Astronomers have heard the faint hum of gravitational waves echoing throughout the universe for the first time.
For nearly a decade, scientists have been hunting for the gravitational wave background, a faint but persistent echo of gravitational waves thought to have been set off by events that took place soon after the Big Bang and the mergers of supermassive black holes throughout the cosmos. While such a background was long theorized by physicists and sought by astronomers, signals of gravitational waves that make up that background have been hard to detect due to being faint, in addition to vibrating at decade-long timescales. Now, long-term observations have finally confirmed their presence.
In a highly anticipated and globally coordinated announcement on Wednesday (June 28), teams of scientists worldwide have reported the discovery of the "low pitch hum" of these cosmic ripples flowing through the Milky Way.
While astronomers don't definitively know what's causing the hum, the detected signal is "compelling evidence" and consistent with theoretical expectations of gravitational waves emerging from copious pairs of "the most massive black holes in the entire universe" weighing as much as billions of suns, said Stephen Taylor, a gravitational wave astrophysicist at Vanderbilt University in Tennessee who co-led the research.
Hints of the same signal were announced in a series of papers published by scientists in China, India, Europe and Australia. They say the signals may be coming from merging supermassive black holes that are caught in cosmic dances, circling each other in orbits that shrink across millions of years. During this process, they release energy in the form of gravitational waves that reverberate throughout the universe  —  waves astronomers now say they have detected.
Scientists report that the observed background hum of gravitational waves has grown in significance over time, providing tantalizing proof that there may be hundreds of thousands or even millions of supermassive black holes about to merge in the next few hundred thousand years, even though the gargantuan objects themselves haven't yet been spotted.
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