The Simultaneous Merging Of Giant Galaxies

An international research team led by scientists from Göttingen and Potsdam proved for the first time that the galaxy NGC 6240 contains three supermassive black holes. The unique observations, published in the journal Astronomy & Astrophysics, show the black holes close to each other in the core of the galaxy. The study points to simultaneous merging processes during the formation of the largest galaxies in the universe.

Massive Galaxies like the Milky Way typically consist of hundreds of billions of stars and host a black hole with a mass of several million up to several 100 million solar masses at their centres. The galaxy known as NGC 6240 is known as an irregular galaxy due to its particular shape. Until now, astronomers have assumed that it was formed by the collision of two smaller galaxies and therefore contains two black holes in its core. These galactic ancestors moved towards each other at velocities of several 100 km/s and are still in the process of merging. The galaxy system which is around 300 million light years away from us – close by cosmic standards – has been studied in detail at all wavelengths, and has so far been regarded as a prototype for the interaction of galaxies.

The irregular galaxy NGC 6240. New observations show that it harbors not two but three supermassive black holes at its core. The northern black hole (N) is active and was known before. The zoomed-in new high-spatial resolution image shows that the southern component consists of two supermassive black holes (S1 and S2). The green color indicates the distribution of gas ionized by radiation surrounding the black holes. The red lines show the contours of the starlight from the galaxy and the length of the white bar corresponds to 1000 light years.

Credit: P Weilbacher (AIP), NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)