A kiloparsec-scale internal shock collision in the jet of a nearby radio galaxy

• Published in: Nature (London) 2015-05, Vol.521 (7553), p.495-497
• Main Authors: Meyer, Eileen T., Georganopoulos, Markos, Sparks, William B., Perlman, Eric, van der Marel, Roeland P., Anderson, Jay, Sohn, Sangmo Tony, Biretta, John, Norman, Colin, Chiaberge, Marco
• Format: Article
• Language: English
• Subjects: 639/33/34/863; 639/33/34/864; Active galaxies; Analysis; Astrophysics; Collisions (Physics); Humanities and Social Sciences; Jets; letter; Magnetic fields; multidisciplinary; Science; Space telescopes; Stars & galaxies
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature14481

Observations of a collision between two knots in the jet of nearby radio galaxy 3C 264 support the internal shock model of how the jet plasma is energized. Tangling knots drive jet from super-massive black hole Using a twenty-year dataset of Hubble Space Telescope images, Eileen Meyer et al . have tracked the motion of high-energy plasma in a jet produced by a super-massive black hole in a nearby radio galaxy. The authors find that one bright 'knot' of plasma in the jet has been catching up with a slower-moving knot just downstream. Images taken in 2014 record the first stages of their inevitable collision. Colliding knots have long been theorized as capable of accelerating the particles that produce high-energy radiation in many astrophysical jets, a mechanism known as the 'internal shock model', but this is the first time such a collision has been observed. Jets of highly energized plasma with relativistic velocities are associated with black holes ranging in mass from a few times that of the Sun to the billion-solar-mass black holes at the centres of galaxies 1 . A popular but unconfirmed hypothesis to explain how the plasma is energized is the ‘internal shock model’, in which the relativistic flow is unsteady 2 . Faster components in the jet catch up to and collide with slower ones, leading to internal shocks that accelerate particles and generate magnetic fields 3 . This mechanism can explain the variable, high-energy emission from a diverse set of objects 4 , 5 , 6 , 7 , with the best indirect evidence being the unseen fast relativistic flow inferred to energize slower components in X-ray binary jets 8 , 9 . Mapping of the kinematic profiles in resolved jets has revealed precessing and helical patterns in X-ray binaries 10 , 11 , apparent superluminal motions 12 , 13 , and the ejection of knots (bright components) from standing shocks in the jets of active galaxies 14 , 15 . Observations revealing the structure and evolution of an internal shock in action have, however, remained elusive, hindering measurement of the physical parameters and ultimate efficiency of the mechanism. Here we report observations of a collision between two knots in the jet of nearby radio galaxy 3C 264. A bright knot with an apparent speed of (7.0 ± 0.8) c , where c is the speed of light in a vacuum, is in the incipient stages of a collision with a slower-moving knot of speed (1.8 ± 0.5) c just downstream, resulting in brightening of both knots—as seen in the most recent epoc