Radio Imaging of the Very-High-Energy γ-Ray Emission Region in the Central Engine of a Radio Galaxy

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Science  24 Jul 2009:
Vol. 325, Issue 5939, pp. 444-448
DOI: 10.1126/science.1175406

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Black Hole Energy Boost

More than 20 galaxies are known to emit photons with energies a trillion times higher than those of visible light, but it is not known where this emission originates. These galaxies are part of a class of active galactic nuclei believed to harbor supermassive black holes in their centers from which relativistic plasma jets emerge, reaching out many thousands of light years into the intergalactic medium. Acciari et al. (p. 444, published online 2 July; see the Perspective by Begelman) present simultaneous radio and very-high-energy γ-ray observations of the nearby active galaxy Messier 87, revealing very-high-energy flaring activity accompanied by a radio flare originating from the core of the galaxy. The findings imply that the highest energy emission from active galaxies has its origin in the immediate vicinity of the black hole.


The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 1012 electron volts and are bright sources of very-high-energy (VHE) γ-ray emission, it is not yet known where the VHE emission originates. Here we report on radio and VHE observations of the radio galaxy Messier 87, revealing a period of extremely strong VHE γ-ray flares accompanied by a strong increase of the radio flux from its nucleus. These results imply that charged particles are accelerated to very high energies in the immediate vicinity of the black hole.

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