Astronomers marvel at 'perfect explosion,' a spherical cosmic fireball
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 km).
The existence of kilonova explosions was proposed in 1974 and confirmed in 2013, but what they looked like was unknown until this one was detected in 2017 and studied intensively.
"It is a perfect explosion in several ways. It is beautiful, both aesthetically, in the simplicity of the shape, and in its physical significance," said astrophysicist Albert Sneppen of the Cosmic Dawn Center in Copenhagen, lead author of the research published in the journal Nature.
"Aesthetically, the colors the kilonova emits quite literally look like a sun - except, of course, being a few hundred million times larger in surface area. Physically, this spherical explosion contains the extraordinary physics at the heart of this merger," Sneppen added.
The researchers had expected the explosion to perhaps look like a flattened disk - a colossal luminous cosmic
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