Secrets of galactic butterfly revealed

Not all galaxies are neatly shaped, as this new NASA/ESA Hubble Space Telescope image of NGC 6240 clearly demonstrates. Hubble previously released an image of this galaxy back in 2008, but the knotted region, shown here in a pinky-red hue at the centre of the galaxies, was only revealed in these observations from Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys. NGC 6240 lies 400 million light-years away in the constellation of Ophiuchus (The Serpent Holder). This galaxy has an elongated shape with branching wisps, loops and tails. This mess of gas, dust and stars bears more than a passing resemblance to a butterfly and, though perhaps less conventionally beautiful, a lobster. This bizarrely-shaped galaxy did not begin its life looking like this; its distorted appearance is a result of a galactic merger that occurred when two galaxies drifted too close to one another. This merger sparked bursts of new star formation and triggered many hot young stars to explode as supernovae. A new supernova was discovered in this galaxy in 2013, named SN 2013dc. It is not visible in this image, but its location is indicated here. At the centre of NGC 6240 an even more interesting phenomenon is taking place. When the two galaxies came together, their central black holes did so too. There are two supermassive black holes within this jumble, spiralling closer and closer to one another. They are currently only some 3000 light-years apart, incredibly close given that the galaxy itself spans 300 000 light-years. This proximity secures their fate as they are now too close to escape each other and will soon form a single immense black hole. Links  Images of Hubble

NGC 6240 as seen by the Hubble Space Telescope. Image Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University


NGC 6240 is a galaxy with two supermassive black holes at its centre, leading to the conclusion that it was formed by the merging of two separate galaxies.

The two black holes are circling each other, getting closer with each orbit, and will eventually crash into one another.

Research into this phenomenon has revealed that gases ejected by the black holes and by stars in the galaxy may be responsible for cutting off the galaxy’s production of new stars.

These jets extend about 30,000 lightyears into space, forming the galaxy into a ‘butterfly’ shape.

Using the Hubble Space Telescope, the Very Large Telescope in Chile and Apache Point Observatory in New Mexico, a team from the University of Colorado Boulder have been able to build up a picture of the processes in the galaxy.

The butterfly’s northwest corner appears to be produced by streams of charged particles and gases emitted by stars.

The northeast corner appears to be the result of a single cone of gas ejected by the black holes. This happens as the black holes consume surrounding material, creating enormous amounts of energy that fires off powerful jets.

The Apache Point Observatory has teamed up with the Hubble Space Telescope and the Very Large Telescope in Chile to reveal the inner workings of two colliding galaxies © Wikimedia Commons
The Apache Point Observatory has teamed up with the Hubble Space Telescope and the Very Large Telescope in Chile to reveal the inner workings of two colliding galaxies © Wikimedia Commons

These two forces combined evict about 100 times the mass of the Sun in gases from the galaxy every year.

Normally the merging of galaxies is associated with the re-ignition of star formation, but in this case the black hole and stellar winds have slowed down the process by clearing away the gas and dust that form new stars.

“NGC 6240 is in a unique phase of its evolution,” says Julie Comerford, an assistant professor at Apache Point Observatory and a co-author of the study.

“It is forming stars intensely now, so it needs the extra strong kick of two winds to slow down that star formation and evolve into a less active galaxy.”

“We dissected the butterfly,” says study lead Francisco Müller-Sánchez of CU Boulder’s Department of Astrophysical and Planetary Sciences.


“This is the first galaxy in which we can see both the wind from the two supermassive black holes and the outflow of low ionization gas from star formation at the same time.”