The black hole at the edge of galaxy NGC 7793, twelve million light years from Earth, has been found to be doing something rare - emitting powerful jets of particles of a total length of 1,000 light years.  The energy produced by matter falling into a black hole this size is usually transformed into X-rays, not into jets, but this one is the exception - a miniature version of certain supermassive black holes present in the active nuclei of galaxies.

The two jets of matter that they observed are the most powerful ever discovered for this type of black hole, resulting from the collapse of a star. The jets push back the interstellar medium, hollowing out a large bubble of relativistic particles and very hot gases around the black hole. This bubble radiates in the optical, X-ray and radio wavelengths: it has been expanding for 200,000 years and now measures 1,000 light years in diameter. It is inflating at a speed close to one million kilometers per hour.

Until now, it was thought that the energy produced by a black hole swallowing matter was mainly emitted in the form of radiation, particularly X-rays. This discovery is all the more surprising as it shows that certain black holes can emit much more energy in the form of jets of particles. These jets, when they come into contact with interstellar gas, trigger a shockwave that causes heating and accelerates the expansion of the bubble.

In the case of the active nuclei of galaxies, which contain supermassive black holes, jets of particles are also observed streaming in the intergalactic medium. This discovery should therefore elucidate the mechanisms by which these jets are produced and their impact on the near and distant environment of the black hole.

Citation: 'A 300 parsec long jet-inflated bubble around a powerful microquasar in the galaxy NGC 7793', Nature, 8 July 2010, M. W. Pakull, R. Soria and C. Motch