NGC 6240 (also designated VV 617 and IC 4625) is pair of merging galaxies about 400 million light-years away in the constellation Ophiuchus. The pair is moving away from us with a speed of about 7339 km/sec.
This image shows them in a rare, short-lived phase of their evolution just before they merge into a single, larger galaxy. The prolonged, violent collision which began about 30 million years ago, has resulted in this butterfly- or lobster-shaped galaxy with two distinct active galactic nuclei.
The merging process triggered dramatic star formation, sparked numerous supernova explosions and spew forth tidal tails of stars, gas, and dust. NGC 6240 is therefor a prime example of a “starburst” galaxy in which stars are forming, evolving, and exploding at an exceptionally rapid rate due to a relatively recent merger. The collision also created huge amounts of heat — turning NGC 6240 into an active ultraluminous infrared galaxy.
Radio, infrared, and optical observations led to the discovery of two orbiting supermassive black holes, about 3,000 light-years apart, which will drift toward one another and eventually merge together into one even larger supermassive black hole. This detection of a binary black hole supports the idea that black holes grow to enormous masses in the centers of galaxies by merging with other black holes.
Because of the distance and the finite speed of light, the predicted merger of supermassive black holes in NGC 6240 has likely already occurred long ago. But we won’t know about it for some tens to hundred millions of years.
Image Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)