Third Black-Hole Merger Proves (Yet Again) That Einstein Was Right

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It may have happened some 3 billion light-years away, but we’re still feeling the aftershocks of the latest cosmic clash. Scientists announced this week that the Laser Interferometer Gravitational-Wave Observatory (LIGO) has again detected gravitational waves, or ripples in space and time, caused by the collision of two black holes in outer space. This extraterrestrial merger formed an enormous pit of darkness, with some 49 times the mass of the sun.

According to data picked up by the Laser Interferometer Gravitational-Wave Observatory (LIGO), the two black holes that smashed together some 3 billion light-years from here were large in themselves, measuring 19 and 32 times the mass of the sun. But when they merged, they created a monster.

Such a dramatic merger may seem alarming, but it appears we should start getting used to it. This is the third black-hole collision scientists have reported in less than two years, suggesting such events might occur quite frequently in the distant reaches of space.

During a news conference yesterday announcing the detection of gravitational waves from the latest collision (which occurred back on January 4), LIGO’s team of scientists said collisions between massive black holes are so common that they expect to start detecting as many as one per day once the observatory begins operating at its full capacity.

LIGO’s observations come from two detectors—located in Hanford, Washington, and Livingston, Louisiana—and are analyzed by an international collaboration of more than 1,000 scientists. Though the observatory began operating in 2002, it wasn’t sensitive enough to detect much of anything until it underwent a major upgrade, known as Advanced LIGO, which was completed in late 2014.

In September 2015, during a test run several days before the official search began, Advanced LIGO detected gravitational waves for the first time in history. These ripples in the fabric of space and time, caused by a black-hole collision some 1.3 light years from Earth, provided the first concrete evidence of a phenomenon first proposed by Albert Einstein in 1916 in his theory of general relativity.

By the time scientists announced that mind-blowing discovery in February 2016, LIGO had already picked up waves from a second black-hole collision in late 2015—on Christmas Day, no less. The third black-hole merger, announced this week, occurred much further away than the previous two. The gravitational waves it caused had to travel some 3 billion light-years to get here, compared with 1.3 and 1.4 billion light-years, respectively, for the first two. In addition, the latest merger revealed some new, intriguing clues about how the two black holes were moving in relation to each other, and even how they may have formed in the first place.

Pairs of black holes not only spiral around each other; they also spin individually on their own axes, just like the Earth and most other planets do. A statement from LIGO about the new discovery, Whitney Clavin of the California Institute of Technology (Caltech) describes this dynamic as “like a pair of ice skaters spinning individually while also circling around each other.”

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