How does a supermassive black hole influence star formation?

A collaborative research team led by the National and Kapodistrian University of Athens, Greece, has investigated the influence of supermassive black holes on star formation.

Professor Kalliopi Dasyra of the National and Kapodistrian University of Athens, Greece, led the European research team which included Dr Thomas Bisbas from the University of Cologne. Scientists modelled several emission lines in the Atacama Large Millimetre Array (ALMA) and Very Large Telescope (VLT) observatory, to measure the gas pressure in both jet-impacted clouds and ambient clouds.

With the unprecedented measurements gathered from this equipment, researchers discovered that the jets significantly change the internal and external pressure of molecular clouds in their path. This means that, depending on which of the two pressures changes the most, the compression of clouds, the triggering of star formation, the dissipation of clouds, and the delaying of star formation are possible in the same Galaxy.

“Our results show that supermassive black holes, even though they are located at the centres of galaxies, could affect star formation in a Galaxy-wide manner,” explained Professor Dasyra. “Studying the impact of pressure changes on the stability of clouds was key to the success of this project. Once a few stars actually form in a wind, it is usually very hard to detect their signal on top of the signal of all other stars in the Galaxy hosting the wind.”

This study was recently published in Nature Astronomy.

Star formation due to gas condensation

For decades, scientists have believed that supermassive black holes lie at the centres of most galaxies in our Universe. When particles that were infalling onto these black holes are trapped by magnetic fields, they can be ejected outwards and travel far inside galaxies in the form of enormous and powerful jets of plasma. These jets are often perpendicular to galactic disks. However, in IC 5063 – a Galaxy 156 million light years away – the jets are actually propagating within the disk, interacting with cold and dense molecular gas clouds. It is theorised from this interaction that the compression of jet-impacted clouds is possible, leading to gravitational instabilities and eventually star formation due to the gas condensation.

During the experiment, the team utilised the emission of carbon monoxide (CO) and formyl cation (HCO+) provided by ALMA, and the emission of ionised sulphur and ionised nitrogen provided by VLT. They then used advanced and innovative astrochemical algorithms to pinpoint the environmental conditions in the outflow and in the surrounding medium.

These environmental conditions contain information about the strength of the far-ultraviolet radiation of stars, the rate at which relativistic charged particles ionise the gas, and the mechanical energy deposited on the gas by the jets. Narrowing down these conditions revealed the densities and gas temperatures descriptive of different parts of this Galaxy, which were then utilised to provide pressures.

“We have performed many thousands of astrochemical simulations to cover a wide range of possibilities that may exist in IC 5063,” said co-author Dr Thomas Bisbas, DFG Fellow of the University of Cologne and former postdoctoral researcher at the National Observatory of Athens.

Identifying as many physical constraints as possible

A challenging part of the work was to meticulously identify as many physical constraints as possible to the examined range that each parameter could have. “This way, we could get the optimal combination of physical parameters of clouds at different locations of the Galaxy,” noted Mr Georgios Filippos Paraschos, co-author, PhD student at the Max Planck Institute for Radio Astronomy in Bonn, and former Master’s student at the National and Kapodistrian University of Athens.

Pressures were not just measured for a few locations in IC 5063. Instead, maps of this and other quantities in the centre of this Galaxy were created. These maps allowed the authors to visualise how the gas properties transition from one location to another because of the jet passage. The team is currently looking forward to the next big step of this project, which is utilising the James Webb Space Telescope for further investigations of the pressure in the outer cloud layers, as probed by the warm H2.

“We are truly excited about getting the JWST data,” concluded Professor Dasyra. “As they will enable us to study the jet-cloud interaction at an exquisite resolution.”

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