The jets which are shot away into space by the supermassive black hole in the centre of a galaxy, clear gas away from the galaxy. The first clear evidence of this was obtained by a team led by Raffaella Morganti (ASTRON, University of Groningen). The results will be published in Science on the 6th of September.
Published by the editorial team, 6 September 2013
Astronomers have been puzzled by the fact that many galaxies in the Universe seem to be depleted of their gas and are therefore unable to form any new stars. Fast outflows of gas have been observed in the past, but the mechanism driving these outflows was not understood. The suspicion that the powerful plasma jets that are shot into space by the central supermassive black hole are responsible for the expulsion of the gas has now been confirmed.
The nucleus of the galaxy 4C12.50 was observed with ultra-high resolution using a global Very Long Baseline Interferometry (VLBI) network, an array of radio telescopes across different continents which form a telescope the size of the earth. The high-resolution images resulting from the VLBI observations allowed the team to pin down the location of the gas outflow and to determine the speed with which the gas leaves the galaxy.
Morganti: “We suspected the importance of these radio jets from previous studies using for example the Westerbork Synthesis Radio Telescope. With these observations at much higher resolution we were finally able to map the distribution of the gas. It could not have been in better agreement with our expectations!”
The astronomers found that the gas is flowing out of the galaxy at a velocity of 1000 kilometers per second. Despite the strong push received from the jet, the temperature of the gas is low. “This was quite unexpected,” says coauthor Tom Oosterloo (ASTRON, University of Groningen). “But this is exactly what is needed to make theory of galaxy formation and observations to agree. It is in particular cold gas that is the fundamental building block of new stars, but this gas is being expelled by the jet.”
Using a global array of radio telescopes we are able to peek into the nucleus of 4C12.50, located two billion light years from the earth. Zsolt Paragi, astronomer at JIVE and coauthor: “These observations, combining telescopes from both the European VLBI Network and the Very Long Baseline Array in the U.S., allowed us to trace gas at the immediate proximity – just 300 light years – of the black hole of 4C12.5.”
The success of the observations means that VLBI is a suitable technique to study the effect of the super massive black hole on the gas in its vicinity. Morganti will use this technique to study more objects where gas outflows are suspected to exist in the project ‘Exploiting new radio telescopes to understand the role of AGN in galaxy evolution’, for which Morganti received a ERC Advanced Grant last year.
Optical image (blue) of the galaxy 4C12.50. The inset shows a zoom in of the plasma jet and the cold gas (orange). The gas is distributed in a compact cloud (dark orange) and filaments (light orange) as result of the strong impact with the plasma jet. Credit: optical: HST/STSci/Tadhunter et al.; radio: VLBI, Morganti et al. 2013.
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.
The Joint Institute for VLBI in Europe (JIVE, www.jive.nl) is a scientific foundation with a mandate to support the operations of the European VLBI Network (EVN, www.evlbi.org). For this purpose it maintains, operates and develops the EVN data correlator, a powerful supercomputer that combines the signals from radio telescopes located across the planet.
Prof. dr. Raffaella Morganti, ASTRON, RuG
Prof. dr. Tom A. Oosterloo, ASTRON, RUG
Dr. Zsolt Paragi
Radio Jets Clearing the Way Through a Galaxy: Watching Feedback in Action,
R. Morganti, J. Fogasy, Z. Paragi, T. Oosterloo, M. Orienti, Science, 6 September 2013