The Universe just had its temperature taken, and the results may surprise. Since the 1990s, researchers have put forth the theory that the mean temperature of the universe will drop as it expands and galaxies, stars, and planets move farther apart. But a team of international scientists has found that the average temperature of the cosmic gas spread across our universe has increased 10-fold over the past 10 billion years, reaching roughly 4 billion degrees Fahrenheit today, reports Universe Today. The researchers made use of data from the ESA's Planck Infrared Astronomical Satellite and the Sloan Digital Sky Survey to come up with the temperatures of distant cosmic gas as well as gas clouds that are closer to both Earth and the present time (read a detailed explanation of the science, which involved "redshift" measurements, here).
As for what's at work behind the increase, Ohio State University astrophysicist Yi-Kuan Chiang, the lead author of the study in the Astrophysical Journal, explains: "As the universe evolves, gravity pulls dark matter and gas in space together into galaxies and clusters of galaxies. The drag is violent—so violent that more and more gas is shocked and heated up." And it's a trend that "will continue and become more intense as the expansion of the Universe continues to accelerate," per Universe Today. This may come with consequences. As Popular Mechanics points out, a hotter universe will likely mean more cosmic radiation, which already poses a threat to astronauts and mechanical systems. (A science writer argues the Big Bang never happened.)