Eye-Catching Classes (and Carats)

On Starts With a Bang, Ethan Siegel explains that although we see the full range of spectral classes in the night sky—from cool red M stars to blazing blue O's—75% of nearby stars "are the reddest, coolest, M-class stars, including the closest star to us." Only 4.2 light-years away, Proxima Centauri "is invisible even with binoculars, and even with dark skies, a small, 3" telescope would unable to find it." Yet O and B class stars, despite being much rarer and much more distant, are so luminous that they can't be missed. Brightness can be deceiving—even when looking at entire galaxies and galactic clusters. Ethan adds, "when you're looking for extra-solar planets, don't be surprised that we find the biggest ones and the ones closest to their parent star: that's also bias." Steinn Sigurðsson provides a dazzling example on Dynamics of Cats. It's a giant rock in close orbit around a pulsar, "most likely a pure cold crystalline carbon core of a low mass star, with the rest of the star accreted, blown away and ablated by the millisecond pulsar formation process." In other words, a diamond the size of Jupiter. Or as Steinn says, "10,000,000 trillion trillion carats of hot sparkly rock!"

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