Either way, you don’t want to end up near a neutron star.
These stellar beasts, composed mostly of neutrons, are essentially super-dense cosmic corpses wandering through space and, with incomprehensible gravitational fields, torturing everything in their path.
They are like the little brothers of black holes. When large stars (at least 20 times the size of our sun) die, they become black holes, but when smaller stars (between about eight and 20 times the size of our sun) die, they turn into neutron stars. A tablespoon of this terrifying orb would weigh more than the whole of Mount Everest. You get the point.
So here’s a thought: what would you expect if we took two vicious neutron stars and smashed them together?
Well I would say, nothing except what scientists have just observed.
According to a new study, published Wednesday in the journal Nature, astrophysicists analyzed data from a neutron star collision – a kilonova – detected in 2017 and found that the cosmic crash had formed a perfectly spherical explosion. It was unexpected.
“No one expected the explosion to look like this. It makes no sense for it to be spherical, like a ball. But our calculations clearly show that it is,” said Darach Watson, associate professor at the Niels Bohr Institute and co-author of the study. said in a press release.
Watson suggests that “this probably means that the kilonova theories and simulations that we have considered over the past 25 years lack important physics.”
Albert Sneppen, first author of the study and a doctoral student at the Niels Bohr Institute, suggests that a huge amount of energy may have blown out from the center of the explosion to create its oddly round shape.
The idea is that such energy output could have smoothed out the creases and other asymmetrical aspects of the object, presenting us with what basically looks like a circular cosmic balloon. “So the spherical shape tells us that there’s probably a lot of energy at the core of the collision, which was unexpected,” Sneppen said.
Sneppen also proposes that in the milliseconds in which the two neutron stars collided to form a giant neutron star, this newly created mega star could have emitted a bunch of neutrinos.
Besides being strange little phantom particles that fly through everything without leaving a trace – billions of them are going through your body right now, but you can’t tell because they are maze around your atoms – the neutrinos can have a special interaction with neutrons. They can convert heavy subatomic particles into protons and electrons. So maybe neutrons from neutron stars have been converted?
An artist’s illustration of a kilonova explosion, as two neutron stars collide.
Robin Dienel/Carnegie Institution for Science)
This concept is particularly interesting because it would explain how lighter elements could have formed with the kilonova as recorded by the team.
“This idea also has shortcomings, but we think neutrinos play an even bigger role than we thought,” Sneppen said.
In terms of the puzzling explosion shape, however, Watson explained another possible reason. Complex physics dictates what happens after two neutron stars collide – whether the collision creates a larger neutron star or collapses to form a black hole.
“Perhaps,” Sneppen postulated, “some kind of ‘magnetic bomb’ is created as energy from the hypermassive neutron star’s enormous magnetic field is released as the star collapses into a black hole. The release of magnetic energy could cause the material in the explosion to be distributed more spherically. In this case, the birth of the black hole can be very energetic.”
Time is the only cure for these puzzling cosmic mysteries.
Star-tographers
On an unrelated topic, however, the duo also point out that if all the kilonovas across the universe are actually that bright, shiny, and spherical, they may serve another purpose: stellar mapping.
To map the rate at which our universe is expanding exponentially — a major confound in itself — scientists need landmarks and guides, just as you would expect a mapmaker of Earth to do when it maps our rocky planet.
Measure how the distances between various cosmic objects increase over time and you can extrapolate how the universe is continually swelling outward. It is, in fact, somewhat like this that Edwin Hubble originally showed humanity in 1929 that our cosmic realm is expanding in the first place. He had used a huge telescope to record the galaxies moving further and further away from us, and from each other, faster over time.
But the point is that the measurement control points should be as uniform as possible to get the best mathematical results.
For example, a popular distance gauge for galactic measurements are stars known as RR Lyrae stars, because they pulsate the light they emit, so it is possible to get average brightness on them. Otherwise, if you look at a standard star to measure the structure of our galaxy, you might not know if it is very far away or if it is really faint for some reason.
In fact, a team of astronomers announced that they had followed RR Lyraes around the Milky Way until they managed to find the edge of our home galaxy.
When it comes to shape, however, neutron star collisions seem to be the key.
“If they’re bright and mostly spherical, and if we know how far away they are, we can use kilonovae as a new way to measure distance independently — a new kind of cosmic ruler,” Watson said. “Knowing what the shape is is crucial here, because if you have an object that’s not spherical, it emits differently, depending on your viewing angle. A spherical explosion [provides] much more precision in the measurement.”
