In keeping with the stargazing topics that have been our focus this week, today we're going to start with my favorite naked-eye astronomical object: the Pleiades.
It's also known as the Seven Sisters; in Greek mythology, the seven brightest stars (about all you can see without a telescope, even if you have good vision) represented the seven daughters of the Titan Atlas and the Oceanid nymph Pleione. Where I live they're visible in the winter; I love seeing them glittering in the black sky on cold, clear nights.
The Pleiades are mostly hot type-B stars, and the whole group is about 444 light years from Earth, making it one of the closest star clusters. Stars of this class are so energetic that they have relatively short life spans. It's estimated that the Pleiades formed about a hundred million years ago from a cloud of gas and dust similar to the Orion Nebula; already the energy output of the individual stars is blowing away the shroud of material from which they were formed, resulting in the halo-like "reflection nebulae" you see surrounding them.
They're also moving away from each other, leaving the "stellar nursery" in which they were born. In another couple of hundred million years, they will have separated widely enough that future astronomers (assuming there are any around) will have no obvious way to know they started out in the same region of space. Plus, the biggest and brightest of them will already be approaching the ends of their lives, exploding in the violent cataclysm of a supernova, leaving behind a rapidly-rotating stellar remnant called a neutron star, spinning like a lighthouse beacon to mark the spot where a star died.
The reason all this comes up is some recent research into the composition of the stellar nursery where the Sun formed. Because it, after all, was born the same way; along with a number of siblings, it coalesced in a massive cloud of hydrogen and helium, with a few heavier elements thrown in as well. When you look up into the night sky, any of the stars you see could be one of the Sun's sibs. It's impossible, from where science currently stands, to tell which ones. They've all undoubtedly traveled a long way away from their point of origin in the 4.6 billion years since they formed.
But the research, which appeared in the Monthly Notices of the Royal Astronomical Society, uncovered a bit more about what our star's stellar nursery was like. These formations do have some significant differences -- some are small and quiet, with only enough material to form a few stars, while others are enormous and violently active (such as the aforementioned Orion Nebula). In particular, the models of stellar formation suggest that the two different environments would influence the quantities of heavier elements like aluminum and iron. By measuring the amounts of these elements in meteorite fragments that are thought to be leftover material from the formation of the Solar System, the researchers concluded that the Sun formed in a high-energy intense environment like the Orion Nebula, swept by gales of dust and hammered by the shock waves of supernovae.
What a sight that would have been. (From a safe distance.)
So next time you see the Pleiades or Orion's Belt, think about the fact that our calm and stable home star was born in a rough neighborhood. Lucky for us, it's grown up and settled down a little. As beautiful as the Pleiades are, I don't think I'd fancy living there.
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