The present-day Earth with its innumerable life forms is a product of cosmic evolution starting with the formation of our galaxy and the dense gas clouds within it, and proceeding through the contraction of one of those clouds about 4.6 Gyr ago, first into filaments and then one or more protostellar disks, planets, and central stars, one of which was our Sun. Radioactive debris from a massive nearby star was included. The planets themselves formed through coagulation, accretion, and fragmentation of solid bodies. Habitability depends on a delicate balance between disk accretion by gravity and dispersal by the central star, which determine the size of the planet and its gaseous envelope, combined with a long period of stellar radiation, which has to disperse this envelope but leave a hospitable secondary atmosphere. The final step toward life involves even more complexity as self-replicating bio-molecules form with ever increasing stability.

Star formation started as a cosmic process soon after the big bang and still continues in the Milky Way, although at a decreasing rate. The formation of dense interstellar clouds, their fragmentation and eventual collapse lead to the birth of stars. The nearby clouds provide the highest resolution for the study of this process. The progress is closely following the improvement of the infrared and radio-wavelength facilities that enables us to follow even the earliest stages of the star-formation process inside molecular clouds. On the other hand, modern numerical simulations can take into account most of the relevant physics and often provide a more direct access into the general principles of star formation. The comparison of observations and simulations is therefore essential. In this paper, will discuss star formation in the solar neighbourhood, concentrating on the prestellar phases leading up to the formation of protostars.

The discovery of the ubiquity of filaments in the interstellar medium in the last two decades has begged the question: “What role do filaments play in star formation?” Here we describe how our automated filament finding algorithms can combine with both magnetic field measurements and high-resolution observations of dense cores in these filaments, to provide a statistically large sample to investigate the effect of filaments on star formation. We find that filaments are likely actively accreting mass from the interstellar medium, explaining why some 60% of stars, and all massive stars, form “on-filament”.

The giant molecular cloud Orion A is the closest massive star-forming region to earth (d ∼ 400 pc). It contains the rich Orion Nebula Cluster (ONC) in the North, and low-mass star-forming regions (L1641, L1647) to the South. To get a better understanding of the differences in star formation activity, we perform an analysis of the gas mass distribution and star formation rate across the cloud. We find that the gas is roughly uniformly distributed, while, oddly, the ONC region produced about a factor of ten more stars compared to the rest of the cloud. For a better interpretation of this phenomenon, we use Gaia DR2 parallaxes, to analyse distances of young stellar objects, using them as proxy for cloud distances. We find that the ONC region indeed lies at about 400 pc while the low-mass star-forming parts are inclined about 70∘ from the plane of the sky reaching until ∼470 pc. With this we estimate that Orion A is an about 90 pc long filamentary cloud (about twice as long as previously assumed), with its “Head” (the ONC region) being “bent” and oriented towards the galactic mid-plane. This striking new view allows us to perform a more robust analysis of this important star-forming region in the future.

Star formation takes place in the dense gas phase, and therefore a simple dense gas and star formation rate relation has been proposed. With the advent of multi-beam receivers, new observations show that the deviation from linear relations is possible. In addition, different dense gas tracers might also change significantly the measurement of dense gas mass and subsequently the relation between star formation rate and dense gas mass. We report the preliminary results the DEnse GAs in MAssive star-forming regions in the Milky Way (DEGAMA) survey that observed the dense gas toward a suite of well-characterized massive star-forming regions in the Milky Way. Using the resulting maps of HCO+ 1–0, HCN 1–0, CS 2–1, we discuss the current understanding of the dense gas phase where star formation takes place.

We use Gaia (DR1, DR2) stellar proper motions to study the kinematics of OB-associations. The average one-dimensional velocity dispersion inside 18 OB-associations with more than 10 Gaia DR1 stars is σv = 3.9 km s−1. The median virial and stellar masses of OB-associations are equal to 7×105 and 9 × 103 solar masses, respectively. The median star-formation efficiency is ε = 2.1%. We have found the expansion in several OB-associations. Models of the Galaxy with a two-component outer ring R1R2 can reproduce the average residual velocities of OB-associations in the Perseus, Sagittarius and Local System complexes.

Star formation is inefficient. Recent advances in numerical simulations and theoretical models of molecular clouds show that the combined effects of interstellar turbulence, magnetic fields and stellar feedback can explain the low efficiency of star formation. The star formation rate is highly sensitive to the driving mode of the turbulence. Solenoidal driving may be more important in the Central Molecular Zone, compared to more compressive driving agents in spiral-am clouds. Both theoretical and observational efforts are underway to determine the dominant driving mode of turbulence in different Galactic environments. New observations with ALMA, combined with other instruments such as CARMA, JCMT and the SMA begin to reveal the magnetic field structure of dense cores and protostellar disks, showing highly complex field geometries with ordered and turbulent field components. Such complex magnetic fields can give rise to a range of stellar masses and jet/outflow efficiencies in dense cores and protostellar accretion disks.

