The fusion of two neutron stars set off the blast, which caused them to collapse and form a black hole.

Scientists call the explosion a kilonova, which occurs when two neutron stars merge together.

Researchers marvelled at the explosion.

"It is a perfect explosion in several ways," said astrophysicist Albert Sneppen of the Cosmic Dawn Center in Copenhagen, lead author of the research published in the journal Nature.

"It is beautiful, both aesthetically, in the simplicity of the shape, and in its physical significance."

Mr Sneppen said the colours which emit off of the kilonova take the shape and image of the 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," Mr Sneppen added.

Scientists were able to study the kilonova using the European Southern Observatory's Chile-based Very Large Telescope.

What is a kilonova?

To put it simply, this is when two neutron stars merge together and create a blast.

The neutron stars which had a combined mass of about 2.7 times that of the sun, orbited each other for billions of years before colliding at high speeds and exploding.

This unravelled in a galaxy called NGC 4993, which is about 140 to 150 million light years away from Earth - the distance light travels in a year.

Kilonova explosions were first proposed in 1974 and officially confirmed in 2013.

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However, what they looked like was unknown until the discovery of this one in 2017 which has since been extensively studied.

Scientists expected the explosion would look like a flattened disk.

"To be honest, we are really going back to the drawing board with this," Cosmic Dawn Center astrophysicist and study co-author Darach Watson said.

Mr Watson said there was "fundamental physics here that we don't understand yet", due to "densities greater than an atomic nucleus, temperatures of billions of degrees and magnetic fields strong enough to distort the shapes of atoms".

The life of a neutron star

The neutron stars first began as normal stars, these are called binary stars (a system of two stars that orbit around each other).

A neutron star is formed when a star runs out of fuel and collapses.

Leaving behind a small, dense core about 12 miles in diameter but carrying more mass than the sun.

After drawing closer and orbiting at a faster speed, the stars then stretch out before colliding, causing an explosion known as the kilonova.

Scientists said materials such as gold, platinum, arsenic, uranium and iodine were seen in space due to the intensity of the blast.

They offered some theories to explain the spherical shape of the explosion, including energy released from the short-lived single neutron star's enormous magnetic field or the role of enigmatic particles called neutrinos.

"This is fundamentally astonishing, and an exciting challenge for any theoreticians and numerical simulations," Mr Sneppen said.

"The game is on."