Scientists Reveal Influence of Plasma Composition on Astrophysical Jet Dynamics

Astrophysical jets, which are beams of ionized matter emitted from celestial objects like black holes and neutron stars, have long puzzled researchers regarding their exact composition.

Scientists from Aryabhatta Research Institute of Observational Sciences (ARIES) have investigated the plasma composition of astrophysical jets, revealing its impact on their propagation velocities and internal structures. Astrophysical jets, which are beams of ionized matter emitted from celestial objects like black holes and neutron stars, have long puzzled researchers regarding their exact composition.

Despite extensive research, it remains uncertain whether these jets consist of electrons, protons, or positrons (positively charged electrons). Understanding the jet composition is crucial to identifying the physical processes occurring near black holes and neutron stars. Typically, theoretical studies of jet thermodynamic properties—such as mass density, energy density, and pressure—lack information on the plasma composition. This relationship, known as the equation of state of jet matter, is essential for accurate modeling.

The study, led by Raj Kishor Joshi and Dr. Indranil Chattopadhyay from ARIES, utilized a relativistic equation of state, partly proposed by the researchers in a previous paper, to examine the dynamics of jets composed of various plasma mixtures. Their research, published in the Astrophysical Journal (ApJ), upgraded a numerical simulation code developed by Dr. Chattopadhyay to include the new equation of state, enabling the analysis of jets containing electrons, positrons, and protons.

The findings demonstrated that plasma composition significantly affects jet propagation speeds, with electron-positron jets traveling slower than jets containing protons, despite initial expectations. This is intriguing given that protons are about two thousand times more massive than electrons or positrons. The study highlighted that variations in plasma composition alter the internal energy of jets, thereby influencing their propagation speeds and internal structures, such as the number and strength of recollimation shocks and the dynamics of reverse shocks.

Electron-positron jets were observed to exhibit more pronounced turbulent structures, which contribute to their deceleration. These turbulent structures can impact the stability of the jets, suggesting that plasma composition may also play a role in their long-term stability.

Key Findings:

Plasma composition affects jet propagation speeds: Electron-positron jets are slower than proton-containing jets.

Changes in plasma composition alter internal jet energy, affecting propagation speeds and internal structures.

Electron-positron jets show more pronounced turbulent structures, influencing jet stability.