Cologne-Prague-Kiel meeting 2016 (CPK16):
Star formation, accretion, and feedback in galactic nuclei

Scientific rationale

A recent detection of gravitational waves by LIGO collaboration has strengthened the role of general relativity in understanding the evolution and properties of black holes. Of special importance is the supermassive black hole associated with the compact radio source Sgr A* at the center of the Milky Way. General relativity has been needed to study the effects on event horizon scales as well as post-newtonian effects on stellar orbits in the Galactic center.

The informal Cologne-Prague-Kiel meeting will bring together junior as well as senior researchers from Cologne, Prague and Kiel research institutes to exchange their theoretical and observational skills concerning the black hole physics. The meeting will consist of a series of lectures and individual discussions.

The meeting builds on the tradition of previous Cologne-Prague-Kiel meetings: CPK13 , CPK15 and CPP15 .


It appears that star formation, accretion, and feedback are closely coupled in galactic nuclei. Especially in the Galactic centre, there is an evidence of the recent formation of massice stars via the gravitational instability of a massive accretion disc (Levin & Beloborodov 2003). This star-formation event occured several million years ago. It also probably led to an enhanced accretion state of Sgr A*, which may be linked to outflows that formed Fermi bubbles observed in X-ray and Gamma-ray domains.

Recent discovery of several near-infrared excess sources, among which the Dusty S-cluster Object (DSO/G2) is the most monitored, raised a question of even more recent star formation event very close to the central black hole (several hundred thousand years ago). Jalali et al. from the University of Cologne found out that such objects may be formed in radially infalling molecular clumps, whose source is the circumnuclear disc. The process of transporting molecular gas from larges scales to galactic nuclei is observed in nearby QSOs, where molecular circumnuclear structures have been found. There is also an evidence of ongoing star formation in these molecular rings (Busch et al.).


The meeting starts on November 30 (Wednesday) and ends on December 2, 2016 (Friday).

Final report and summary of the meeting

Molecular clouds in the vicinity of Sgr A* (Lydia Moser), mid-infrared observations of the Galactic centre, as well as L-band detection of faint sources in the Galactic centre (Nadeen Sabha, Elaheh Hosseini) allow us to study the gas, dust and stellar content of the central parsec. Stars and gas interact with each other and lead to bow shock sources (Lýdia Štofanová, Nadeen Sabha). Hence, these observations and the interpretation of the corresponding results allow us to map out the

Conditions of star formation in the central parsec.

In fact, more than two thirds of the contributions that covered the topic are directly or indirectly linked to this CRC956 topic. Among the dusty sources (possibly young stars) in the central region is the Dusty S-cluster Object (DSO/G2). The properties of the DSO and other NIR-excess sources were summarized (Florian Peissker, Mónica Valencia-S). NIR polarimetry observations of the Galactic centre (Sgr A* and DSO) give information on the stability of the accretion phenomenon at the Galactic Center. Combined with the models polarimetry data constrain the nature of the DSO (Banafsheh Shahzamanian, Michal Zajaček).

The central parsec contains also the SMBH Sgr A* that is a combined source of wind and a sink for a central accretion process. Its activities can be traced in the radio domain (Abhijeet Borkar) where it gives rise to weak (Lukas Steiniger,) and strong flare emission (Matthias Subroweit) that can partly also be observed in the X-ray domain (Enmanuelle Mossoux). Through accretion and feedback the central object needs to be considered in discussing the conditions of star-formation in the central parsec of the Milky Way. The mass of Sgr A* as well as the dynamic history or stars in the central arcsecond can be traced by the S-stars (Marzieh Parsa). The mass can alternatively be derived by the shape of the bright X-ray flares (Grischa Karssen).

Accretion of matter towards the central regions of galaxies results in the formation of stars as well as – most likely at the same time and coupled to it – the formation of SMBHs. How the SMBH Sgr A* may have formed as a part of an ensamble of compact masses (Lars Bösch) and how exotic it is was pointed out (Wolfgang Duschl). The accretion process towards compact objects like a Sgr A* may possibly work in the form of a slowly rotating transonic accretion flows with shocks (Petra Suková).

In extragalactic sources star formation, accretion, and feedback are known to be closely linked. Jets like the one in M87 provide feedback of the accretion into the surrounding ISM. How the jet in M87 may be described was shown as an application of the MAGSPOT code (Madalina Badea). Accretion and star formation in the nuclei of extragalactic sources can be studied through multiwavelength programs carried out on nearby AGN and quasars (Gerold Busch). A detailed example covers the nuclear interstellar medium of NGC1365 (Nastaran Fazeli). The interaction of the nuclear emission (e.g. of Seyfert 1 galaxies) with the surrounding ISM can be studied through X-ray spectroscopy of polar-scattered nuclei (Romana Mikušincová).

