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Is the Big Dipper scooping dark matter?

Scientists peered through a galactic window in the ladle of the Big Dipper, using the Herschel telescope to look 10 billion years backwards in time and investigate the origins of galaxies, which turn out to require 20 times less dark matter than previously calculated.

The Big Dipper appears over Charlestown, Rhode Island's Frosty Drew Observatory. Scientists peered through the Big Dipper's Lockman Hole, one of the clearest windows to the ancient universe and found that the amount of dark matter needed to build a young galaxy is far less than previously thought.

Zuma Press/Newscom/File

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IBM's Watson is the new Jeopardy champ? Answer this one, big guy: How much dark matter do you need to build a young galaxy whose rate of star birth is set to overdrive?

Enough dark matter to tip the scales at 5 trillion times the mass of the sun? Last week, right, but this week: Wrong! Try 300 billion solar masses worth of the enigmatic dark stuff.

That's the estimate a team of scientists produced in what lead researcher Asantha Cooray bills as the first attempt to estimate this important quantity in galaxy formation based on observation, and not just through computer simulations.

The number is substantially smaller – as in, almost 20 times smaller – than the estimates computer produced by computer simulations. It implies a gravitational sweet spot that billions of years ago allowed galaxies nestled inside vast halos of dark matter to undergo intense star formation and grow, leading to the zoo of galaxies astronomers observe today.

With too little dark matter, "a developing galaxy would peter out," says Dr. Cooray, an astrophysicist at the University of California at Irvine. The dark matter's gravity would be too weak to counteract the effect of young, hot stars, whose radiation tends to sweep their neighborhoods clean of the gas needed to make additional stars.


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