Astronomers have observed what might be called a “perfect explosion,” a giant spherical explosion triggered by the merger of two very dense stellar remnants known as neutron stars just before when the combined entity collapses to form a black hole.
Researchers on Wednesday described for the first time the contours of a type of explosion, known as 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 total mass about 2.7 times the mass of our sun, orbited each other for billions of years before colliding at high speed and exploding. This takes place in a galaxy called NGC 4993, about 140-150 million light-years away. 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 kilometers).
The existence of kilonova explosions was suggested in 1974 and confirmed in 2013, but what they looked like remained unknown until this explosion was discovered in 2017 and studied intensively. .
“It was a perfect explosion in so many ways. It’s beautiful, both aesthetically, in simplicity,” said astrophysicist Albert Sneppen of the Cosmic Dawn Center in Copenhagen, lead author of the study. of its physical form and meaning”. Nature magazine.
“Aesthetically, the color the kilonova emits looks like a sun – except, of course, several hundred million times larger in surface area. Physically, this spherical explosion contains extraordinary physics at the heart of this merger,” added Sneppen.
The researchers had expected the explosion might look like a flat saucer – a giant glowing cosmic cake, possibly with a jet of matter spewing out of it.
“Honestly, we’re really getting back to the drawing board with this,” said Darach Watson, astrophysicist and Cosmic Dawn Center study co-author.
“Given the extreme nature of the physical conditions – for example, much more extreme than a nuclear explosion, with a density greater than that of an atomic nucleus, a temperature of billions of degrees, and a magnetic field strong enough to deform the shape of the atom – it’s very possible that there’s fundamental physics here that we don’t understand yet,” added Watson.
Kilonova was studied using the Very Large of the European Southern Observatory based in Chile. telescope.
Two neutron stars begin their lives as high-mass ordinary stars in a two-star system known as a binary system. Each exploded and collapsed after running out of fuel, leaving behind a small, dense core about 12 miles (20 km) in diameter but more massive than the sun.
Gradually, they came closer to each other, orbiting each other at very fast speeds. Each stretched and split in the final seconds before merging due to the strength of the other’s gravitational field. Their interior parts collide at about 25% the speed of light, creating the strongest magnetic field in the universe. The explosion unleashed the luminosity of about a billion suns over several days.
The two quickly formed a single massive neutron star, which then collapsed to form a black hole, an even denser object with gravity so strong that even light cannot escape. Okay.
Meanwhile, the outer parts of neutron stars are stretched into long bands, with some of the matter thrown into space. During this process, the density and temperature were so high that heavy elements were created, including Yellowplatinum, arsenic, uranium and iodine.
The researchers have proposed several hypotheses to explain the spherical shape of the explosion, including the energy released from the massive magnetic field of the short-lived single neutron star or the role of particles. mystery called neutrinos.
“This is fundamentally startling and an exciting challenge for any number theorist and simulator,” says Sneppen. “The game begins.”
