An article published in the journal “Nature” describes a research on the formations similar to the wings of a butterfly in the galaxy NGC 6240. A team of researchers at the University of Colorado Boulder combined observations made with the Hubble Space Telescope, the VLT in Chile and the Apache Point Observatory in New Mexico to study that galaxy by concluding that those particular formations are generated by different forces, in one case by a pair of supermassive black holes.
The studies of galaxies enabled to ascertain that it’s normal for them to have a supermassive black hole at their center. However, when two galaxies merge, for a while they can have two supermassive black holes inside them that slowly get closer until they start orbiting each other in an ever closer way, a process that ends with their merger.
Approximately 400 million light years from Earth, the galaxy NGC 6240 is a case of galaxy merger still in progress. When the stars and black holes of two galaxies exert their gravitational pull among them the shape of the resulting galaxy changes for many millions of years, until the process ends with a new balance. If those are common galaxies, the two supermassive black holes can have strong influences on the result and the case of NGC 6240 is very special.
The team led by Francisco Müller-Sánchez used observations made with the Hubble Space Telescope, the Very Large Telescope (VLT) in Chile and the Apache Point Observatory in New Mexico to study the situation in that galaxy merger. Their conclusion is that there are two forces at work: stellar winds emitted by the stars through various processes and the emissions of the pair of supermassive black holes that we see while they’re orbiting each other.
Continuing with the butterfly image, the north-west wing of NGC 6240 is generated by stellar winds while the north-east wing is generated by a cone of gas ejected by the pair of supermassive black holes. These emissions extend for about 30,000 light years and the researchers estimate that every year the forces at work generate about one hundred solar masses of gas.
Those outflows can have important consequences on the galaxy. A galaxy merger triggers the birth of new stars because the gas clouds within the original galaxies get compressed and enough concentrations are formed in various regions to generate new star systems. However, the outflows noted in NGC 6240 push a lot of gas away, which slows down that star formation phenomenon.
The galaxy merger process in progress will continue for millions of years from our point of view and the merger of the two supermassive black holes will also take place only in millions of years. The objects inside NGC 6240 are crossing distances of many light-years so astronomers can keep on following the evolution of those processes for a very long time.