Astronomers marvel at the “perfect explosion”: a fully spherical cosmic fireball

astronomers have observed what could be the “perfect explosion”a colossal and completely spherical outburst caused by the merger of two very dense stellar remnants called stars of neutrons, shortly before the combined entity collapsed to form a black hole.

Researchers on Wednesday described for the first time the outlines of the type of explosion, called a kilonova, that occurs when neutron stars merge. The rapidly expanding fireball of luminous matter defied their expectations.

The two neutron stars, with a combined mass about 2.7 times that of our Sun, orbited each other for billions of years before colliding at high speed and exploding.

The event took place in a galaxy called NGC 4993, some 140-150 million light-years from Earth in the direction of the Hydra constellation.

The existence of kilonova explosions was proposed in 1974 and confirmed in 2013, but what they were like was unknown until it was detected in 2017 and extensively studied.

“It’s a perfect explosion in several ways. It is beautiful, both aesthetically for the simplicity of the form and for its physical meaning”said astrophysicist Albert Sneppen of the Cosmic Dawn Center in Copenhagen, lead author of the research published in the journal Nature.

“Aesthetically, the colors emitted by the kilonova literally resemble the sun, except, of course, that they are a few hundred million times larger in area. Physically, this spherical explosion contains the extraordinary physics at the heart of this fusion.”added sneppen. .

The researchers expected the explosion to perhaps resemble a flattened disk, a colossal luminous cosmic pancake, possibly with a jet of material pouring out of it.

“To be honest, we’re really going back to the drawing board with this.”said Darach Watson, an astrophysicist at the Cosmic Dawn Center and a co-author of the study.

“Given the extreme nature of the conditions, much more extreme than a nuclear explosion, for example, with densities greater than an atomic nucleus, temperatures in the billions of degrees, and magnetic fields strong enough to distort the shapes of atoms, There may well be fundamental physics here that we don’t yet understand.”Watson added.

The kilonova was studied using the Very Large Telescope of the European Southern Observatory, located in Chile.

The two neutron stars began their lives as normal stars in a binary system. Each exploded and collapsed after running out of fuel, leaving behind a small, dense core about 20 kilometers across but more massive than the sun.

Very gradually, they came closer to each other, orbiting at a very fast pace. Each stretched and separated in the final seconds before the merger due to the power of the other’s gravitational field. Their internal parts collided at approximately 25% of the speed of light, creating the strongest magnetic fields in the universe.

The explosion unleashed the luminosity of about 1,000 million suns for a few days.

The two bodies briefly integrated a single massive neutron star that then collapsed to form a black hole, an object even denser and with such ferocious gravity that not even light can escape.

(With information from Reuters)