Young massive star clusters

Young massive clusters are dense aggregates of young stars that form the fundamental building blocks of galaxies. Several examples exist in the Milky Way Galaxy and the Local Group, but they are particularly abundant in starburst and interacting galaxies. The few young massive clusters that are close enough to resolve are of prime interest for studying the stellar mass function and the ecological interplay between stellar evolution and stellar dynamics. The distant unresolved clusters may be effectively used to study the star-cluster mass function, and they provide excellent constraints on the formation mechanisms of young cluster populations. Young massive clusters are expected to be the nurseries for many unusual objects, including a wide range of exotic stars and binaries. So far only a few such objects have been found in young massive clusters, although their older cousins, the globular clusters, are unusually rich in stellar exotica. In this review we focus on star clusters younger than $\sim100$ Myr, more than a few current crossing times old, and more massive than $\sim10^4$ \Msun, irrespective of cluster size or environment. We describe the global properties of the currently known young massive star clusters in the Local Group and beyond, and discuss the state of the art in observations and dynamical modeling of these systems. In order to make this review readable by observers, theorists, and computational astrophysicists, we also review the cross-disciplinary terminology.Comment: Only 88 pages. To be published in ARAA. Final version to be submitted on Friday 12 Februar

Oort cloud Ecology II: Extra-solar Oort clouds and the origin of asteroidal interlopers

We simulate the formation and evolution of Oort clouds around the 200 nearest stars (within 16pc according to the Gaia DR2) database. This study is performed by numerically integrating the planets and minor bodies in orbit around the parent star and in the Galactic potential. The calculations start 1\,Gyr ago and continue for 100Myr into the future. In this time frame, we simulate how asteroids (and planets) are ejected from the star's vicinity and settle in an Oort cloud and how they escape the local stellar gravity to form tidal steams. A fraction of 0.0098 to 0.026 of the asteroids remain bound to their parent star. The orbits of these asteroids isotropizes and circularizes due to the influence of the Galactic tidal field to eventually form an Oort cloud between 10^4 and 2 10^5au. We estimate that 6% of the nearby stars may have a planet in its Oort cloud. The majority of asteroids (and some of the planets) become unbound from the parent star to become free floating in the Galactic potential. These soli lapides remain in a similar orbit around the Galactic center as their host star, forming dense streams of rogue interstellar asteroids and planets. The Solar system occasionally passes through such tidal streams, potentially giving rise to occasional close encounters with object in this stream. The two recently discovered objects, 1I/(2017 Q3) 'Oumuamua and 2I/(2019 Q4) Borisov, may be such objects. Although the direction from which an individual solus lapis originated cannot easily be traced back to the original host, multiple such objects coming from the same source might help to identify their origin. At the moment the Solar system is in the bow or wake of the tidal stream of 10 of the nearby stars which might contribute considerably to the interaction rate. (abridged)Comment: accepted for publication in A&A, see animation https://youtu.be/0fYeAW3e9b

Relativistic Binaries in Globular Clusters

Galactic globular clusters are old, dense star systems typically containing 10\super{4}--10\super{7} stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution that leads to relativistic binaries, and current and possible future observational evidence for this population. Our discussion of globular cluster evolution will focus on the processes that boost the production of hard binary systems and the subsequent interaction of these binaries that can alter the properties of both bodies and can lead to exotic objects. Direct {\it N}-body integrations and Fokker--Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.Comment: 88 pages, 13 figures. Submitted update of Living Reviews articl

Oort cloud Ecology: II. the chronology of the formation of the Oort cloud

Stars and planetary system

Space station user's handbook (Revised)

A modular space station concept that furnishes facilities which may be used for experimentation and application during earth orbit missions is described in a user's handbook. The subjects discussed are: (1) overall profile and mission activities for five year on-orbit program, (2) electromagnetic energy transmission through earth atmosphere, (3) effects of atmosphere in limiting resolution, and (4) the hydrological cycle as these subjects apply to the space station data acquisition function

Space station user's handbook

A user's handbook for the modular space station concept is presented. The document is designed to acquaint science personnel with the overall modular space station program, the general nature and capabilities of the station itself, some of the scientific opportunities presented by the station, the general policy governing its operation, and the relationship between the program and participants from the scientific community

The Second Conference on Lunar Bases and Space Activities of the 21st Century, volume 1

These papers comprise a peer-review selection of presentations by authors from NASA, LPI industry, and academia at the Second Conference (April 1988) on Lunar Bases and Space Activities of the 21st Century, sponsored by the NASA Office of Exploration and the Lunar Planetary Institute. These papers go into more technical depth than did those published from the first NASA-sponsored symposium on the topic, held in 1984. Session topics covered by this volume include (1) design and operation of transportation systems to, in orbit around, and on the Moon, (2) lunar base site selection, (3) design, architecture, construction, and operation of lunar bases and human habitats, and (4) lunar-based scientific research and experimentation in astronomy, exobiology, and lunar geology

NASA thesaurus. Volume 1: Hierarchical Listing

There are over 17,000 postable terms and nearly 4,000 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary and Volume 3 - Definitions

Clues from stellar catastrophes

This thesis uses catastrophic stellar events (supernovae and stellar collisions) to investigate different aspects of their environment. The first part of the thesis examines what happens to supernova remnants near supermassive black holes like the one in the Milky Way Galaxy. To do so, a technique is first developed for predicting the evolution of supernova remnants in non-uniform densities. This is used to demonstrate how supermassive black hole environments determine the evolution and lifetime of supernova remnants. Conversely, observations of supernova remnants can then be used to infer properties of the surroundings of supermassive black holes. Therefore, predictions are then given for the X-ray emission that could be observed from core-collapse supernova remnants in these regions. This emission can compete with other sources, such the accretion flow of the supermassive black hole itself. Next, the problem of a core-collapse supernova in a close binary system is considered, where the effect on the companion is studied to predict the properties of runaway stars from binaries disrupted after a supernova. Finally, simulations of blue stragglers, formed from stellar collisions, are used to learn about the globular clusters containing them. Estimating the collision times reveals details about the evolutionary history of the cluster.Stars and planetary system