This paper addresses the questions of what we have learned about how and when dense star clusters form, and what studies of star clusters have revealed about galaxy formation and evolution. One important observation is that globular clusters are observed to form in galaxy mergers and starbursts in the local universe, which both provides constraints on models of globular cluster formation, and suggests that similar physical conditions existed when most early-type galaxies and their globular clusters formed in the past. A second important observation is that globular cluster systems typically have bimodal color distributions. This was predicted by merger models, and indicates an episodic formation history for elliptical galaxies. A third and very recent result is the discovery of large populations of intermediate age globular clusters in several elliptical galaxies through the use of optical to near-infrared colors. These provide an important link between young cluster systems observed in starbursts and mergers and old cluster systems. This continuum of ages of the metal-rich globular cluster systems also indicates that there is no special age or epoch for the formation of the metal-rich globular clusters, which comprise about half of the cluster population. The paper concludes with a brief discussion of recent results on the globular cluster – low-mass X-ray binary connection.

We present results of N-body simulations on the formation of massive black holes by run-away merging in young star clusters and the later dynamical evolution of star clusters containing massive black holes. We determine the initial conditions necessary for run-away merging to form a massive black hole and study the equilibrium profile that is established in the cluster center as a result of the interaction of stars with the central black hole. Our results show that star clusters which contain black holes have projected luminosity profiles that can be fitted by standard King models. The presence of massive black holes in (post-)core collapse clusters is therefore ruled out by our simulations.

I argue that the widely adopted framework of stellar dynamics survived since 1940s, is not fitting the current knowledge on non-linear systems. Borrowed from plasma physics when several fundamental features of perturbed non-linear systems were unknown, that framework ignores the difference in the role of perturbations in two different classes of systems, in plasma with Debye screening and gravitating systems with no screening. Now, when the revolutionary role of chaotic effects is revealed even in planetary dynamics i.e. for nearly integrable systems, one would expect that for stellar systems, i.e. non-integrable systems, their role have to be far more crucial. Indeed, ergodic theory tools already enabled to prove that spherical stellar systems are exponentially instable due to N-body interactions, while the two-body encounters, contrary to existing belief, are not the dominating mechanism of their relaxation. Chaotic effects distinguish morphological and other properties of galaxies. Using the Ricci curvature criterion, one can also show that a central massive object (nucleus) makes the N-body gravitating system more instable (chaotic), while systems with double nuclei are even more instable than those with a single one.

Turbulence, self-gravity, and cooling convert most of the interstellar medium into cloudy structures that form stars. Turbulence compresses the gas into clouds directly and it moves pre-existing clouds around passively when there are multiple phases of temperature. Self-gravity also partitions the gas into clouds, forming giant regular complexes in spiral arms and in resonance rings and contributing to the scale-free motions generated by turbulence. Dense clusters form in the most strongly self-gravitating cores of these clouds, often triggered by compression from local stars. Pre-star formation processes inside clusters are not well observed, but the high formation rates and high densities of pre-stellar objects, and their power law mass functions suggest that turbulence, self-gravity, and energy dissipation are involved there too.

The production of “super star clusters” (SSCs; luminous, compact star clusters) seems to be a hallmark of intense star formation, particularly in interacting and star-burst galaxies. Their sizes, luminosities, and mass estimates are entirely consistent with what is expected for young Milky Way-type globular clusters (GCs). SSCs are important because of what they can tell us about GC formation and evolution (e.g., initial characteristics and early survival rates). They are also of prime importance as probes of the formation and (chemical) evolution of their host galaxies, and of the initial mass function in the extreme environments required for cluster formation. Recent evidence lends support to the scenario that Milky Way-type GCs (although more metal rich), which were once thought to be the oldest building blocks of galaxies, are still forming today.

Star cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent starbursts. Young clusters are observed to form in a variety of such galaxies, a substantial number resembling the progenitors of globular clusters in mass and size, but with significantly enhanced metallicity. From studies of the metal-poor and metal-rich star cluster populations of galaxies, we can therefore learn about the violent star formation history of these galaxies, and eventually about galaxy formation and evolution. We present a new set of evolutionary synthesis models of our GALEV code, with special emphasis on the gaseous emission of presently forming star clusters, and a new tool to compare extensive model grids with multi-color broad-band observations to determine individual cluster masses, metallicities, ages and extinction values independently. First results for young star clusters in the dwarf starburst galaxy NGC 1569 are presented. The mass distributions determined for the young clusters give valuable input to dynamical star cluster system evolution models, regarding survival and destruction of clusters. We plan to investigate an age sequence of galaxy mergers to see dynamical destruction effects in process.

A new scenario is proposed, in which the continuous creation of stars results into a highly concentrated massive (globular cluster-like) stellar system. We assume that the collapse of a massive cloud leads to the formation of first stars. Their winds and terminal supernova explosions create a standing, small radius, cold and dense shell, where the next stars form. The shell is in steady state location, which is due to a detailed balance established between the ram pressure from the collapsing cloud, the gravitational force exerted on the shell and the ram pressure of the stellar wind from the forming cluster. In this contribution we show that the standing shell remains stable against Rayleigh -Taylor instability, and discuss future prospects of this work.

