Supernova shells around supermassive black holes

Galactic centers, also called galactic nuclei, are extremely dense regions at the center of galaxies. It is assumed that each galactic center is the host of a supermassive black hole. When matter is accreted on this supermassive black hole, it gets heated and radiates a colossal amount of energy in the entire electromagnetic spectrum. During these periods, the nucleus is called active, and the entire region classified as an Active Galactic Nuclei, or AGN.

Star formation and supermassive black hole growth are known to be strongly connected. It is measured that in the nearby Universe the mass of the SMBH, which is the result of their successive accretion events, is directly proportional to the mass of the stellar bulges, which is the result of successive star formation events. More directly, it is observed that the average star formation rate along cosmic times correlates very strongly to AGN activity, as illustrated by the famous cosmic noon (z ~ 2-3) when both phenomena peaked.

To this day, the nature of this connection remains unclear. Many mechanisms connect nuclear star formation and AGN activity, probably cooperating to produce the observed correlations. First of all, both phenomena can result from a large flow of matter toward the region, and they are regularly observed simultaneously in post-merger situations.  Second, by injecting turbulent viscosity in the ISM, circumnuclear star formation can trigger the inflow of matter toward the central supermassive black hole. Finally, the AGN is expected to impact surrounding star formation: locally, shocks from the outflowing material can trigger the collapse of molecular clouds and the subsequent star formation (positive feedback); on larger time and spatial scales, the AGN injection of energy in the galaxy will heat the ISM, preventing the collapse of molecular clouds, and quenching star formation (negative feedback). We investigate a new mechanism, in which star formation could locally trigger AGN activity by depositing material in the immediate vicinity of the SMBH through expanding supernovæ shells.

For this purpose, we simulate the evolution of supernovæ shells in various galactic center environments and measure the amount of matter they can deposit in the central parsec around supermassive black holes. Our first results, focused on the Milky Way's galactic center, are conclusive and indicate that supernovæ can have a net positive impact on the growth of Sgr A*. We are in the process of generalizing this result, by including more complex ISM conditions to our analysis as well as other nearby galactic centers.

- Simplified hydrodynamics with the thin-shell approximation code RING
- Complete hydrodynamics simulations with the FLASH hydrocode
- High angular resolution Near-Infrared spectroscopic observations of nearby galactic centers

Scientific questions:
- Can a supernova shell deliver matter in the immediate vicinity of a SMBH?
- What are the main parameters influencing the evolution of shells in galactic nuclei?
- Do nuclear starburst events have a net positive or negative impact on the growth of SMBH? Of which magnitude?
- Are the answers to these questions depending on which galactic center is considered?

- Palouš, J.; Ehlerová, S.; Wünsch, R.; Morris, M. R.;
Astronomy & Astrophysics, Volume 644;
Can supernova shells feed supermassive black holes in galactic nuclei?
- Barna, B.; Palouš, J.; Ehlerová, S.; Wünsch, R.; Morris, M. R.; Vermot, P.;
Monthly Notices of the Royal Astronomical Society, Volume 510;
FLASH-light on the RING: hydrodynamic simulations of expanding supernova shells near supermassive black holes
 - Ehlerová, S.; Palouš, J.; Morris, M. R.; Wünsch, R.; Barna, B.; Vermot, P.;
Astronomy & Astrophysics, Volume 668;
How to create Sgr A East. Where did the supernova explode?

Credit for the image: Judy Schmidt @SpaceGeck that we congratulate for her wonderful job