the light of these stars.” Some people refer to them blue stars while others claim that they’re blue because of the scattering effect of the particles.

“A lot of folks thought, ‘well, this cluster of stars must have just been born in that dust cloud, and that’s why they’re all together there,’” said Stager. “Consensus is that they’re relatively young compared to stars, but it turned out, when people looked with really, really good telescopes and you could kind of see the motions, the cluster of stars is moving across the sky and the dust cloud’s going in another direction.” This means that the overlap of the stars and the dust cloud is coincidental.

Telescopes have enabled observers to see into the Pleaides more clearly than anyone observing with the naked eye can. “Some of these things aren’t very bright,” explained Stager. “There’s things called Brown Dwarves that are also in that mix, and those are kind of cool. They’re sort of between a planet and a star.” They are larger than Jupiter, but are considerably smaller than the sun. As a result, their own gravity is not enough to compress them and cause enough heat and pressure in their center to ignite and turn them into a real star. They burn enough to cause a faint glow.

“And then there is one star, if you look really close, that has a dust cloud of its own, and it’s like really, really, really dusty and has chunks of space debris surrounding it that’s not related to that other big cloud,” said Stager. When people examine this star closely, they can see that there are small, rocky planets around the star that are similar to our solar system.

“People are thinking that that star is making its own little solar system and the reason the dust is in there is kind of like what happened to our solar system. When it was first forming, there were all these chunks flying around colliding and smashing up to make all this space debris,” said Stager. While some of these planets are broken into dust, others collect debris and grow larger.

“It’s kind of neat as a scientist to try to tie the scientific facts to cultural perceptions,” said Stager. The ancient Mayans called the Pleaides “the rattle snake tale.” They believed that they came from the Pleaides. “It is kind of ironic to find a parallel there from the science world that you have planets like ours forming, or possibly like ours forming, in the Pleaides,” said Stager. Scientists still have much to learn about this cluster of stars.

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