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No matter what, you won’t find yourself anywhere near a neutron star.
These star beasts, made mostly of neutrons, are basically ultra-dense cosmic corpses that roam space and, with unfathomably strong gravitational fields, torture everything in their path.
They are like the baby 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 become neutron stars. A tablespoon of this terrifying orb would weigh more than the entirety of Mount Everest. You get the point.
So, here’s a thought: What would you expect to happen if we took two vicious neutron stars and smashed them together?
Well, I would argue, everything except what the scientists have just observed.
According to a new study, published Wednesday in the journal Nature, astrophysicists analyzed data on a neutron star collision – a kilonova – discovered in 2017 and found that the cosmic crash formed a perfectly spherical explosion. It was unexpected.
“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,” Darach Watson, associate professor at the Niels Bohr Institute and study co-author, said in a statement.
Watson suggests, “this likely means that the theories and simulations of kilonova that we have considered over the last 25 years are missing important physics.”
Albert Sneppen, first author of the study and a doctoral student at the Niels Bohr Institute, suggests that perhaps a huge amount of energy was blown out from the center of the explosion to create its strange round shape.
The idea is that such an outflow of energy may have smoothed out any kinks and other asymmetric aspects of the object, presenting us with what initially looks like a circular cosmic balloon. “So the spherical shape tells us that there is probably a lot of energy at the core of the collision, which was unexpected,” Sneppen said.
Sneppen also offers that during the milliseconds when the two neutron stars collided to form a giant neutron star, the newly minted megastar may have emitted a flurry of neutrinos.
Beyond being weird little ghost particles that fly through everything without a trace—trillions of them are zipping through your body right now, but you can’t tell because they’re labyrinthine around your atoms—neutrinos can have a special interaction with neutrons. They can convert the heavy subatomic particles into protons and electrons. So, maybe the neutron stars’ neutrons were 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 the team recorded.
“This idea also has flaws, but we think that neutrinos play an even more important role than we thought,” Sneppen said.
As for the puzzling explosion shape, 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, “a kind of ‘magnetic bomb’ is created at the moment when the energy from the hypermassive neutron star’s enormous magnetic field is released when the star collapses into a black hole. The release of magnetic energy could cause the matter in the explosion to be distributed more spherically.” If so, the birth of the black hole could be very energetic.”
Time is the only remedy for such perplexing cosmic mysteries.
Star-tographs
On an unrelated matter, the duo also points out that if all kilonovae across the universe are indeed this bright, brilliant and spherical, they could serve another purpose: stellar cartography.
To chart the rate at which our universe is expanding—a huge conundrum in itself—scientists need landmarks and guides just as you’d expect an Earth cartographer to map our rocky planet.
Measure how distances between various cosmic objects increase over time, and you can extrapolate how the universe is constantly ballooning outwards. This is actually in a way that Edwin Hubble originally showed humanity in 1929 that our cosmic realm is expanding in the first place. He had used a massive telescope to record galaxies moving further and further away from us, and apart, faster as time passed.
But the point is that measurement checkpoints must be as uniform as possible for the best mathematical results.
For example, a popular rangefinder for galactic measurements are stars known as RR Lyrae stars, because they kind of pulsate the light they emit, so it’s possible to get an 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’s very far away or just very faint for whatever reason.
In fact, a team of astronomers announced that they tracked RR Lyraes in the Milky Way until they were able to find the edge of our home galaxy.
When it comes to form, however, collisions with neutron stars 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 critical here, because if you have an object that’s not spherical, it emits differently depending on your angle of view. A spherical explosion (provides) much greater precision in the measurement.”
