An international team of astronomers used the Atacama Large Millimeter Array (ALMA) to create the most detailed image yet of the gas surrounding two supermassive black holes in a merging galaxy.
Four hundred million light-years away from Earth, in the constellation of Ophiuchus, two galaxies are crashing into each other and forming a galaxy we know as NGC 6240. This peculiarly-shaped galaxy has been observed many times before, as it is relatively close by. But NGC 6240 is complex and chaotic.
The collision between the two galaxies is still ongoing, bringing along in the crash two growing supermassive black holes that will likely merge as one larger black hole. Astronomers estimate it will take them another 10 to 20 million years to fuse completely; at that point, they’ll form the new galaxy called NGC 6240.
This is a special phenomenon as it takes over a billion years for a given pair of galaxies to merge. The two galaxies in question both contain a supermassive black hole in their center which is also expected to merge as well.
The team of scientists presented their research at the annual meeting of the American Astronomical Society in Honolulu, Hawaii, on Sunday. The findings also suggested that the black holes involved in other galaxy collisions could also be smaller than expected.
Until recently, astronomers believed that the supermassive black holes in the NGC 6240 galaxy had a mass equivalent to about 1 billion suns. The new photo suggests, however, that the black holes are about as massive as a few hundred million suns.
To understand what is happening within NGC 6240, astronomers want to observe the dust and gas surrounding the black holes in detail, but previous images have not been sharp enough to do that. New ALMA observations have increased the resolution of the images by a factor of ten – showing for the first time the structure of the cold gas in the galaxy, even within the sphere of influence of the black holes.
According to Ezequiel Treister, an associate professor at Pontificia Universidad Catolica in Santiago Chile, they observed a chaotic stream of gas with filaments and bubbles between the black holes. He added that they don’t know yet what causes these outflows and some of the gas was ejected outs with a speed of up to 500 kilometers per second.
Our own Milky Way galaxy is anticipated to merge with the nearby Andromeda galaxy in about four billion years.