An artist's concept shows a vast halo of dark matter surrounding the disk of our home galaxy, the Milky Way. Dark matter produces no detectable energy but reveals its presence by tugging on visible stars, gas, and other matter. Dark matter, which may take the form of heavy subatomic particles, far outweighs all the visible matter in the Milky Way and the rest of the universe. [ESO/L. Calçada]
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Milky Way Matters
The hazy band of the Milky Way arcs high across the dome of the sky this evening. You need especially dark skies to see it because the winter Milky Way is pretty thin. It represents the glow of the stars toward the edge of the galaxy’s disk. But that part of the galaxy is much more thinly settled than the crowded central regions, which we see during the shorter nights of summer.
A recent study by astronomers in Japan used radio telescopes to map distances to some of the galaxy’s important features. The study found, for example, that the galaxy’s center is a bit more than 26,000 light-years away. That would put it a little closer than many other studies have found.
Comparing these distances to how fast objects are orbiting around the galactic center reveals another important measurement: the Milky Way’s total mass. Most of the mass is in the form of dark matter. It produces no detectable energy, but it exerts a gravitational pull on the matter we can see.
Dark matter accounts for most of the Milky Way — only a small fraction of the galaxy consists of stars, planets, and clouds of gas and dust. And the Japanese study suggested that there’s even more dark matter than revealed by other research.
Like all scientific results, these will need confirmation by other researchers. But they suggest that we still have a lot to learn about the universe — even about our own galactic home.
We’ll have more about the Milky Way tomorrow.
Script by Damond Benningfield, Copyright 2012
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