Pavel Kroupa: Moovies
For research on simulating the formation and evolution of galaxies in
Milgromian dynamics, we first needed to develop the code Phantom of
Ramses ( Lueghausen et al. 2015 ). This
MOVIE shows the dynamical evolution of a Milky-Way-type
galaxy which is composed only of stellar particles. Note the buckling
and the development of the bar instability and an X-feature in the
inner region with radius near 2 kpc in the edge-on view.
For research on the formation and evolution of star clusters in
Newtonian dynamics, we mostly use the Aarseth suite of Nbody5-7
programmes ( Aarseth Nody codes ).
Ejections of massive stars from young star clusters:
These two MOVIES show the dynamical evolution of a
30000 Msun (left) and a 3000 Msun (right) very young cluster. The
detailed realistic initial conditions are described in
Oh et al. (2015) and
Oh & Kroupa (2016) . The clusters are initially
mass-segregated, and every star is in a binary. The stars and binaries
follow realistic distribution functions. Note how incredibly
dynamically active the clusters are, shooting out their massive stars
at a high rate and with different velocities, and also with high-order
multiplicities. Note also the nice example of the two-step ejection
( Pflamm-Altenburg & Kroupa 2010 )
which occurs at 5.6 Myr in the right movie: a massive star binary is
expelled and propagates to the right of the cluster, the stars evolve
and when the final supernova occurs the two neutron stars are left
moving on their near-tangential orbital motion such that the neutron
star moving to the left passes the cluster on a trajectory which an
observer would not trace back to the cluster.
Multiple populations of young stars in the Orion Nebula Cluster (ONC):
The big surprise was the report by Beccari et al. (2017) that the ONC has three
populations of very young stars within it, each separated in age by about
0.5-1Myr. This seems to shatter the notion that such clusters form
monolithically within a few hundred thousand years followed by the
expulsion of the majority of mass in the form of ionised gas (
Kroupa, Aarseth & Hurley 2001 ).
But if the massive (ionising) stars form in compact multiple systems near
the centre of a freshly formed population then they can eject each
other dynamically from the cluster, allowing the inflowing gas to
recombine and form the next population of stars. This scenario implies
a narrow mass range for clusters where this process of "repeated
stellar-dynamical termination of feedback-halted filament-accretion
model" may operate and
has been published by Kroupa, Jerabkova, Dinbier et al. (2018). Our N-body
simulations confirm that complete ejections of all ionising stars is
likely if these form at the centre of their embedded cluster and in a
very compact non-hierarchical multiple system ( Wang, Kroupa & Jerabkova 2019 ). This MOVIE
visualises the process of repeated ejections.
The initial dynamical evolution of a small cluster of binary stars
(Heidelberg, March 2000):
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- Aarseth's Nbody6 with modifications (
Kroupa, Aarseth & Hurley 2001).
- Standard local Galactic tidal field;
Plummer density profile, Rhalf=0.2pc, virial equilibrium;
Stellar masses: 0.01-50Msol from KTG93 IMF;
40 binaries: Companion masses paired randomly;
Taurus-Auriga-like period distribution (Kroupa'95);
Latest stellar evolution (Hurley et al. 2000).
- The movie exemplifies dynamical processes that are
important for young clusters.
Stellar masses: Magenta: BDs (0.01-0.08Msol);
Red: M dwarfs (0.08-0.5Msol);
Green: "K" dwarfs (0.5-1Msol);
Blue: massive stars (>1Msol).
Cluster evolution begins with the two most massive
stars sinking to the cluster core within one
crossing time, and forming a binary, after ejecting
it's original companions as well as other low-mass
members. It recoils after a very fast (barely
visible) ejection of an original Mdwarf companion to
the upper left. This hardens the massive binary.
The cluster gains momentum and moves slowly towards
the lower right. Further ejection events, mostly
from the tight central binary, remove further stars
from the cluster.
Observe the fast development of mass segregation,
taking note of the distribution of BDs, and note
how the dynamical evolution time-scale slows as the
cluster expands and looses stars.