New research has solved a long-standing mystery surrounding the evolution of galaxies, which deepens our understanding of the future of the Milky Way. The supermassive black holes in the cores of some galaxies drive massive outflows of molecular hydrogen gas. As a result, most of the cold gas is expelled from the galaxies. Since cold gas is required to form new stars, this directly affects the galaxies’ evolution.
These outflows are now a key ingredient in theoretical models of the evolution of galaxies, but it has long been a mystery as to how they are accelerated.
The study, led by Clive Tadhunter (Sheffield University) and including Raffaella Morganti, Tom Oosterloo (ASTRON/Kapteyn Institute Groningen University) and Raymond Oonk (ASTRON/Leiden University), provides the first direct evidence that the molecular outflows are accelerated by energetic jets of electrons that are moving at close to the speed of light. Such jets are propelled by the central supermassive black holes.
Using the ESO Very Large Telescope in Chile to observe the nearby galaxy IC5063, the researchers found that the molecular hydrogen gas is moving at extraordinary speeds — 1 million kilometers per hour — at the locations in the galaxy where its jets are impacting regions of dense gas.
These findings help us further understand the eventual fate of our own galaxy, the Milky Way, which will collide with neighbouring galaxy Andromeda in about 5 billion of years. As a result of this collision, gas will fall to the centre of the remnant of this collision, but the jets coming from the central supermassive black hole will, in a way similar to what is now observed in IC 5063, eject the gas from the system, preventing the formation of new stars and growth of the newly formed galaxy.
Clive Tadhunter, from the University's Department of Physics and Astronomy, said: "Much of the gas in the outflows is in the form of molecular hydrogen, which is fragile in the sense that it is destroyed at relatively low energies. I find it extraordinary that the molecular gas can survive being accelerated by jets of highly energetic particles moving at close to the speed of light."
“We suspected that the molecules must have been able to reform after the gas had been completely upset by the interaction with a fast plasma jet.” says Morganti. “Our direct observations of the phenomenon have confirmed that this extreme situation can indeed occur. Now we need to work at describing the exact physics of the interaction”.
The results are published in Nature on the 6th of July and they are connected to the project ‘Exploiting new radio telescopes to understand the role of AGN in galaxy evolution', for which Morganti received from the European Research Council an Advanced Grant of 2.5 Meuro last year.
ASTRON is the Netherlands Institute for Radio Astronomy (www.astron.nl). Its mission is to make discoveries in radio astronomy happen, via the development of novel and innovative technologies, the operation of world-class radio astronomy facilities, and the pursuit of fundamental astronomical research.