The system Abell 2384 retains the visible consequences of its dramatic past. The two galaxy clusters that make up the system collided several hundred million years ago. The clusters passed through each other, affecting the galaxies and producing an incredible bridge of hot gas between the two groups.
Recent observations have revealed that the bridge is being hit by particles driven into intergalactic space by a supermassive black hole, bending it in the process. This rare event, described in the Monthly Notices of the Royal Astronomical Society, is a window into the evolution of galaxy clusters.
The team spotted the curious bridge using the Giant Metrewave Radio Telescope in India as well as X-ray observations from NASA’s Chandra and ESA's XMM-Newton. The cause is an active supermassive black hole in a galaxy at the outskirt of the southern cluster that's releasing two jets of particles in opposite directions. One of the jets is pointed at the bridge and is changing its shape.
The bridge extends over 3 million light-years and is sizeable in mass at about 6 trillion Suns. That’s about four times the mass of our own galaxy, the Milky Way. The jet is also far away from its source, stretching for about 1.2 million light-years from its black hole before colliding with the bridge.
Interactions are common among cosmic objects. Galaxies merge with each other and so do clusters of galaxies. Astronomers envision the latter as a cosmic accordion – they go through each other, stretching out the system, and then come back and out again, until they eventually relax into a single cluster. When clusters of galaxies collide, the individual galaxies don't necessarily hit each other. Instead, they are more like two bird flocks coming together as one rather than a car crash.
However, this doesn't mean that the individual galaxies are left unscathed. Observations of Abell 2384 show many spiral galaxies in the cluster are no longer forming stars anymore. This is because the interaction has stripped them of precious gas to form new stars. Now, some of that same gas is forming the brilliant bridge that we can see in these observations.