ASTROPHYSICS: Faster than Light

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Science  29 Jun 2007:
Vol. 316, Issue 5833, pp. 1814d-1815d
DOI: 10.1126/science.316.5833.1814d

Faster-than-light motions can be seen as projected visual effects, even if actual movement at or above light speed is prohibited by relativity theory. In astrophysics, such superluminal motion is common in jets of very fast subatomic particles that emanate from massive black holes in the centers of galaxies. These jets reach out far beyond the galaxy itself, and individual blobs of relativistic plasma trapped by magnetic fields can be tracked by radio telescopes. When the jets are pointed toward an observer on Earth, the projected motions of the blobs on the sky make the jet appear to be expanding faster than light.

This illusion of superluminal motion normally appears toward the jet's base near the galaxy's central black hole, where the accelerations are greatest. However, Cheung et al. have now seen superluminal motion quite far (120 parsecs) from the central engine in the jets emerging from one of the most well-known nearby radio sources, the galaxy M87. From very high resolution radio observations, the authors attribute the phenomenon to a peripheral knot breaking apart and inducing apparent superluminal motion of its components. The same knot had been previously associated with a flaring x-ray source, suggesting a physical connection between the in situ acceleration of fast particles and high-energy emission flares that may operate in gamma-ray sources. — JB

Astrophys. J., astro-ph/0705.2448v2 (2007).

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