In the realm of astrophysics, a trio of researchers from the University of Chinese Academy of Sciences—Zong-kai Peng, He Gao, and Xian-Fei Zhang—have been delving into the cosmic dance of neutron stars and white dwarfs. Their recent study, published in the Monthly Notices of the Royal Astronomical Society, explores the dramatic consequences of a head-on collision between these two stellar remnants.
Neutron stars and white dwarfs are the dense, compact cores left behind after stars have exhausted their nuclear fuel. Neutron stars are incredibly dense, with a teaspoon of neutron star material weighing as much as a mountain on Earth. White dwarfs, while also dense, are less so, with a composition that can vary depending on the original star’s mass. The researchers focused on three types of white dwarfs: helium, carbon-oxygen, and oxygen-neon.
The team’s simulations revealed that the outcomes of such collisions depend heavily on the mass and type of the white dwarf. In some cases, the collision can trigger a thermonuclear explosion. For this to happen, two conditions must be met: the collision must heat the white dwarf to a high enough temperature to ignite nuclear reactions, and the burning material must remain in a degenerate state, a condition where pressure does not increase with temperature. If these conditions are satisfied, the collision can lead to a sub-Chandrasekhar Type Ia supernova, a type of explosion that is important for understanding the evolution of the universe.
However, not all collisions result in such dramatic explosions. In some cases, the neutron star can become bound within the white dwarf, forming a Thorne-Zytkow-like object (TZlO). This can happen if the white dwarf material exerts enough drag on the neutron star to prevent its escape, without triggering a thermonuclear explosion. The researchers found that this scenario is possible with low-mass carbon-oxygen and oxygen-neon white dwarfs, provided that the viscous coefficient—the measure of the material’s resistance to the neutron star’s motion—is sufficiently large.
While this research may seem far removed from the energy industry, understanding these cosmic events can have practical applications. For instance, Type Ia supernovae are used as standard candles to measure cosmic distances, helping us understand the expansion of the universe and the nature of dark energy. Moreover, the study of these extreme environments can provide insights into nuclear reactions and the behavior of matter under extreme conditions, which can have implications for energy production and other technologies.
This article is based on research available at arXiv.