Scientists find ‘perfect’ explosion in space that ‘makes no sense’

Scientists have spotted a “perfect” explosion in space that they say “makes no sense”.

For years, researchers have been trying to understand the nature of “kilonovae”, the huge explosions that happen when two neutron stars smash into each other. They are among the most powerful explosions in the universe, create the most extreme physical conditions in the cosmos, and in so doing are responsible for everything from black holes to gold.

But much about kilonovae still remains mysterious to scientists. That has included what shape the explosions themselves might be.

Researchers had presumed they were flattened and asymmetrical. That fit both with expectations and models of such explosions.

Now new research claims to have shown that the explosion is in fact a nearly perfect sphere, and is completely symmetrical. Researchers do not know how that is possible and suggest that it must be the result of unknown physics.

“No one expected the explosion to look like this. It makes no sense that it is spherical, like a ball. But our calculations clearly show that it is. This probably means that the theories and simulations of kilonovae that we have been considering over the past 25 years lack important physics,” said Darach Watson, associate professor at the Niels Bohr Institute and second author on the study.

The nature of those new physics is still unclear. Scientists have pursued a number of possible explanations – such as the idea that the explosion could include a sort of “magnetic bomb” at its centre that blows everything out from the inside – but some of them contradict other models and no satisfactory explanation has been found.

The unexpected shape might also help with other work, as well, including solving the long-running mystery of how quickly the universe is expanding. That speed is one of the most fundamental measurements in physics – but the various measurements are inconsistent, which has created yet another mystery.

“Among astrophysicists there is a great deal of discussion about how fast the Universe is expanding. The speed tells us, among other things, how old the Universe is. And the two methods that exist to measure it disagree by about a billion years. Here we may have a third method that can complement and be tested against the other measurements,” said Albert Sneppen, a student at the University of Copenhagen who is first author on a paper describing the findings.

At the moment, researchers use a variety of objects in space to measure that speed, calculating the distance between those objects and how it has changed. Kilonovae might be another useful addition to that set of objects, providing another measurement.

“If they are bright and mostly spherical, and if we know how far away they are, we can use kilonovae as a new way to measure the distance independently – a new kind of cosmic ruler,” said Professor Watson.

“Knowing what the shape is, is crucial here, because if you have an object that is not spherical, it emits differently, depending on your sight angle. A spherical explosion provide much greater precision in the measurement.”

The new findings are taken from data first taken in 2017, on a kilonova 140 million light-years away, which was the first to be examined in detail. That data is still providing fresh insights such as this one to the scientists who continue to try and understand it.

In the years to come, however, scientists hope to gather information on more kilonovae, including from the LIGO observatories that are detecting ripples in the fabric of spacetime. With information on more explosions, researchers should be able to learn more about them, including how they get their unexpected and inexplicable shape.

The findings are reported in a new paper, ‘Spherical symmetry in the kilonova AT2017gfo/GW170817’, published in Nature.