Elements of Black Hole Astrophysics in the Era of New Instruments were introduced (Vladimir Karas). Recent mm-VLBI results allow to observe the accretion activity with the highest angular resolution (Andreas Eckart). Here observations with the EHT in the radio and GRAVITY in the infrared are most promising. The mid-infrared properties of the stars, dust and gas as well as the non-thermal source Sgr A* will be observed in the near future with the JWST (Steffen Rost, Sebastian Vider).

Meeting photos

Press coverage


Organizer: I.Physikalisches Institut, Universität zu Köln

Scientific participants:

Scientific and local organizing committee:

Andreas Eckart (chair of LOC) University of Cologne/MPIfR
Vladimír Karas Astronomical Institute of the Academy of Sciences, Prague/Charles University in Prague
Wolfgang Duschl University of Kiel
Silke Britzen Max Planck Institute for Radioastronomy, Bonn
Ondrej Kopáček Astronomical Institute of the Academy of Sciences, Prague
Michal Zajaček (LOC, website) University of Cologne/MPIfR (former: Charles University in Prague)
Gerold Busch (LOC) University of Cologne
Monica Valencia-S. (LOC) University of Cologne


Castle Wahn , University of Cologne, Burgallee 2, 51127 Köln

Castle Wahn Tour (in German)

Scientific topics

Astronomy picture of the day
Astronomy Picture of the Day

Participants and Program (final)

Confirmed speakers

# Name Institute Contribution
1 Lydia Moser Ph1 Uni Koeln/AIfA/German ARC node Molecular clouds in the vicinity of Sgr A*
2 Matthias Subroweit Ph1 Uni Koeln Sub-mm to X-ray properties of Sgr A*
3 Nastaran Fazeli Ph1 Uni Koeln Nuclear interstellar medium of NGC1365
4 Enmanuelle Mossoux Ph1 Uni Koeln/University of Strasbourg Multiwavelength study of the flaring activity of Sagittarius A* in 2014 February-April
5 Florian Peissker Ph1 Uni Koeln K-band continuum of the Dusty S-cluster Object (DSO/G2)
6 Banafsheh Shahzamanian Ph1 Uni Koeln Polarized emission of Sgr A* and the DSO
7 Lukas Steiniger Ph1 Uni Koeln Weak NIR/radio flare emission of Sgr A*
8 Mónica Valencia-S. Ph1 Uni Koeln Line emission of the DSO
9 Nadeen Sabha Ph1 Uni Koeln Mid-infrared observations of the Galactic centre
10 Seyedeh Elaheh Hosseini Ph1 Uni Koeln/MPIfR L-band detection of faint sources in the Galactic centre
11 Andreas Eckart Ph1 Uni Koeln/MPIfR Recent mm-VLBI results
12 Marzieh Parsa Ph1 Uni Koeln/MPIfR Stellar orbits near Sgr A*
13 Gerold Busch Ph1 Uni Koeln Low-mass black holes in galactic nuclei
14 Matthew Horrobin Ph1 Uni Koeln GRAVITY
15 Madalina Badea Ph1 Uni Koeln M87 and the application of the MAGSPOT code
16 Grischa Karssen Ph1 Uni Koeln Black hole mass determination using bright X-ray flares
17 Michal Zajaček Ph1 Uni Koeln/MPIfR What is the nature of near-infrared excess sources in the Galactic centre?
18 Steffen Rost Ph1 Uni Koeln Upcoming observations with JWST
19 Sebastian Vider Ph1 Uni Koeln Upcoming observations with JWST
20 Vladimír Karas Astronomical Institute of the Czech Academy of Sciences Elements of Black Hole Astrophysics in the Era of New Instruments
21 Lýdia Štofanová Charles University in Prague Bow shocks in the Galactic centre
22 Romana Mikušincová Charles University in Prague X-ray spectroscopy of polar-scattered Seyfert 1 galaxies
23 Abhijeet Borkar Astronomical Institute of the Czech Academy of Sciences/Ph1 Uni Koeln Millimeter radio interferometry from Sgr A* and its surroundings
24 Petra Suková Center for Theoretical Physics of the Polish Academy of Sciences/Astronomical Institute of the Czech Academy of Sciences Slowly rotating transonic accretion flows with shocks
25 Wolfgang Duschl University of Kiel How exotic is the (S)MBH in the GC?
26 Lars Bösch University of Kiel Ensemble evolution of supermassive black holes

Download the list of participants: LIST .
Download the Programme of the meeting: Programme .

Social events


The registration of all participants is on Wednesday, November 30, from 9 am -10 am, or individually upon arrival, at Castle Wahn.

The maximum capacity is 25 participants, most of whom will be from Cologne, Kiel, and Prague. In case you are interested in the meeting and would like to attend or give a talk, please contact Michal Zajaček (cc Andreas Eckart) to get information about free capacity.

Background photo: Sagittarius Star Cloud, Credit:The Hubble Heritage Team (AURA/STScI/NASA)
Last change: 26/11/2016 by M. Zajaček (webmaster) .