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 of the University of Cologne. The scientists modeled several emission lines at the Atacama Large Millimeter Array (ALMA) and Very Large Telescope (VLT) observatories, to measure gas pressure in both jet-impacted clouds and ambient clouds.
Using the unprecedented measurements collected from this team, the researchers discovered that the jets significantly change the internal and external pressure of the molecular clouds in their path. This means that depending on which of the two pressures changes more, cloud compression, star formation activation, cloud dissipation and star formation delay are all possible in the same galaxy .
“Our results show that supermassive black holes, even though they are at the center of galaxies, could affect star formation in a galaxy-wide way,” Professor Dasyra explained. “Studying the impact of pressure changes on cloud stability was key to the success of this project. Once a few stars form in a wind, it’s usually very difficult to detect their signal above of the signal from all the other stars in the Galaxy that host the wind.”
This study was recently published in Nature Astronomy.
Formation of stars by condensation of gases
For decades, scientists have believed that supermassive black holes lie at the center of most galaxies in our Universe. When particles falling into these black holes are trapped by magnetic fields, they can be ejected outwards and travel far into galaxies in the form of huge, powerful jets of plasma. These jets are usually perpendicular to the galactic discs. However, in IC 5063, a galaxy 156 million light-years away, the jets propagate within the disk, interacting with clouds of cold, dense molecular gas. From this interaction it is theorized that compression of clouds impacted by the jet is possible, leading to gravitational instabilities and eventually star formation due to gas condensation.
During the experiment, the team used carbon monoxide (CO) and formyl cation (HCO+) emission provided by ALMA, and ionized sulfur and ionized nitrogen emission provided by VLT. They then used advanced and innovative astrochemical algorithms to identify the environmental conditions of the outflow and the surrounding medium.
These environmental conditions contain information about the strength of far-ultraviolet radiation from stars, the rate at which relativistic charged particles ionize the gas, and the mechanical energy deposited on the gas by the jets. Narrowing down these conditions revealed gas densities and temperatures descriptive of different parts of that galaxy, which were then used 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 at the University of Cologne and former postdoctoral researcher at the National Observatory of Athens.
Identify as many physical limitations as possible
A difficult part of the work was to meticulously identify as many physical constraints as possible on the examined range that each parameter could have. “In this way, we could obtain the optimal combination of physical parameters of the clouds at different locations in the Galaxy,” noted co-author Georgios Filippos Paraschos, a PhD student at the Max Planck Institute for Radio Astronomy in Bonn and a former master’s student . at the National and Kapodistrian University of Athens.
Pressures were not measured for just a few locations in IC 5063. Instead, they created maps of this and other quantities at the center of this galaxy. These maps allowed the authors to visualize how the properties of the gas change from one place to another due to the passage of the jet. The team is currently looking forward to the next big step in this project, which uses the James Webb Space Telescope for further investigations of the pressure in the outer layers of clouds, as evidenced by warm H2.
“We are really excited to get the data from JWST,” Professor Dasyra concluded. “Because they will allow us to study the interaction of the jet cloud with exquisite resolution.”