Dark Clouds Research Articles

Star cluster progenitors are dynamically decoupled from their parent molecular clouds

ABSTRACT The formation of stellar clusters dictates the pace at which galaxies evolve, and solving the question of their formation will undoubtedly lead to a better understanding of the Universe as a whole. While it is well known that star clusters form within parsec-scale overdensities of interstellar molecular gas called clumps, it is, however, unclear whether these clumps represent the high-density tip of a continuous gaseous flow that gradually leads towards the formation of stars, or a transition within the gas physical properties. Here, we present a unique analysis of a sample of 27 infrared dark clouds embedded within 24 individual molecular clouds that combine a large set of observations, allowing us to compute the mass and velocity dispersion profiles of each, from the scale of tens of parsecs down to the scale of tenths of a parsec. These profiles reveal that the vast majority of the clouds, if not all, are consistent with being self-gravitating on all scales, and that the clumps, on parsec-scale, are often dynamically decoupled from their surrounding molecular clouds, exhibiting steeper density profiles (ρ∝r−2) and flat velocity dispersion profiles (σ∝r0), clearly departing from Larson’s relations. These findings suggest that the formation of star clusters correspond to a transition regime within the properties of the self-gravitating molecular gas. We propose that this transition regime is one that corresponds to the gravitational collapse of parsec-scale clumps within otherwise stable molecular clouds.

Experimental and Theoretical Investigation of the Reaction of NH2 with NO at Very Low Temperatures.

The first experimental study of the low-temperature kinetics of the gas-phase reaction between NH2 and NO has been performed. A pulsed laser photolysis-laser-induced fluorescence technique was used to create and monitor the temporal decay of NH2 in the presence of NO. Measurements were carried out over the temperature range of 24-106 K, with the low temperatures achieved using a pulsed Laval nozzle expansion. The negative temperature dependence of the reaction rate coefficient observed at higher temperatures in the literature continues at these lower temperatures, with the rate coefficient reaching 3.5 × 10-10 cm3 molecule-1 s-1 at T = 26 K. Ab initio calculations of the potential energy surface were combined with rate theory calculations using the MESMER software package in order to calculate and predict rate coefficients and branching ratios over a wide range of temperatures, which are largely consistent with experimentally determined literature values. These theoretical calculations indicate that at the low temperatures investigated for this reaction, only one product channel producing N2 + H2O is important. The rate coefficients determined in this study were used in a gas-phase astrochemical model. Models were run over a range of physical conditions appropriate for cold to warm molecular clouds (10 to 30 K; 104 to 106 cm-3), resulting in only minor changes (<1%) to the abundances of NH2 and NO at steady state. Hence, despite the observed increase in the rate at low temperatures, this mechanism is not a dominant loss mechanism for either NH2 or NO under dark cloud conditions.

Detection and modelling of CH3NC in TMC-1

ABSTRACT Two closely related isomeric pairs of cyanides, CH3[CN/NC] and H2C[CN/NC], are studied in cold, dark interstellar cloud conditions. In contrast to the diverse detections of methyl cyanide (CH3CN) in space, methyl isocyanide (CH3NC) has previously only been observed in warm and hot star-forming regions. We report the detection of CH3NC in the cold pre-stellar core Taurus Molecular Cloud (TMC-1) using the Green Bank Telescope with a detection significance of 13.4σ. Hyperfine transitions in H2CCN and quadrupole interactions in CH3CN and CH3NC were matched to a spectral line survey from the Green Bank Telescope Observations of TMC-1: Hunting for Aromatic Molecules large project on the Green Bank Telescope, resulting in abundances with respect to hydrogen of $1.92^{+0.13}_{-0.07} \times 10^{-9}$ for the cyanomethyl radical (H2CCN), $5.02^{+3.08}_{-2.06} \times 10^{-10}$ for CH3CN, and $2.97^{+2.10}_{-1.37} \times 10^{-11}$ for CH3NC. Efforts to model these molecules with the three-phase gas-grain code nautilus in TMC-1 conditions overproduce both CH3CN and CH3NC, though the ratio of ∼5.9 per cent is consistent across observations and models of these species. This may point to missing destruction routes in the model. The models capture the larger abundance of H2CCN well. Dissociative recombination is found to be the primary production route for these molecules, and reactions with abundant ions are found to be the primary destruction routes. H + CH3NC is investigated with transition state theory as a potential destruction route, but found to be too slow in cold cloud conditions to account for the discrepancy in modelled and observed abundances of CH3NC.

