Astrophysical Jets in Relativistic Regime : Thermal and Radiative Driving

TL;DR

This paper investigates how radiation, especially in a relativistic context, influences jet acceleration around black holes, highlighting the significance of general relativity and internal shocks in jet dynamics.

Contribution

It provides a comprehensive relativistic analysis of radiation-driven jets, revealing the impact of strong gravity, jet composition, and other parameters on jet acceleration and internal shock formation.

Findings

Relativistic jets with electron-positron composition reach Lorentz factors up to 10.

Jets around AGNs are faster than those around microquasars.

Radiation can accelerate jets effectively even without thermal driving.

Abstract

We study the efficiency of radiation in driving jets around black holes. Including general relativity for the radiation driving, we also show that the radiation field is affected by strong gravitational field in non linear manner, making general relativistic analysis more significant. We obtained internal shocks in jets close to the base, as a result of non-conical cross section and nature of radiation field on jet dynamics. Theoretical evidence of internal shocks is significant, as these are required to explain high energy tail of the spectra of radio sources. Under thermal and radiative driving, jets with electron-positron composition are obtained to be achieving relativistic speeds up to Lorentz factors $\gamma \sim 10$ while for electron-proton composition it is $\gamma \sim 2$ for luminous discs. We also showed that extragalactic jets around AGNs are faster than those around microquasars. We obtain that through Compton scattering, relativistic jets generated with non relativistic temperatures, are efficiently heated by temperatures up to $T \sim 10^{11-12} \rm K$. Further, we obtained transonic solutions with relativistic terminal speeds, for bound state of the jet at the base (that is, generalized Bernoulli parameter $E < 1$), where gravity is dominant over thermal driving. In Thomson scattering regime no transonic solutions could be obtained. This shows that radiation, in fact, has greater role as it not only accelerates the unbound matter of the jets, but the acceleration is effective even in absence of any other accelerating agent such as thermal acceleration. A detailed analysis of dependence of jet variables upon various parameters like plasma composition, magnetic pressure in the disc, luminosity, accretion rate, jet geometry and jet launching energy etc, is carried out.