Astronomers Marvel at ‘Perfect Explosion,’ a Spherical Cosmic Fireball

A perfectly spherical explosion called a kilonova that followed the merger of two very defense objects called neutron stars—remnants of massive stars after supernova explosions that was observed 140-150 million light-years away from Earth is seen in this handout illustration obtained on Feb. 15, 2023. Albert Sneppen/Handout via Reuters

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.