Since galaxies change slowly, it's unsurprising we find ones that are merging so fascinating – they give us a spectacular snapshot of this galactic evolution. Now researchers have peered into the heart of a nearby merger known as NGC 6240.
As reported in Nature, astronomers have seen for the first time the emissions of both supermassive black holes at the core of NGC 6240. Galaxies usually have just one at their center, but since this object hasn’t finished merging yet, the black holes are yet to collide.
The interactions between themselves and the materials from the original galaxies have produced quite the incredible feature – a gas cloud 30,000 light-years across in the shape of a butterfly in flight. The butterfly is produced by the hot "winds" released by the black holes in combination with material ejected from stars. The butterfly is going to have a big effect on the galaxy as a whole, stopping it from forming new stars.
“We dissected the butterfly,” lead author Dr Francisco Müller-Sánchez of CU Boulder said in a statement. “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."
The impressive feat was possible by using three different telescopes: the Hubble Space Telescope, the Very Large Telescope, and the Apache Point Observatory. The team were able to identify the origin of the different gas, with the northeast corner of the butterfly dominated by a cone of gas from the black holes and the northwest bit caused by stars.
“The data from these three telescopes allowed us to determine the location and velocity of different types of gas in the galaxy,” added co-author Rebecca Nevin, also at CU Boulder. “This helped us uncover two winds – one that is driven by dual supermassive black holes, and one that is driven by star formation.”
The winds eject 100 times the mass of the Sun in gas from the galaxy every year. This is a substantial loss and it matches the number of new stars that the galaxy is producing. As the galaxy loses gas, it won’t be able to sustain this high rate of star formation. This is known in a galaxy merger as negative feedback.
“NGC 6240 is in a unique phase of its evolution,” co-author professor Julie Comerford, stated. “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.”
NGC 6240 was formed by the collision of two similar-sized galaxies. It is located 400 million light-years from Earth.
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