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Milky Way Harbors Less Mysterious Dark Matter Than Thought

Oct 13, 2014 10:16 PM EDT
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Our Milky Way galaxy harbors a lot of dark matter, but new measurements show that there is actually half as much of the mysterious substance as previously thought, according to a new study.

(Photo : ESO/L. Calçada)

Our Milky Way galaxy harbors a lot of dark matter, but new measurements show that there is actually half as much of the mysterious substance as previously thought, according to a new study.

Dark matter is the invisible mass that accounts for certain gravitational effects in the solar system - an idea long ago proposed by astronomers. Some 100 years ago, before its existence was even known, yet alone proven, British astronomer James Jeans developed a technique for measuring the mysterious matter - a technique still being used to this day.

Australian astronomers behind the new study used this method to discover that the weight of dark matter in our own galaxy is 800,000,000,000 (or 8 x 1011) times the mass of the Sun. Though this may seem like an extraordinary amount, it's still half of what scientists had predicted. Also, for the first time, the researchers probed the outer edge of the Milky Way, which is situated about five million billion kilometers from Earth.

"Stars, dust, you and me, all the things that we see, only make up about four percent of the entire Universe," astrophysicist Dr. Prajwal Kafle, from The University of Western Australia, said in a statement.

"About 25 percent is dark matter and the rest is dark energy," he added.

Given the mysteriousness of this matter, it's no wonder that its measurements were a bit off. But after Kafle and his colleagues studied the speed of stars throughout the galaxy, including its outer fringes, they helped solve a mystery that has been haunting theorists for almost two decades.

"The current idea of galaxy formation and evolution, called the Lambda Cold Dark Matter theory, predicts that there should be a handful of big satellite galaxies around the Milky Way that are visible with the naked eye, but we don't see that," Kafle explained.

"When you use our measurement of the mass of the dark matter," he added, "the theory predicts that there should only be three satellite galaxies out there, which is exactly what we see; the Large Magellanic Cloud, the Small Magellanic Cloud and the Sagittarius Dwarf Galaxy."

The findings were published in The Astrophysical Journal.

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