By Ron Cowen
New surveys of the sky are examining the two facets of galaxy formation. One focuses on the glitter. The other examines the gloom. A census of both the light and the dark parts of the cosmos is essential for understanding how today’s universe came to be, the scientists say.
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One of the new surveys looks at the panorama of galaxy shapes, masses, colors, and sizes that existed when the cosmos was about half its current age—a critical time when galaxies began to take the form they’re in today. The other survey also sizes up galaxies but uses some gravitational sleight of hand to expose the dark side—the vast concentrations of dark matter that provide the framework for all the visible stars and gas in the universe. Dark matter, though unseen, makes up more than 90 percent of the mass of the universe, theorists say.