Supermassive black holes at the centres of galaxies are known to give rise to fast moving jets of relativistic particles that can traverse large distances through the galaxy and beyond. An international team of astronomers, including Prof. Dipanjan Mukherjee from IUCAA, have now shown that even a relatively weak jet from a supermassive black hole can clear the nuclear region of the galaxy of its gas.

The study, led by astronomers in the Netherlands, Suma Murthy, Raffaela Morganti and Tom Osterloo from the Netherlands Institute for Radio Astronomy (ASTRON), involved observing the motions of molecular gas in the galaxy B2 0258+35, using the NOEMA (Northern Extended Millimetre Array) telescopes. The team also included Pierre Guillard from the Institut d'Astrophysique de Paris, France, Alexander Wagner from the University of Tsukuba, Japan, Dipanjan Mukherjee from IUCAA, India and Geoffrey Bicknell from the Australian National University, Australia, who aided in the interpretation of the observed results and comparison with theoretical simulations performed by Prof. Mukherjee and colleagues in 2018

Astronomers have found that gas is steadily being blown away from the central regions of the galaxy, pushed by the relativistic jet. Although the power of the jet observed in radio wavelengths is moderate, it is still capable of clearing out nearly 75% of the central gas reservoir. This is the first unambiguous detection of a relativistic jet from a supermassive black hole removing the gas in a galaxy. Competing mechanisms that can also cause such outflows have been ruled out in this case. The ejected gas is however is not fast enough to completely escape the galaxy, and will eventually fall back in.

This research showcases strong synergy between observational results and the simulations of relativistic jets interacting with a dense interstellar medium of a galaxy, carried out by Prof. Mukherjee in 2018. The results of these simulations have been compared with the observations of B2 0258+35 in this work. Astronomers find remarkable similarities between the predictions of the simulated gas kinematics and the observed dynamics of the molecular gas.

Relativistic jets from supermassive black holes have long been suspected of driving the evolution of galaxies. However, so far, only their impact as a source of heating the circum-galactic atmosphere has been considered. Numerical simulations by Prof. Mukherjee and colleagues have, on the other hand, predicted strong influence of such jets on the host galaxy itself, before breaking out to larger scales. Although previous observational campaigns have found putative signatures of jets injecting energy in the interstellar medium of galaxies, effect of radiation from the central black hole could not be completely excluded. The new results from this study provide definitive proof that relativistic jets can indeed substantially affect the host galaxy's gas. This may have significant impact on how and over what timescales stars are formed in such galaxies; topics of active current research. Additionally, lower power jets are found more frequently than their higher power counterparts. Hence, if such low power jets have the potential to influence their host, relativistic jets from such black holes are expected to play an important role in the evolution of their host galaxies, contrary to what has been thought before.

Research contacts:

Prof. Dipanjan Mukherjee Assistant Professor, Inter University Center for Astronomy and Astrophysics, Tel.: +91-20-25604-210 (Off.) E-mail: dipanjan_at_iucaa.in

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