Superluminal motion
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In astronomy, superluminal motion is the apparently faster-than-light motion seen in some radio galaxies, quasars and recently also in some galactic sources called microquasars. All of these sources are thought to contain a black hole, responsible for the ejection of mass at high velocities.
When first observed in the early 1980s, superluminal motion was taken to be a piece of evidence against quasars having cosmological distances. Although a few astrophysicists still argue for this view, most believe that apparent velocities greater than the velocity of light are optical illusions and involve no physics incompatible with the theory of special relativity.
Explanation
This phenomenon is caused because the jets are travelling very near the speed of light AND at a very small angle towards the observer. Because at every point of their path they are emiting light and due to their high velocity; the light they emit does not approach the observer much quicker than the jet itself. This causes the light emitted over hundreds of years of travel to not have hundreds of lightyears of distance between it, the light thus arrives at the observer over a much smaller time period (ten or twenty years) giving the illusion of faster than light travel.
This explanation depends on the jet making a sufficiently narrow angle with the observer's line-of-sight to explain the degree of superluminal motion seen in a particular case.[1]
Superluminal motion is often seen in two opposing jets, one moving away and one toward Earth. If Doppler shifts are observed in both sources, the velocity and the distance can be determined independently of other observations.
Some contrary evidence
As early as 1983, at the "superluminal workshop" held at Jodrell Bank, referring to the seven then-known superluminal jets,
Schilizzi ... presented maps of arc-second resolution [showing the large-scale outer jets] ... which ... have revealed outer double structure in all but one (3C 273) of the known superluminal sources. 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.[2]
In other words the jets are evidently not, on average, close to our line-of-sight. (Their apparent length would appear much shorter if they were.)
In 1993, Thomson et al. suggested that the (outer) jet of the quasar 3C 273 is nearly perpendicular to our line-of-sight. Superluminal motion of up to ~9.6c has been observed along the (inner) jet of this quasar.[3]
Superluminal motion of up to 6c has been observed in the inner parts of the jet of M87. To explain this in terms of the "narrow-angle" model, the jet must be no more than 19° from our line-of-sight.[4] But evidence suggests that the jet is in fact at about 43° to our line-of-sight[5]. The same group of scientists later revised that finding and argue in favour of a superluminal bulk movement in which the jet is embedded[6].
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.[7]
Laser Ranging
NASA's lunar laser ranging experiment is the first specific and precise test of the invariance of 'c' and Special Relativity. The first two papers were published in Dec. 2009.[8]. [9]. The results are inconsistent with either SR or Lorentz invariance of 'c'. They are consistent with GPS data when corrected to consistently account for the Sagnac effect[3]. Measured speed appeared superluminal, exceeding canonical value by 200ms. "just the speed of the observatory along the line of sight due to rotation during measurement." If 'c' were to remain invariant a preferred frame would be required "but tied to what physical system." In this case an observer in the preferred frame could measure the apparent superluminal motion of light travelling at 'c' within another frame in relative motion, as the Discrete Field Model, and would suggest an alternative explanation for the gas jets of galaxy M87 (see below).
Discrete Field Model
(DFM) [10] [11] This 2009 model uses oscillating halo and shock particles to Doppler shift EM waves (as FM radio). This would allow equivalence with a preferred frame or background field. Fields are tied to all physical matter in relative motion, as Einstein said of space in 1952; "it must now be remembered that there is an infinite number of spaces, which are in motion with respect to each other." The NASA Lunar ranging results of Dec '09.[12]. [13] precisely conform to the DFM's predictions, which can apparently also explain lensing anomalies. It conforms fully to SR's postulates, and the the NASA ranging data. It is close to and allows the Fresnel/Stokes etc. 'Ether Drag' theory. Light can only be measured at 'c', but may be observed from a detached 3rd frame as Superluminal.
Messier 87 Gas Jets
An alternative explanation for the Gas Jets.[14] moving at 6c is derived from the Discrete Field Model and is consistent with the NASA Lunar Ranging results (above). The magnetic field of the super massive rotating black hole will be contorted to a 'tube' at the poles, ejecting the particles. The jet is proposed as a moving 'field' gradually slowing and diffusing, but with new particles travelling in its core at close to 'c' within its own moving frame, and more new ones at 'c' in their frame. Newer core particles would be more radiant. From the Hubble space telescopes 'preferred' frame they would in this case appear to be moving at 6c, but none would exceed 'c' in the quantum field they are moving within.
