The four previous times LIGO scientists detected gravitational waves they belonged to the merger of black holes, which are the only objects in the universe denser than neutron stars. LIGO scientists were expecting to see neutron stars merge, and were ready to differentiate it from other events that can produce gravitational waves, such as supernovae (exploding stars). The timing of this major announcement is serendipitous: The scientists who built LIGO just won this year’s Nobel Prize in Physics.

The serendipity of a neighborhood event

The LIGO scientists observed these waves for about 100 seconds—before the moment the two neutron stars crashed into each other. Two seconds after that, gamma rays from the stellar merger reached the Earth. Over the next days and weeks, the event was recorded by 70 ground- and space-based observatories that LIGO had alerted. That’s special, because blackhole mergers don’t release visible light. That’s why this data from a merger of a neutron star would provide LIGO scientists information they had never seen before.

“On the cosmological scale, this happened in our neighborhood,” says Andreas Freise of the University of Birmingham and a LIGO collaborator. It’s good luck, then, also on a cosmological scale that humans happen to have invested in building the right instruments to watch such an event at just about the right time. (The instrument had been expecting such a neutron-star merger, but researchers had thought it would likely have occurred much farther away.)

In the days to follow, other types of electromagnetic radiation—including X-ray, ultraviolet, optical, infrared, and radio waves—were detected. Each element has a unique electromagnetic signature. Scientists were able to detect signatures related to an occurrence called the “r process” which was thought to create heavy elements. It’s here that elements like gold, platinum, and uranium are made.

“This detection has genuinely opened the doors to a new way of doing astrophysics,” Laura Cadonati, professor of physics at Georgia Tech and LIGO collaborator, said in a statement. “I expect it will be remembered as one of the most studied astrophysical events in history.” And now you, too, know where in the universe all the elements of the periodic table get made.

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