An international team of researchers has captured the first-ever photographic evidence of a jet of material erupting from a collision between two spiral galaxies. This detection caught the beginning of a relativistic jet erupting, confirming that as a galaxy merger enters its crucial phase, the black holes at their core become more active releasing jets of material at almost the speed of light.
“For the first time, we have found two spiral- or disk-shaped galaxies on path for a collision that have produced a nascent, baby jet that has just started its life at the center of one of the galaxies,” lead author Dr Vaidehi Paliya, from the Deutsches Elektronen Synchrotron (DESY), said in a statement.
The team detected the gamma-ray emission, a telltale sign of the emergence of the jet, from galaxy TXS 2116−077, publishing their extraordinary observations in The Astrophysical Journal. The findings finally confirm that merging events can deliver enough material to a supermassive black hole to send it into an active state. The jet is just what happens next.
Almost every galaxy in the universe has a supermassive black hole at its center, the Milky Way included. But having an active one that produces jets is not that common. Black holes are not cosmic plug holes, sucking in anything and everything; they feed only when materials get close enough. During galaxy mergers, there’s plenty of opportunity for galactic gas to get a little bit to close to the core.
“It’s hard to dislodge gas from the galaxy and have it reach its center,” co-author Marco Ajello from Clemson University College of Science explained. “You need something to shake the galaxy a little bit to make the gas get there. The merging or colliding of galaxies is the easiest way to move the gas, and if enough gas moves, then the super-massive black hole will become extremely bright and could potentially develop a jet.”
However, it's not easy to see this taking place. In this case, the jet is pointing right at us and as it's still so young, it has not reached a level of overwhelming brightness yet. Some can easily outshine their galaxy, pumping out more energy in one second than our Sun produces in its entire lifetime.
“Typically, a jet emits light that is so powerful we can’t see the galaxy behind it,” adjunct professor Stefano Marchesi, also of Clemson, said. “It’s like trying to look at an object and someone points a bright flashlight into your eyes. All you can see is the flashlight. This jet is less powerful, so we can actually see the galaxy where it is born.”
Understanding galaxy mergers allow us to work out how galaxies evolve and change. It’s also a window into the future of the Milky Way. After all, a few billion years from now our galaxy will experience a similar collision with Andromeda.