Young researchers from ITMO University have described how intense directed radio emission is produced by neutron stars. Based on the transitions of particles between gravitational states, that is, quantum states in the gravitational field, they have developed a model. They were the first to explain these states for electrons found on the surface of neutron stars.
The physical parameters acquired with the help of the developed model are in accordance with real-time experimental results. The outcomes of the study have been reported in The Astrophysical Journal.
Neutron stars are among the most incredible celestial objects because their density is next only to black holes. There exist no individual nuclei and atoms inside the neutron stars. Furthermore, such a high density results in the tremendous gravity of the neutron stars, in turn leading to distinctive physical properties, such as directed radio emission, which had a vital role in the discovery of neutron stars.
It was in 1967 that the radiation from neutron stars was first observed on Earth in the form of periodic signals, at first leading researchers to propose that it might be from an extraterrestrial civilization. Yet, they quickly understood that the radiation of neutron stars had a natural origin and did not include any unique information. The strict periodicity was found to be the outcome of an unconventional propagation path. Radio waves emitted by neutron stars are in the form of a narrow beam “shining” through space similar to a beacon during the rotation of the star. Hence, it is observed that the radio emission of neutron stars is in the form of periodic pulsations.
One of the most mysterious questions related to the physical aspects of neutron stars is the mechanism responsible for the generation of such a directed radio emission. In the last five decades, researchers have not been able to find a clear solution to this puzzle. In the recent past, a group of theoretical physicists from ITMO University explained how radio emission is generated by pulsars. A theoretical model was developed by the physicists based on the analogous states noticed in electrons in semiconductor nanocrystals as well as those in gravitational fields.
Researchers investigated the movement of electrons at the surface of a neutron star. It is hard for the electrons to pass through the surface owing to the high density of matter within the star. At the same time, electrons get attracted to the surface of the star due to strong gravity. Consequently, particles get “trapped” inside a thin layer just above the star’s surface. As specified by the laws of quantum mechanics, only discrete values can be taken by the energy of the trapped electrons. When the electrons fall onto the neutron star’s surface, they go through the discrete gravity states, thus emitting energy in the form of radio wave beams.
Environment on the surface of a neutron star is very similar to the one that exists within a laser. There exists the so-called population inversion, meaning that the environment is rich with high-energy particles. As they move to the lower energy levels, they emit radiation that causes nearby particles to reduce their energy as well. We evaluated the frequency of electron transitions between gravitational conditions on a neutron star and saw that they correspond to the radio band. We never even suspected that this was something no one had done before, but it turned out that we were, indeed, the first.
Nikita Teplyakov, Researcher at the Laboratory of Modeling and Design of Nanostructures at ITMO University
The physicists stated that this research started in a quantum mechanics class when they worked on a task. “The task was pretty trivial: we had to describe the gravitational state on the surface of Earth. But on Earth, gravity is not very strong, so no interesting effects emerge; it is almost impossible to observe gravity conditions here. Therefore our professor Yuri Rozhdestvensky suggested we do the same task for a neutron star with a strong gravity. When we realized that we stumbled upon something interesting, we began developing a model. It turned out that we obtained a quite accurate description of the experimental data,” stated Tatiana Vovk, a member of the Laboratory of Modeling and Design of Nanostructures.
The researchers remark that in spite of its revelations, this study used well-known and simple principles of physics. Specifically, the radio emission amplification mechanism for neutron stars is analogous to one of the traditional lasers. Moving forward, the researchers aim to employ their model for investigating the gravitational states of other colossal objects in the Universe.