Astronomers don’t understand why the merger of two neutron stars creates a perfect, spherical explosion

They are kilonovae and they can help to know the age of the universe and at what speed it is expanding.

Let’s look at the stars (which is always good to remember our cosmic smallness). Those who deal with them call kilonova the phenomenon in which two neutron stars merge from a binary system.

Kilonovae are one of the largest explosions that occur in the universe and create the most extreme physical conditions in the cosmos. Astronomers also call them macronovae or r-type supernova processes.

Before we continue, let’s clarify. A neutron star is the result of the death of a massive supergiant star (one that has already used up its fuel), which explodes as a supernova. And a binary system is the one formed by two astronomical objects that are so close to each other that they are linked by their gravitational force.

We talk about kilonovas because one of these explosions is news. Scientists have detected the merger of two neutron stars that has created a spherical cosmic explosion, a “perfect” explosion. But astronomers say it “doesn’t make sense,” at least according to what science knew so far.

Actually, astronomers don’t know much about kilonovae. With the data they have and with the laws of physics in hand, they have assumed, for example, that the shape of these huge explosions was flat and asymmetric. But now an investigation throws those assumptions to the ground.

A kilonova 140 million light years away
An article titled Spherical symmetry in the kilonova AT2017gfo/GW170817 and published in Nature claims to have shown that the explosion has nothing to do with the assumed models, but that it is almost perfectly spherical in shape and completely symmetrical.

This is the conclusion of an investigation signed by Albert Sneppen, a student at the University of Copenhagen and lead author of the article, and Darach Watson, associate professor at the Niels Bohr Institute in Denmark and second author of the study.

It was in 2017 when a kilonova was detected in detail for the first time. This is AT2017gfo, which is 140 million light-years away. Like many other astronomers, Sneppen and Watson have studied the data obtained in recent years.

“These are two super-compact stars that orbit each other 100 times per second before collapsing. Our intuition, and all previous models, say that the explosive cloud created by the collision must have a flattened and rather asymmetrical shape,” explains Sneppen. But not.

They are just as surprised as the rest of his colleagues: they don’t know how it is possible that the kilonova they have studied has such a perfect shape. And they are so stunned that they have already suggested that the phenomenon can only be explained as the result of unknown physics. Also, the spherical shape indicates, to your surprise, that there is a lot of energy in the nucleus of the collision.

“It doesn’t make sense that it’s spherical, like a ball. But our calculations clearly show that it is. It probably means that the kilonovae theories and simulations we’ve been considering for the past 25 years are missing important aspects of physics.” Watson acknowledges

Why is the shape of a kilonova important?
From our ignorance, it is worth asking: and why is the shape of this explosion important, no matter how immense it is? It turns out that kilonovae, among other objects in space, can be used by astronomers to measure how fast the universe is expanding, calculating the distance between these objects and how it has changed.