The connection between low- and high-mass filaments is a matter of strong debate. In order to bridge these two filamentary regimes, we have investigated the internal structure of the Integral Filament in Orion using ALMA observations of the N2H+ (1-0) emission line in Band 3 in combination with previous single-dish data. Our ALMA mosaics, the largest of its kind carried out so-far in local clouds, reveal the presence of multiple sonic-like fibers inside this massive filament. In combination with the identification of fibers in regions such as Taurus, Musca, and Perseus, the first unambiguous detection of fibers in Orion highlights the importance of these gas substructures as the fundamental building blocks of both low- and high-mass filaments.

Stars are embedded in different environments of Giant Molecular Clouds during their formation phase. Despite this fact, it is common practice to assume an isolated spherical core as the initial condition for models of individual star formation. To avoid the uncertainties of initial and boundary conditions, we use an alternative approach of zoom-in simulations to account for the environment in which protostars form. Our models show that injections of 26Al from a close-by supernova into the young solar system were highly unlikely. Moreover, we find that the accretion process of protostars is heterogeneous and environment-dependent.

Star formation is spatially clustered across a range of environments, from dense stellar clusters to unbound associations. As a result, radiative or dynamical interactions with neighbouring stars disrupt (proto)planetary systems and limit their radii, leaving a lasting impact on their potential habitability. In the solar neighbourhood, we find that the vast majority of stars form in unbound associations, such that the interaction of (proto)planetary systems with neighbouring stars is limited to the densest sub-regions. However, the fraction of star formation occurring in compact clusters was considerably higher in the past, peaking at ∼50% in the young Milky Way at redshift z ∼ 2. These results demonstrate that the large-scale star formation environment affects the demographics of planetary systems and the occupation of the habitable zone. We show that planet formation is governed by multi-scale physics, in which Mpc-scale events such as galaxy mergers affect the AU-scale properties of (proto)planetary systems.

Low-mass stars form from the gravitational collapse of dense molecular cloud cores. While a general consensus picture of this collapse process has emerged, many details on how mass is transferred from cores to stars remain poorly understood. MASSES (Mass Assembly of Stellar Systems and their Evolution with the SMA), an SMA large project, has just finished surveying all 74 Class 0 and Class I protostars in the nearby Perseus molecular cloud to reveal the interplay between fragmentation, angular momentum, and outflows in regulating accretion and setting the final masses of stars. Scientific highlights are presented in this proceedings, covering the topics of episodic accretion, hierarchical thermal Jeans fragmentation, angular momentum transfer, envelope grain sizes, and disk evolution.

The relative abundances of the radionuclides in the solar system at the time of its birth are crucial arbiters for competing hypotheses regarding the birth environment of the Sun. The presence of short-lived radionuclides, as evidenced by their decay products in meteorites, has been used to suggest that particular, sometimes exotic, stellar sources were proximal to the Sun’s birth environment. The recent confirmation of neutron star - neutron star (NS-NS) mergers and associated kilonovae as potentially dominant sources of r-process nuclides can be tested in the case of the solar birth environment using the relative abundances of the longer-lived nuclides. Critical analysis of the 15 radionuclides and their stable partners for which abundances and production ratios are well known suggests that the Sun formed in a typical massive star-forming region (SFR). The apparent overabundances of short-lived radionuclides (e.g. 26Al, 41Ca, 36Cl) in the early solar system appears to be an artifact of a heretofore under-appreciation for the important influences of enrichment by Wolf-Rayet winds in SFRs. The long-lived nuclides (e.g. 238U, 244Pu, 247Cr, 129I) are consistent with an average time interval between production events of 108 years, seemingly too short to be the products of NS-NS mergers alone. The relative abundances of all of these nuclides can be explained by their mean decay lifetimes and an average residence time in the ISM of ∼200 Myr. This residence time evidenced by the radionuclides is consistent with the average lifetime of dust in the ISM and the timescale for converting molecular cloud mass to stars.

A constraint on Solar System formation is the high 26Al/27Al abundance ratio, 17 times higher than the average Galactic ratio, while the 60Fe/56Fe value was lower than the Galactic value. This challenges the assumption that a nearby supernova was responsible for the injection of these short-lived radionuclides into the early Solar System. We suggest that the Solar System was formed by triggered star formation at the edge of a Wolf-Rayet (W-R) bubble. We discuss the details of various processes within the model using numerical simulations, and analytic and semi-analytic calculations, and conclude that it is a viable model that can explain the initial abundances of 26Al and 60Fe. We estimate that 1%-16% of all Sun-like stars could have formed in such a setting.

