Dark Matter Not So Clumpy After All

Dark matter, the mysteriously invisible substance that makes up about 27 percent of the mass in the universe, may not be as clumpy as scientists previously thought. In 2013, researchers with Europe's Planck mission, which studied the oldest light in the universe, found that dark matter has lumped together over time through gravitational attraction. What started out as a smooth and even distribution of dark matter slowly formed dense chunks over time.