WASHINGTON—Astronomers have observed what might be the “perfect explosion,” a colossal and utterly spherical blast triggered by the merger of two very dense stellar remnants called neutron stars shortly before the combined entity collapsed to form a black hole.
Researchers on Wednesday described for the first time the contours of the type of explosion, called a kilonova, that occurs when neutron stars merge. The rapidly expanding fireball of luminous matter they detailed defied their expectations.
The two neutron stars, with a combined mass about 2.7 times that of our sun, had orbited each other for billions of years before colliding at high speeds and exploding. This unfolded in a galaxy called NGC 4993, about 140–150 million light years away from Earth in the direction of the constellation Hydra. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion kilometers)….