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130 million light years

At 22：00 on October 16th（Beijing time）， the The Laser Interferometer Gravitational-Wave Observatory （LIGO） and Virgo Scientific Collaboration announced yet another detection of gravitational waves. This is the 5th time that human beings have detected gravitational waves， and the first time to have observed gravitational wave electromagnetic counterparts， which will usher in a new era of gravitational wave astronomy.

This is also the first gravitational wave of the combination of neutron stars， which is very similar to the gravitational wave signal generated by the double black holes earlier， but it lasts longer. The gravitational wave si from NGC 4993 galaxies in the constellation of Hydra about 130 million light years from Earth. A hundred seconds before merging， they revolved around each other 12 laps per second with a distance of 400km， radiating gravitational waves outward. They move closer and closer until they finally collide， forming new objects and emitting electromagnetic radiation.endprint