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[00:00.93] Space scientists say they have identified what might be the "perfect explosion," but much work remains to fully explain the observation.

[00:11.83] The explosion, called a kilonova, was observed in 2017 and has been studied carefully since then.

[00:22.71] Astronomers say a kilonova happens when two neutron stars crash into each other.

[00:28.83] The rapidly growing explosion that they described went beyond the researchers’ expectations.

[00:36.53] The event led to the formation of a black hole: an object with so much gravity that even light cannot escape it.

[00:45.83] The two neutron stars had a combined mass of 2.7 times that of our sun.

[00:53.53] They orbited each other for billions of years before crashing into each other at a high speed and exploding.

[01:02.56] This event took place in a galaxy called NGC 4993.

[01:09.20] The galaxy is at least 140 million light years away from Earth in the direction of the constellation Hydra.

[01:19.03] A light year is the distance light travels in a year.

[01:23.27] Astronomers used the European Southern Observatory's Chile-based Very Large Telescope to study the kilonova.

[01:32.84] The existence of kilonova explosions was proposed in 1974.

[01:39.21] The theory was confirmed in 2013.

[01:43.46] But astronomers did not know what they looked like until one was identified in 2017 and studied carefully.

[01:53.03] "It is a perfect explosion in several ways.

[01:57.27] It is beautiful...in the simplicity of the shape, and in its physical" importance, said Albert Sneppen of the Cosmic Dawn Center in Copenhagen, Denmark.

[02:08.96] Sneppen was the lead writer of the research published in Nature.

[02:13.75] The researchers had expected the explosion to look flat and round, with a jet of material coming out of it.

[02:22.51] "To be honest, we are really going back to the drawing board with this," said study co-writer Darach Watson of the Cosmic Dawn Center.

[02:32.87] "Given the extreme nature of the physical conditions...there may well be fundamental physics here that we don't understand yet," Watson added.

[02:43.50] The two neutron stars began their lives as large normal stars in a two-star system called a binary system.

[02:53.06] Each exploded and collapsed after running out of fuel, leaving behind a small and dense center, or core, only 20 kilometers across.

[03:04.48] The neutron stars then slowly drew nearer to each other.

[03:09.26] They were then stretched out and pulled apart because of the power of the other's gravity.

[03:15.90] Their inner parts crashed into each other at about 25 percent of the speed of light, creating the most intense magnetic fields in the universe.

[03:27.59] The explosion released the luminosity of a billion suns for a few days.

[03:33.70] The two briefly formed a single massive neutron star that then collapsed to form a black hole.

[03:42.20] The outer parts of the neutron stars, however, were stretched into long streamers, with some material flying off into space.

[03:52.29] During the process, the densities and temperatures were so strong that they created heavy elements, including gold, platinum, arsenic, uranium and iodine.

[04:06.63] Sneppen used the term challenge, meaning a difficult task or problem, to talk about the findings, which are hard understand.

[04:16.73] "This is fundamentally astonishing, and an exciting challenge for any theoreticians and numerical simulations," Sneppen said. "The game is on."