Emily Chan
After stars collapse, they can leave behind small, dense, and cold remains called neutron stars. If two stars collapse near each other, their neutron stars can merge with one another and become extremely hot.
Now, new research suggests that these collisions can temporarily trap neutrinos, which are particles known as “cosmic ghosts” due to their lack of charge and tiny nature.
A research team led by physicists at Pennsylvania State University created simulations that show how the neutrinos can be captured for two to three milliseconds. During this time, the neutrinos can interact weakly with stellar matter, which helps direct the particles back to equilibrium.
“For the first time in 2017, we observed here on Earth signals of various kinds, including gravitational waves, from a binary neutron star merger,” Pedro Luis Espino, the lead author of the study and a postdoctoral researcher at Penn State and the University of California, said.
“This led to a huge surge of interest in binary neutron star astrophysics. There is no way to reproduce these events in a lab to study them experimentally, so the best window we have into understanding what happens during a binary neutron star merger is through simulations based on math that arises from Einstein’s theory of general relativity.”
To better understand what happens during the collisions, the team generated computer simulations that model the merger of neutron stars. The simulations revealed that neutrinos can be trapped by the density and heat of the merger.
Before the merger, neutron stars are incredibly cold. As they collide, they can become super hot, heating up to temperatures in the trillions of degrees Kelvin. They can still interact with the matter of stars while out of equilibrium.
They are so dense that photons are unable to escape to make the heat go away. It is believed that they cool down by emitting neutrinos.
Neutron star mergers can create elements that are lighter but still heavier than iron. When these collisions occur, neutrons are sprayed everywhere into the environment. The atoms of elements in the environment grab the particles, a phenomenon known as the rapid-capture process.
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