Markarian 739 and its double core
At the heart of every galaxy lies a monster, a colossal gravity well that sports a mass hundreds of millions, or even many billions of times the mass of our Sun. These monsters are the supermassive black holes that dominate the cores of their host galaxies, with event horizons even bigger than our solar system. They’re either frantically feeding on infalling gas, stars, planets, whatever…it’s all good. Or they’re quiet and sedate like the black hole at the centre of our Milky Way. They have a mass far in excess of the stellar mass black holes that we find living in galaxy spiral arms, produced when massive stars end their lives in a supernova or hypernova. The supermassive variety are also proportional to the size of their home galaxy, large galaxy…large black hole, small galaxy…smaller black hole.
When one of these behemoths is gorging on material at a tremendous rate, a flattened disk of in falling gas and material forms around the black hole. Also two narrow jets of particles are produced that travel at near light speed from above and below the black hole. These jets are the work of the powerful magnetic fields surrounding the accretion disk, that can blast the jets to a distance much further than the entire diameter of the host galaxy. The black hole’s accretion disk heats up to extremely high temperatures as the material spirals inwards, even undergoing nuclear reaction. The disk can release vast amounts of light and other radiation, producing events such as quasars, blazars, or seyfert galaxies. All produced in what is known as an active galactive nucleus (AGN), underpinning all these phenomena are active supermassive black holes.
So what’s special about galaxy Markarian 739, or NGC 3758 ? Well to be more precise this object 425 million light years away is actually two galaxies in the process of merging together. You can clearly see the two bright cores of the original galaxies as they near each other in the image above. Active galactic nuclei only account for about 1 percent of all supermassive black holes, so they’re quite rare beasts.
Astronomers had known that Markarian 739 had an AGN in the eastern most of the bright cores, but now thanks to Nasa’s Swift Satellite and the Chandra X-ray Observatory, another AGN has been found.
A distance of 11,000 light years separate the two black holes, which is a thousand or so light years closer than the Orion Nebula is to Earth. This is only the second double AGN found within half a billion light years, the other being Galaxy NGC 6240.
Article, 11th June 2011
