When it comes to “destroying” cosmic ghosts, only the most extreme objects in the universe may be up to the task: neutron stars.
Scientists have run simulations of collisions between these ultra-dense and dead stars, showing that such powerful events may be able to briefly “trap” neutrinos, otherwise known as “ghost particles.” The discovery could help scientists better understand neutron star mergers as a whole, which are events that create environments turbulent enough to forge elements heavier than iron. Such elements cannot even be created in the hearts of the stars – and that 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 extremely small mass. These characteristics mean that they very rarely interact with matter. To put that into perspective, as you read this sentence, more than 100 trillion neutrinos are streaming through your body at near the speed of light, and you can’t feel a thing.
These new simulations of merging neutron stars were conducted by Penn State University physicists, and ultimately showed that the point where these dead stars meet (the interface) becomes incredibly hot and dense. In fact, it gets extreme enough to trap a bunch of those “cosmic ghosts.”
At least for a short time, anyway.
Despite their lack of interaction with matter, the neutrinos created in the collision would be trapped at that neutron-star-merger interface and become much hotter than the relatively cool hearts of colliding dead stars.
Connected: James Webb Space Telescope discovers neutron star mergers create gold in space: ‘It was exciting’
This is referred to as neutrinos being “out of thermal equilibrium” with the cores of cool neutron stars. During this hot phase, which lasts about two to three milliseconds, the team’s simulations showed that neutrinos can interact with the neutron star’s melting matter, helping to restore thermal equilibrium.
“Pre-merger neutron stars are effectively cold. While 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, an assistant professor of physics, astronomy. and astrophysics at Penn State’s Eberly College of Science, a statement said. “As they collide, they can get really hot. The interface of colliding stars can heat up to temperatures in the trillions of degrees Kelvin. However, they are so dense that photons cannot escape to dissipate the heat; instead , we think they cool by emitting neutrinos.”
Setting cosmic ghost traps
Neutron stars are born when a massive star 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 inward thrust of its own gravity.
This initiates a series of nuclear collapses that cause the fusion of heavier elements, which then produce even heavier the elements. This chain ends when the dying star’s heart is filled with iron, the heaviest element that can be forged in the core of even more massive stars. Then, gravitational collapse occurs again, causing 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 the interior of neutron stars. Negative electrons and positive protons are forced together, creating 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 – until the birth of black holes.
The result of this series of collapses is a dead dense star, or neutron star, with one to two times the mass of the original star – compressed into a width of about 12 miles (20 kilometers). For context, the matter that makes up 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 send out ripples in the fabric of space and time called gravitational waves.
As these gravitational waves echo 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 be pulled together. The closer they orbit, the faster they emit gravitational waves—and the faster their orbits tighten further. Eventually, the neutron star’s gravity takes over and the dead stars collide and merge.
This collision creates a “spray” of neutrons, enriching the environment around the fusion 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 create 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 as neutrons split apart, the team says, creating electrons and protons. And the researchers wanted to know what might happen during these initial moments. To gather some answers, they created simulations that use a large amount of computing power to model binary neutron star mergers and the physics associated with such events.
The Penn State team’s simulations revealed for the first time that, for a brief moment, the heat and density created by a neutron star collision is enough to trap even neutrinos, which in all other circumstances would have earned their ghost nicknames. .
“These extreme events stretch the limits of our understanding of physics, and studying them allows us to learn new things,” added Radice. “The period when the merging stars are out of equilibrium is only two to three milliseconds, but like temperature, time is relative here; the orbital period of the two stars before the merger can be as little as a millisecond.
“This brief out-of-equilibrium phase is when the most interesting physics happens. 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 can affect the light signals from these powerful events that can be observed on Earth.
“How neutrinos interact with stellar matter and how they are ultimately emitted can affect the oscillations of the two stars’ merged remnants, which in turn can affect what the merger’s electromagnetic and gravitational wave signals look like when they reach the us here on Earth,” team member Pedro Luis Espino, a postdoctoral researcher at Penn State and the University of California, Berkeley, said in the statement. “Next-generation gravitational wave detectors can be designed to look for these kinds of signal differences. In this way, these simulations play a crucial role, allowing us to gain 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 a laboratory to study them experimentally, so the best window we have into understanding what happens during a binary neutron star merger is through simulations of based on mathematics arising from Einstein’s theory of general relativity.”
The team’s research was published May 20 in the journal Physical Reviews Letters.
#Neutron #star #collisions #briefly #block #swarm #cosmic #ghosts
Image Source : www.space.com