Discovery of Gamma Rays from the Edge of a Black Hole

Press Release of the Max Planck Society

Oct 26, 2006

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H.E.S.S. discovers drastic variations of very-high-energy gamma rays from the central engine of the giant elliptical galaxy M 87

The astrophysicists of the international H.E.S.S. collaboration report the discovery of fast variability in very-high-energy (VHE) gamma rays from the giant elliptical galaxy M 87. The detection of these gamma-ray photons - with energies more than a million million times the energy of visible light - from one of the most famous extragalactic objects on the sky is remarkable, though long-expected given the many potential sites of particle acceleration (and thus gamma-ray production) within M 87. Much more surprising was the discovery of drastic gamma-ray flux variations on time-scales of days. These results, for the first time, exclude all possible options for sites of gamma-ray production, except for the most exciting and extraordinary one: the immediate vicinity of the super-massive black hole which is located in the centre of M 87 (Science Express, October 26, 2006).

Fig. 1: Image of radio galaxy M 87 seen in visible light. The central region, from which the VHE gamma rays are seen, is located in the upper left part of the image and the relativistic plasma jet extends to the bottom right.(HST)

An international team of astrophysicists from the H.E.S.S. collaboration has announced the discovery of short-term variability in the flux of very-high-energy (VHE) gamma rays from the radio galaxy M 87. In Namibia, the collaboration has built and operates a detection system, known as Cherenkov telescopes, which permits these gamma rays to be detected from ground level (see notes). Pointing this system at a nearby galaxy, M 87, the team has detected VHE gamma rays over the past four years. The real surprise is, however, that the intensity of the emission can be seen to change drastically within a few days on occasion.

The giant radio galaxy M 87

[editor's note: this is a reference image of M87 from my own files.]

This galaxy, located 50 million light-years away in the constellation Virgo, harbours a super-massive black hole of 3 thousand million solar masses from which a jet of particles and magnetic fields emanates. However, unlike for previously-observed extragalactic sources of VHE gamma rays - known as Blazars - the jet in M 87 is not pointing towards the Earth but is seen at an angle of about 30