Meteoritic evidence shows that the Solar system at birth contained significant quantities of short-lived radioisotopes (SLRs) such as 60Fe and 26Al produced in supernova explosions and in the Wolf-Rayet winds. Explaining how they travelled from these origin sites to the primitive Solar system before decaying is an outstanding problem. In this paper, we present a chemo-hydrodynamical simulation of the entire Milky Way to measure for the distribution of 60Fe/56Fe and 26Al/27Al ratios over all stars in the Galaxy. We show that the Solar abundance ratios are well within the normal range. We find that SLRs are abundant in newborn stars because star formation is correlated on Galactic scales, so that ejecta preferentially enrich atomic gas that will subsequently be accreted onto existing GMCs or will form new ones. Thus new generations of stars preferentially form in patches of the Galaxy contaminated by previous generations of stellar feedback.

The earliest phases of star formation are characterised by intense mass accretion from the circumstellar disk to the central star. One group of young stellar objects, the FU Orionis-type stars exhibit accretion rate peaks accompanied by bright eruptions. The occurance of these outbursts might solve the luminosity problem of protostars, play a key role in accumulating the final star mass, and have a significant effect on the parameters of the envelope and the disk. In the framework of the Structured Accretion Disks ERC project, we are conducting a systematic investigation of these sources with millimeter interferometry to examine whether they represent normal young stars in exceptional times or they are unusual objects. Our results show that FU Orionis-type stars can be similar to both Class I and Class II systems and may be in a special evolutionary phase between the two classes with their infall-driven episodic eruptions being the main driving force of the transition.

I present our observations and modeling of the 1.3 mm and 3.18 mm dust continuum emission in Class 0 protostars, from the IRAM-PdBI CALYPSO survey. We show that most protostars are better reproduced by models including a disk-like dust continuum component contributing to the flux at small scales, but less than 25% of these candidate protostellar disks are resolved at radii >60 au, which favors magnetized models of rotating protostellar collapse for disk formation (Maury et al. 2019). I also present new ALMA observations of the molecular line emission in the IRAM04191 protostar, suggesting a small counter-rotating disk is detected in this young low-luminosity solar-type protostar. Finally, I show our ALMA observations of the magnetic field topology in the B335 protostar, which when compared to the typical output from protostellar collapse models, suggest the magnetic field might be responsible for constraining the disk size to remain very small in this protostar (Maury et al. 2018).

Planet formation takes place in the gaseous and dusty disks that surround young stars, known as protoplanetary disks. With the advent of sensitive observations and together with developments in theory, our field is making rapid progress in understanding how the evolution of protoplanetary disks takes place, from its inception to the end result of a fully-formed planetary system. In this review, I discuss how observations that trace both the dust and gas components of these systems inform us about their evolution, mass budget, and chemistry. Particularly, the process of disk evolution and planet formation will leave an imprint on the distribution of solid particles at different locations in a protoplanetary disk, and I focus on recent observational results at high angular resolution in the sub-millimeter regime, which have revealed a variety of substructures present in these objects.

The gas dynamics of protoplanetary disks (PPDs) plays a crucial role in almost all stages of planet formation, yet it is far from being well understood largely due to the complex interplay among various microphysical processes. Primarily, PPD gas dynamics is likely governed by magnetic fields, and their coupling with the weakly ionized gas is described by non-ideal magnetohydrodynamic (MHD) effects. Incorporating these effects, I will present the first fully global simulations of PPDs that include the most realistic disk microphysics. Accretion and disk evolution is primarily driven by magnetized disk winds with significant mass loss comparable to accretion rate. The overall disk gas dynamics strongly depends on the polarity of large-scale poloidal magnetic field threading the disk owing to the Hall effect. The flow structure in the disk is highly unconventional with major implications on planet formation.

Disks around young stars are the sites of planet formation. As such, the physical and chemical structure of disks have a direct impact on the formation of planetary bodies. Outflowing winds remove angular momentum and mass and affect the disk structure and therefore potentially planet formation. Until very recently, we have lacked the facilities to provide the necessary observational tools to peer into the wind launching and planet forming regions of the young disks. Within the framework of the Resolving star formation with ALMA program, young protostellar systems are targeted with ALMA to resolve the disk formation, outflow launching and planet formation. This contribution presents the first results of the program. The first resolved images of outflow launching from a disk were recently reported towards the Class I source TMC1A (Bjerkeli et al. 2016) where we also present early evidence of grain growth (Harsono et al. 2018).

Young low-mass protostellar sources are known to show significant chemical diversity in their envelopes at a few 1000s au scale; two distinct cases are hot corino chemistry and warm carbon-chain chemistry (WCCC). It is of great interest how the chemical diversity is inherited to chemistry of disk-forming regions. With the recent ALMA observations, we found that the chemical diversity in envelopes is indeed delivered into the disk-forming regions at a 100 au scale. Moreover, the chemical composition changes drastically from envelopes to disks. We also found sources with the hybrid chemical characteristics; both hot corino chemistry and WCCC occur in spatially separated parts of a single source. This hybrid case may be a common occurrence, while hot corinos and WCCC sources are regarded as distinct cases. This unified view of chemistry in disk-forming regions will be an important clue to tracing the chemical evolution from protostellar cores to protoplanetary disks.