The Infrared Extinction Law in the Ophiuchus Molecular Cloud Based on the UKIDSS and Spitzer c2d Surveys

Investigating the extinction properties in dense molecular clouds is of significant importance for understanding the behavior of interstellar dust and its impact on observations. In this study, we comprehensively examined the extinction law in the Ophiuchus cloud across a wavelength range from 0.8 μm to 8 μm. To achieve this, we analyzed NIR and MIR data obtained from the UKIDSS GCS and the Spitzer c2d survey, respectively. By fitting a series of color–color diagrams, we determined color-excess ratios EJ−λ/EJ−K for seven passbands. These ratios were then directly converted to derive the relative extinction law Aλ/AK. Our findings demonstrate that the Ophiuchus cloud exhibits a characteristic of flat MIR extinction, consistent with previous studies. Additionally, our results reveal variations in the extinction law with extinction depth, indicating a flatter trend from the NIR to MIR bands as extinction increases. Notably, our analysis reveals no significant difference in the MIR extinction law among the four dark clouds: L1712, L1689, L1709, and L1688. However, distinct variations were observed in the extinction law for regions outside the dark clouds, specifically L1688N and L1688W. These regions displayed lower color-excess ratios EJ−λ/EJ−K in the Spitzer/IRAC bands. This observation lends support to the dust growth occurring in the dense regions of the Ophiuchus cloud.

COVID‐19 retreats and world recovers: A silver lining in the dark cloud

AbstractThe coronavirus disease (COVID‐19), which the World Health Organization classified as the Sixth Public Health Emergency Of International Concern (PHEIC) on January 30, 2020, is no longer a PHEIC. Millions were affected due to unawareness. The increase in fatalities and shortage of medicine was the first outrage of COVID‐19. As per the Johns Hopkins COVID‐19 resource center database, it was observed that the disease has spread dynamically across 200+ nations worldwide affecting more than 600 million people from 2019 to 2023, and over thousands of people were victimized regularly at a 2% mortality rate (approx.). In the midway, the mutant variants of concern like omicron, and delta have also created havoc and caused significant impact on public health, global economy, and lifestyle. Since 2019, 3 years now passed and the dynamic disease statistics seem decelerated; moreover, the prevalence of COVID‐19 is also fading. The Johns Hopkins resource center has also stopped recording the data of the global pandemic recently from March 10, 2023. Hence, based on the facts, we are presenting a concise report on the pandemic from 2019 to 2023, which includes a brief discussion of the global pandemic. We have highlighted global epidemiology, emphasizing the Indian COVID scenario, vaccination across the globe, and the psychosocial and geopolitical consequences of COVID‐19 with a brief background to pathology, clinical management, and the worldwide response against triage. A lot has changed and still needs to change after three tough years of COVID‐19. Even though science has progressed and advanced research in medicine is pointing toward future generations, there is no standard care supplied for COVID‐19‐like calamities. COVID‐19 cases might have declined but its influence on the society is still stagnant. This COVID experience has taught us that, despite our bleak beginnings, there is always hope for the future and that we must act with foresight to improve things for future generations.

B-fields and Dust in Interstellar Filaments Using Dust Polarization (BALLAD-POL). I. The Massive Filament G11.11–0.12 Observed by SOFIA/HAWC+

We report the first measurement of polarized thermal dust emission toward the entire infrared dark cloud G11.11−0.12 taken by the polarimeter SOFIA/HAWC+ at 214 μm. The obtained magnetic fields (B-fields) from the polarized emission of the early-stage and massive filament tend to be perpendicular to its spine. We produce a map of B-field strengths for the center region of the filament. The strengths vary in the range of 100–600 μG and are strongest along the filament's spine. The central region is sub-Alfvénic and mostly subcritical, meaning that B-fields dominate over turbulence and are strong enough to resist gravitational collapse. The alignment and properties of dust grains in the filament are studied using radiative torque (RAT) theory. We find the decrease of polarization degree P with emission intensity I, i.e., depolarization effect, of the form P ∝ I −α with α ∼ 0.8–0.9, implying a significant loss of grain alignment in the filament's spine. The depolarization can be explained by the decrease in RAT alignment efficiency toward the denser regions with weaker radiation field, which cannot be explained by B-field tangling. We study the effect of the enhanced magnetic relaxation by embedded iron inclusions on RAT alignment and find that the high polarization fraction P ∼ 20%–30% in the outer layer of the filament is potential evidence for the magnetically enhanced RAT alignment mechanism. This is the first time this effect is evaluated in a filament. Based on the polarization fraction and RAT alignment theory, we also find evidence for grain growth in the filament.

