Superluminal motion

Bursts of energy moving out along the relativistic jets emitted from these objects can have a proper motion that appears greater than the speed of light.

All of these sources are thought to contain a black hole, responsible for the ejection of mass at high velocities.

When measuring the movement of distant objects across the sky, there is a large time delay between what has been observed and what has occurred, due to the large distance the light from the distant object has to travel to reach us.

Correspondingly, if the object is moving away from the Earth, the above calculation underestimates the actual speed.

However it is not strictly necessary for this to be the case, and superluminal motion can still be observed in objects with appreciable velocities not directed towards the Earth.

[3] Superluminal motion is most often observed in two opposing jets emanating from the core of a star or black hole.

An embarrassment is that the average projected size [on the sky] of the outer structure is no smaller than that of the normal radio-source population.

In 1993, Thomson et al. suggested that the (outer) jet of the quasar 3C 273 is nearly collinear to the Earth's line-of-sight.

[9] The same group of scientists later revised that finding and argue in favour of a superluminal bulk movement in which the jet is embedded.

[10] Suggestions of turbulence and/or "wide cones" in the inner parts of the jets have been put forward to try to counter such problems, and there seems to be some evidence for this.

He may see the rate of change of position as apparently representing motion faster than c when calculated, like the edge of a shadow across a curved surface.

A relativistic jet coming out of the center of an active galactic nucleus is moving along AB with a velocity v, and is observed from the point O.

The apparent superluminal motion in the faint nebula surrounding Nova Persei was first observed in 1901 by Charles Dillon Perrine.

Perrine’s photograph of November 7th and 8th, 1901, secured with the Crossley Reflector, led to the remarkable discovery that the masses of nebulosity were apparently in motion, with a speed perhaps several hundred times as great as hitherto observed.”[13] “Using the 36-in.

telescope (Crossley), he discovered the apparent superluminal motion of the expanding light bubble around Nova Persei (1901).

Perrine studied this phenomenon using photographic, spectroscopic, and polarization techniques.”[14] Superluminal motion was first observed in 1902 by Jacobus Kapteyn in the ejecta of the nova GK Persei, which had exploded in 1901.

[15] His discovery was published in the German journal Astronomische Nachrichten, and received little attention from English-speaking astronomers until many decades later.

The discovery was the result of a new technique called Very Long Baseline Interferometry, which allowed astronomers to set limits to the angular size of components and to determine positions to better than milli-arcseconds, and in particular to determine the change in positions on the sky, called proper motions, in a timespan of typically years.

The apparent velocity is obtained by multiplying the observed proper motion by the distance, which could be up to 6 times the speed of light.

In the introduction to a workshop on superluminal radio sources, Pearson and Zensus reported The first indications of changes in the structure of some sources were obtained by an American-Australian team in a series of transpacific VLBI observations between 1968 and 1970 (Gubbay et al.

[19] Following the early experiments, they had realised the potential of the NASA tracking antennas for VLBI measurements and set up an interferometer operating between California and Australia.

The change in the source visibility that they measured for 3C 279, combined with changes in total flux density, indicated that a component first seen in 1969 had reached a diameter of about 1 milliarcsecond, implying expansion at an apparent velocity of at least twice the speed of light.

Aware of Rees's model,[18] (Moffet et al. 1972)[22] concluded that their measurement presented evidence for relativistic expansion of this component.

This interpretation, although by no means unique, was later confirmed, and in hindsight it seems fair to say that their experiment was the first interferometric measurement of superluminal expansion.