The Eddington luminosity is the exact brightness a black hole has when the outwards and inwards forces on it balance. It may seem strange to talk about the brightness of a black hole, as usually we think of them as not letting anything – including light – escape their gravitational pull, but in reality this is not the case. Black holes do draw in all the material that surrounds them, but as they do this they become surrounded by disks of gas in a process known as accretion. This gas can become so hot that it emits vast amounts of X-rays.
So, black holes above the Eddington luminosity emit light radiation that is more powerful that their gravitational pull. Such black holes are rare and not much is known about them. Very bright X-ray sources are the most likely candidates to harbour these types of black hole, so researchers from the University of Strasbourg and University College London went looking for X-ray sources around unusually large remnants of supernovae. They found what they were looking for in a galaxy not too far away…
There is a spiral galaxy known as NGC 7793 12.7 million light years away from us in the Sculptor constellation. In one of its spiral arms is a very bright nebula with a power source that is almost certainly a black hole with a luminosity above the Eddington limit. Unusually for a black hole such as this, it appears to dispel most of its accretion-generated energy mechanically rather than through radiation. This means that coming out of the black hole’s disk in opposing directions are two huge jets of very energetic particles – something that has not been seen very often before in these types of nebulae. These jets are the most powerful of their kind ever found, and are ten thousand times more energetic than the X-rays emitted from the core of the black hole. Around the jets has formed a bubble of plasma that is a thousand light years long.
Above is an image of the bubble of plasma that surrounds the jets. In the image you can see the core and the northern and southern hotspots, where the jets interact with the ambient medium. Jets such as these are needed to explain many things in astrophysics, but their origin is not yet well understood.
Pakull, M., Soria, R., & Motch, C. (2010). A 300-parsec-long jet-inflated bubble around a powerful microquasar in the galaxy NGC 7793 Nature, 466 (7303), 209-212 DOI: 10.1038/nature09168