History
In 1966 Martin Rees predicted (Nature 211, 468) that "an object moving relativistically in suitable directions may appear to a distant observer to have a transverse velocity much greater than the velocity of light".
A few years later (in 1970) such sources were indeed discovered as very distant astronomical radio sources, such as radio galaxies and quasars. They were called superluminal (lit. "above light") sources. The discovery was a spectacular result of a new technique called Very Long Baseline Interferometry, which allowed astronomers to determine positions 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 and could be up to 6 times the speed of light.
In 1994 a Galactic speed record was obtained with the discovery of a superluminal source in our own Galaxy, the cosmic x-ray source GRS 1915+105. The expansion occurred on a much shorter timescale. Several separate blobs were seen (I.F. Mirabel and L.F. Rodriguez, Nature 371, 48, "A superluminal source in the Galaxy") to expand in pairs within weeks by typically 0.5 arcsec. Because of the analogy with quasars, this source was called a microquasar.
Notes
- ^ See http://www.mhhe.com/physsci/astronomy/fix/student/chapter24/24f10.html for a graph of angle versus apparent speeds for two given actual relativistic speeds.
- ^ (R Porcas, "Superluminal motion: Astronomers Still Puzzled", Nature, vol.302, no.28, April 1983, p.753)
- ^ R D Thomson, C D Mackay and A E Wright, "Internal structure and polarization of the jet of the quasar 3C273", Nature, vol.365, 9 Sept. 1993, p.135 (cf. p.134); T J Pearson et al., "Superluminal expansion of quasar 3C273", Nature, vol.290, 2 April 1981, p.365-; Davis, Unwin, Muxlow, "Large-scale superluminal motion in the quasar 3C273", Nature, vol.290, 5 Dec. 1991, pp.374-6.
- ^ J A Biretta et al., "Formation of the radio jet in M87 at 100 Schwarzschild radii from the central black hole", Nature, vol.401, 28 October 1999 (pp.891-2), p.* ; Biretta, W B Sparks, F Maccheitto, "Hubble Space Telescope Observations of Superluminal Motion in the M87 Jet", Astrophysical Journal, vol.520, pp.621-6, 1 August 1999.
- ^ Biretta, Zhou, Owen, "Detections of Proper Motions in the M87 Jet", Astrophys. Journal, vol.447, 1995, p.582.
- ^ Biretta, Sparks, Machetto "Hubble Space Telescope Observations of Superluminal Motion in the M87 Jet", Astrophys. Journal, vol.520, 1999, p.621.
- ^ See, e.g., J A Biretta et al., "Formation of the radio jet in M87 at 100 Schwarzschild radii from the central black hole", Nature, vol.401, 28 October 1999 (pp.891-2).
- ^ Experimental Basis for Special Relativity in the Photon Sector. 18 Dec '09. Daniel Y. Gezari[1]
- ^ Lunar Laser Ranging Test of the Invariance of c. D Gezari. NASA. Dec '09.[2]
- ^ Doppler Assisted Quantum Unification Allowing Relativistic Invariance. Sept 09. Peter A Jackson[3]
- ^ Lensing and Galactic Mass Anomaly Solution From DFM Shock Model Peter A Jackson 19 Dec '09.[4]
- ^ Experimental Basis for Special Relativity in the Photon Sector. 18 Dec '09. Daniel Y. Gezari[5]
- ^ Lunar Laser Ranging Test of the Invariance of c. D Gezari. NASA. Dec '09.[6]
- ^ J A Biretta et al., "Formation of the radio jet in M87 at 100 Schwarzschild radii from the central black hole", Nature, vol.401, 28 October 1999 (pp.891-2), p.* ; Biretta, W B Sparks, F Maccheitto, "Hubble Space Telescope Observations of Superluminal Motion in the M87 Jet", Astrophysical Journal, vol.520, pp.621-6, 1 August 1999.