National Geographic Feature: “Star Struck” by Ken Croswell

An all-sky image of the Milky Way (Serge Brunier/NASA)

An all-sky image of the Milky Way (Serge Brunier/NASA)

As promised, here’s an excerpt from astronomer Ken Croswell’s “Star Struck,” a National Geographic featured article from the December 2010 edition that takes us on a fascinating tour of the Milky Way.

Croswell discusses recent discoveries of hypervelocity stars, why planets are rare in the outermost reaches of our galaxy and the black hole hiding inside the galactic core. The Astroengine article “Life is Grim on the Galactic Rim” gets a mention as Croswell describes metal-poor stars and why life might be unlikely in those systems.

From “Star Struck”:

It’s hard to be modest when you live in the Milky Way. Our galaxy is far larger, brighter, and more massive than most other galaxies. From end to end, the Milky Way’s starry disk, observable with the naked eye and through optical telescopes, spans 120,000 light-years. Encircling it is another disk, composed mostly of hydrogen gas, detectable by radio telescopes. And engulfing all that our telescopes can see is an enormous halo of dark matter that they can’t. While it emits no light, this dark matter far outweighs the Milky Way’s hundreds of billions of stars, giving the galaxy a total mass one to two trillion times that of the sun. Indeed, our galaxy is so huge that dozens of lesser galaxies scamper about it, like moons orbiting a giant planet.

Read the rest of “Star Struck” by Ken Croswell in the December edition of National Geographic.

In addition to the article, National Geographic has a beautiful extended Milky Way gallery that’s well worth a look.

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6 responses to “National Geographic Feature: “Star Struck” by Ken Croswell

  1. “The sun,27,000light years away…”(from the galaxy core)
    “reported an Xray echo some 350 light years from the black hole…” “the echo indicates that an object fell into the black hole around 350 years ago.”
    What happened to the 27,000 years it would take for the light to get here?
    Does anyone fact check or proof-read this stuff?

  2. There’s nothing wrong with this. Astronomers give the time of an event as the time we see it on Earth–e.g., the 1987 supernova in the Large Magellanic Cloud.

    • There’s plenty wrong with it. They’re not stating when the event was seen on Earth–which was in 2004–but specifically when the event happened. The article unambiguously states that an object fell into the black hole 350 years ago. Obviously, that’s wrong. If they wanted to call it “the 2004 X-ray Echo 350 LY from Sag-A*”, great–but they didn’t. Clearly this is a stupid error on NG’s part.

      • No, it’s not a stupid error by National Geographic. It’s how astronomers talk.

        Take a look at the refereed scientific publication on this matter: Revnivtsev, M. G., et al., 2004. Hard X-ray View of the Past Activity of Sgr A* in a Natural Compton Mirror. Astronomy and Astrophysics, 425, L49.

        The abstract states: “We conclude that 300-400 years ago Sgr A* was a low luminosity (L ~ 1.5 x 10**39 erg/s at 2-200 keV) AGN with a characteristic hard X-ray spectrum.”

        Another example: Muno, M. P., et al., 2007. Discovery of Variable Iron Fluorescence from Reflection Nebulae in the Galactic Center. Astrophysical Journal Letters, 656, L69.

        The last page states: “Such an outburst would have occurred 60 years ago, before the advent of X-ray astronomy, and therefore would not have been observed.”

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