The youngest super star clusters (SSCs) in the merging Antennae Galaxies (NGC 4038/39) drive supersonic mass-loaded outflows from the HII regions in which they are embedded. High-resolution K-band Keck/NIRSPEC spectroscopy reveals broad, spatially extended Brγ emission in 16 targets. Simple wind models for the line profiles provide good fits and imply cluster mass-loss rates of up to 1.5 M⊙/year and terminal velocities of up to 205 km s−1. The emission-line clusters (ELCs) that drive these outflows constitute at least 15% of the star formation rate in the Antennae, and their high star formation efficiencies imply that they will probably evolve into bound SSCs. The youngest ELC outflows, which are driven primarily by stellar winds, very efficiently entrain ambient matter. The cluster winds transfer or dissipate a large fraction of their energy and momentum in a hot or cool medium that does not emit Brγ. ELCs are the individual engines that power galactic-scale superwinds, viewed in their earliest evolutionary stage.

With the resounding success of Helioseismology in determining the interior structure and rotation of the Sun, and in providing unprecedented studies of the interaction of pulsation and magnetic fields in the solar atmosphere, astronomers have been delighted, after decades of disappointing attempts, with the recent discovery of solar-like oscillations in ξHya, β Hyi, αCen, η Boo and νInd. There is now true seismology of a variety of solar-like stars. Asteroseismology also studies stars with a wide variety of interior and surface conditions. For two decades asteroseismic techniques have been applied to many pulsating stars across the HR Diagram. This review describes for non-specialists pulsation modes in stars and discusses a selection of some of the successes already accomplished in asteroseismology.

The physics of solar and stellar oscillations determine their observable characteristics. I provide a brief overview of the properties of solar-like oscillations, excited by stochastic processes, in other stars. In addition, I consider the current state of investigations of such oscillations, as well as the prospects for an improved understanding of their physics and the properties of the pulsating stars.

Experience in helioseismology provides guidance for modeling challenges in asteroseismology. It guides choices of targets and conditions of observation. The main objectives are the interplay between rotation and convection and the knowledge of the internal magnetic field. Progress on the structure of the outer layers is crucial to avoid mode identification problems.

The solar-like oscillations are oscillations that are expected to be excited by near-surface convection. Apart from the Sun itself, we now have a number of stars where p-mode solar-like oscillations have been detected. In this paper we present a short presentation of those recently discovered oscillations.

P-mode oscillations in the Sun and stars are excited stochasticly by Reynolds stress and entropy fluctuations produced by convection in their outer envelopes. The excitation increases with increasing effective temperature (until envelope convection ceases in the F stars) and also increases with decreasing gravity.

Over the past couple of decades increasingly sophisticated analysis algorithms have been developed in helioseismology. Here I will describe some of these with an emphasis on those most relevant to asteroseismology and some of the lessons learned. I will also discuss some of the properties of stellar oscillations and how those affect the analysis.

Ever since the discovery of the low-degree p modes was announced by Claverie et al. (1979), full-disc helioseismology – seismology of the Sun based on the study of sunlight integrated across the entire disc – has contributed very significantly to our understanding of the deep solar interior and the origin and nature of the oscillation modes which probe it. This paper touches on the principal observational techniques used for full-disc helioseismology and outlines key results and their implications.

Helioseismologists have been highly successful in revealing how the solar interior differentially rotates, through observations of rotationally split eigen p modes of the Sun. What we currently know about the internal rotation of the Sun is reviewed, and outstanding issues are discussed.

The three major local helioseismology methods of time-distance, ring diagrams, and acoustic holography are briefly summarized along with their advantages and disadvantages. Useful tests with artificial data are outlined, and current data comparisons briefly described.

We report new measurements of the sun’s global meridional circulation within the near-surface shear layer for the years 1996 to 2003. The flows are obtained using the local helioseismic technique of ring analysis applied to MDI Dynamics Program data. The most recent estimates of the solar p-angle correction to this data have been incorporated. Previously published accounts that the solar meridional circulation possesses multiple cells within the northern hemisphere (Haber et al. 2002) are not contradicted by the new findings. We do find, however, that with the inclusion of the p-angle correction, cross-equator flows have been eliminated.

Immediate subsurface local solar structures – flow, magnetic, and thermal – especially those associated with active regions, are of considerable interest, and are potentially accessible using high ℓ helioseismology. In recent years, classical modal seismology has been supplemented with new approaches, such as time-distance helioseismology, Hankel analysis, and acoustic holography. Results from time-distance helioseismology on shallow subsurface wave speed are at odds with those from the other methods. A simple model is presented which yields good agreement with the observed Hankel phase shifts of p modes passing through sunspots.