Relativistic jet

Relativistic jet

Abstract

The structure of relativistic jets in AGN on sales of light days reveals how energy propagates through jets, a process that is fundamental to galaxy evolution. A deeper understanding of jet physics will clarify the differences between radio-loud and radio-quiet quasars that manifest themselves near the supermassive black hole. We can also use relativistic jets to identify supermassive binary black holes remaining from galaxy mergers, and use orbital motion to derive the masses of the black holes. The search for binary black holes in the nuclei of galaxies will yield important information on their overall lifetime and on the processes occurring in galaxies that affect black holes and quasars. High-precision astrometric measurements, made using the technique of optical interferometry on a space-based platform, such as SIM Lite, are the key to answering these questions.

Relativistic Jets

Introduction

According to current AGN models, a supermassive black hole, with mass scaling as 0.1 percent of its host galaxy's spheroidal bulge, is surrounded by an accretion disk and corona, and in some cases a pair of relativistic jets. Unifying schemes seek to relate a few underlying physical parameters (mass, accretion rate, spin, magnetic field, viewing geometry) to the diverse observed properties of AGN. Observationally, in radio-quiet quasars (which make up 90 percent of all known quasars), the optical emission has a continuum power law, emission lines, and a thermal Big Blue Bump. Radio-loud quasars have an additional nonthermal power-law continuum attributed to strong relativistic jets. Figure 1 shows the canonical quasar model.

Figure 1: The origin of optical emission from a quasar nucleus (shown schematically, with logarithmic scaling) on scales that are not resolved by nay imaging telescope.

Spin-up of the newly-merged black holes in major merger galaxies may provide the immediate trigger for acceleration of strong relativistic jets in radio-loud quasars and galaxies. On the scale of light days to light weeks, the jets are triggered, collimated and accelerated. The inference of accretion disk spin rates from Iron K-alpha lines has given new insight into the situation near the central supermassive black hole (e.g., Reynolds and Fabian 2008).

However, the angular resolution needed to directly measure motions in the inner tenth of a parsec in quasars is beyond the reach of current optical and near-infrared ground- and space- based telescopes (Hubble 100 mass, Keck and Very Large Telescope Interferometers ~10 mass). Table 1 lists some key objects and their characteristics. Direct measurement of motions and position differences on scales of tens to hundreds of Schwarzschild radii has previously been achieved only at radio wavelengths with VLBI. We need similar angular resolution at optical wavelengths.

Sample Targets

Redshift or Distance

Distance subtended by 10 µas, Light Days

Optical Magnitude Range, V

Black Hole Mass, M

Class

M87

17 Mpc

1.3

17 (nucleus)

3.2*109

Nearby AGN

3C273

0.158

32

13-Dec

1.7*107

Nearest Quasar

OJ287

0.306

52

14-17

2.0*109

Blazar, binary candidate

3C279

0.536

73

14-18

2.8*108

Blazar

3C454.3

0.859

84

13-17

1.5*109

Blazar

Reference from mass estimates: M87: Macchetto et al. 1997; 3C273, 3C454.3: compilation by Woo and Urry 2002; 0J287: Valtonen et al. 2008a.

Discussion

Relativistic flows play a fundamental role in highly energetic astrophysical scenarios, ranging from accretion flows in the vicinity of compact stars and black holes, over ...