When it comes to “breaking” space ghosts, only the most extreme objects in the universe can accomplish this task: neutron stars.
Scientists have run simulations of collisions between these ultradense and dead stars, showing that such powerful events may be able to briefly ‘capture’ neutrinos, otherwise known as ‘ghost particles’. The discovery could help scientists better understand neutron star mergers as a whole, events that create an environment turbulent enough to form elements heavier than iron. Such elements cannot be created even in the hearts of the stars – and this includes gold on the finger and silver around the neck.
Neutrinos are considered the “ghosts” of the particle zoo due to their lack of charge and incredibly small mass. These properties mean that they very rarely interact with matter. To put it into perspective, as you read this sentence, more than 100 trillion neutrinos are passing through your body at close to the speed of light, and you feel nothing.
These new simulations of merging neutron stars were performed by Penn State University physicists and finally showed that the point where these dead stars meet (the interface) is incredibly hot and dense. In fact, it’s extreme enough to catch a lot of those “space ghosts”.
At least for a short time.
Despite the lack of interaction with matter, the neutrinos produced in the collision would become trapped at the neutron-star-merger interface and become much hotter than the relatively cool hearts of the colliding dead stars.
Related: Gravitational waves reveal first-of-its-kind merger of neutron star and mysterious object
These are referred to as neutrinos that are “out of thermal equilibrium” with the cores of cold neutron stars. During this hot phase, which lasts about two to three milliseconds, the team’s simulations showed that neutrinos can interact with the merging mass of the neutron star, which in turn helps restore thermal equilibrium.
“Pre-merger neutron stars are effectively cold. Although they can be billions of degrees, Kelvin, their incredible density means that this heat contributes very little to the energy of the system,” team leader David Radice, assistant professor of physics, astronomy. and astrophysics at Penn State’s Eberly College of Science, he said in a statement. “As they collide, they can get really hot. The interface of colliding stars can heat up to temperatures in the trillions of degrees Kelvin. But they’re so dense that photons can’t escape to dissipate the heat; instead, we think they cool down by emitting neutrinos.”
Setting traps for space spirits
Neutron stars are born when a massive star with at least eight times the mass of the Sun runs out of the fuel needed for nuclear fusion in its core. After the fuel supply ends, the star can no longer support itself against the internal pressure of its own gravity.
This starts a series of core collapses that trigger the fusion of heavier elements, which then accumulate even harder Elements. This chain ends when the heart of a dying star is filled with iron, the heaviest element that can be forged in the core of even the most massive stars. Gravitational collapse then occurs again, triggering a supernova explosion that blows away the star’s outer layers and most of its mass.
Instead of creating new elements, this final core collapse creates an entirely new state of matter unique to neutron star interiors. Negative electrons and positive protons are forced together to create an ultra-dense soup of neutrons, which are neutral particles. An aspect of quantum physics called “degeneracy pressure” prevents these neutron-rich cores from collapsing further, although this can be overcome by stars of sufficient mass to collapse completely – giving birth to black holes.
The result of this series of collapses is a dense dead star, or neutron star, with one to twice the mass of the original star – packed into a width of about 20 kilometers. For context, the matter that comprises neutron stars is so dense that if a tablespoon of it were brought to Earth, it would weigh about as much as Mount Everest. Maybe more.
However, these extreme stars do not always live (or die) in isolation. Some binary star systems contain two stars massive enough to give birth to neutron stars. As these binary neutron stars orbit each other, they emit ripples in the very fabric of space and time called gravitational waves.
As these gravitational waves bounce off neutron star binaries, they carry angular momentum with them. This results in a loss of orbital energy in the binary system and causes the neutron stars to pull together. The closer they orbit, the faster they emit gravitational waves – and the faster their orbits narrow further. Eventually, neutron star gravity takes over and the dead stars collide and merge.
This collision creates “sprays” of neutrons, enriching the environment around the merger with free versions of these particles. These can be “captured” by atoms of elements in this environment during a phenomenon called the “rapid capture process” (r-process). This creates super-heavy elements that undergo radioactive decay to form lighter elements that are still heavier than iron. Think gold, silver, platinum and uranium. The decay of these elements also creates a burst of light that astronomers call a “kilonova.”
The first moments of neutron star collisions
Neutrinos are also created during the first moments of a neutron star’s merger, when neutrons are torn apart, the team says, creating electrons and protons. And scientists wanted to know what might happen during those initial moments. To get some answers, they created simulations that use massive amounts of computing power to model binary neutron star mergers and the physics involved in such events.
The Penn State team’s simulations revealed for the first time that, for a brief moment, the heat and density generated by a colliding neutron star is enough to trap even neutrinos, which would otherwise have earned their ghostly nicknames.
“These extreme events push the boundaries of our understanding of physics, and studying them allows us to learn new things,” added Radice. “The period when merging stars are out of balance is only two to three milliseconds, but like temperature, time is relative; the orbital period of two stars before merging can be as little as one millisecond.
“This brief out-of-equilibrium phase is when the most interesting physics occurs. Once the system returns to equilibrium, the physics is better understood.”
The team thinks that the precise physical interactions that occur during neutron star mergers could influence the light signals from these powerful events that can be observed on Earth.
“How neutrinos interact with the stellar mass and are eventually emitted can affect the oscillations of the merged remnants of two stars, which in turn can affect what the merger’s electromagnetic and gravitational wave signals look like when they reach us. on Earth,” team member Pedro Luis Espino, a postdoctoral researcher at Penn State and the University of California, Berkeley, said in a statement. “Next-generation gravitational wave detectors could be designed to look for these kinds of differences in the signals. In this way, these simulations play a key role, giving us insight into these extreme events while informing future experiments and observations in a kind of feedback loop.
“There is no way to reproduce these events in the laboratory so that we can study them experimentally, so the best window we have into understanding what happens during binary neutron star mergers is through simulations based on the mathematics that comes from Einstein’s theory general relativity.”
The team’s research was published May 20 in the journal Physical Reviews Letters.
Originally published on Space.com.