Laboratory and astronomical discovery of the cyanovinyl radical H2CCCN

We report the first laboratory and interstellar detection of the α-cyano vinyl radical (H2CCCN). This species was produced in the laboratory by an electric discharge of a gas mixture of vinyl cyanide, CH2CHCN, and Ne. Its rotational spectrum was characterized using a Balle-Flygare narrowband-type Fourier-transform microwave spectrometer operating in the frequency region of 8–40 GHz. The observed spectrum shows a complex structure due to tunneling splittings between two torsional sublevels of the ground vibronic state, 0+ and 0−, derived from a large-amplitude inversion motion. In addition, the presence of two equivalent hydrogen nuclei makes it necessary to discern between ortho- and para-H2CCCN. A least-squares analysis reproduces the observed transition frequencies with a standard deviation of ca. 3 kHz. Using the laboratory predictions, this radical was detected in the cold dark cloud TMC-1 using the Yebes 40 m telescope and the QUIJOTE1 line survey. The 40, 4-30, 3 and 50, 5-40, 4 rotational transitions, composed of several hyperfine components, were observed in the 31.0–50.4 GHz range. Adopting a rotational temperature of 6 K, we derived a column density of (1.4±0.2)×1011 cm−2 and (1.1±0.2)×1011 cm−2 for ortho-H2CCCN and para-H2CCCN, respectively. The reaction of C + CH3CN emerges as the most likely route to H2CCCN in TMC-1, and possibly that of N + CH2CCH as well.

The role of magnetic fields in the formation of the filamentary infrared dark cloud G11.11–0.12

ABSTRACT We report on the near-infrared polarimetric observations of G11.11–0.12 (hereafter G11) obtained with SIRPOL on the 1.4 m IRSF telescope. The starlight polarisation of the background stars reveals the on-sky component of magnetic fields in G11, and these are consistent with the field orientation observed from polarised dust emission at $850\, \mu$m. The magnetic fields in G11 are perpendicular to the filament, and are independent of the filament’s orientation relative to the Galactic plane. The field strength in the envelope of G11 is in the range $50-100\, \mu$G, derived from two methods. The analyses of the magnetic fields and gas velocity dispersion indicate that the envelope of G11 is supersonic but sub-Alfvénic. The critical mass-to-flux ratio in the envelope of G11 is close to 1 and increases to ≳ 1 on the spine of G11. The relative weights on the importance of magnetic fields, turbulence and gravity indicate that gravity dominates the dynamical state of G11, but with significant contribution from magnetic fields. The field strength, |B|, increases slower than the gas density, n, from the envelope to the spine of G11, characterized by |B|∝n0.3. The observed strength and orientation of magnetic fields in G11 imply that supersonic and sub-Alfvénic gas flow is channelled by the strong magnetic fields and is assembled into filaments perpendicular to the magnetic fields. The formation of low-mass stars is enhanced in the filaments with high column density, in agreement with the excess of low-mass protostars detected in the densest regions of G11.

Updated Inventory of Carbon Monoxide in the Taurus Molecular Cloud

The most extensive survey of carbon monoxide (CO) gas in the Taurus molecular cloud relied on 12CO and 13CO J = 1 → 0 emission only, distinguishing the region where 12CO is detected without 13CO (named mask 1 region) from the one where both are detected (mask 2 region) (Goldsmith et al. ; Pineda et al. ). We have taken advantage of recent 12CO J = 3 → 2 James Clerk Maxwell Telescope observations, where they include mask 1 regions to estimate density, temperature, and N(CO) with a large velocity gradient model. This represents 1395 pixels out of ∼1.2 million in the mark 1 region. Compared to Pineda et al. () results and assuming a T kin of 30 K, we find a higher volume density of molecular hydrogen of 3.3 × 103 cm−3, compared to their 250–700 cm−3, and a CO column density of 5.7 × 1015 cm−2, about a quarter of their value. The differences are important and show the necessity to observe several CO transitions to better describe the intermediate region between the dense cloud and the diffuse atomic medium. Future observations to extend the 12CO J = 3 → 2 mapping further away from the 13CO-detected region comprising mask 1 are needed to revisit our understanding of the diffuse portions of dark clouds.

Branding the nation in the era of climate crisis: Eco‐nationalism and the promotion of green national sovereignty

AbstractThis article examines the contemporary discourse of eco‐nationalism and its promotion of national sovereignty and belonging. I consider some of the strategies, symbols and narratives by which nationalist movements and political leaders have evoked environmental problems and particularly the global threat of climate change to justify excluding populations from ‘native’ lands, erect walls or other physical boundaries around national territories, and limit international traffic of people and goods. This promotion of nation seizes on concerns for continued collective existence, turning away from participation in global networks of culture, capital and cosmopolitanism to act as a bulwark against these networks. As such, it presents a mirror image of global nationalism: whereas the aim is still to take heed of global phenomena, these phenomena now appear as dark clouds on the horizon, from which national citizens must take cover.

Deep search for glycine conformers in Barnard 5

ABSTRACT One of the most fundamental hypotheses in astrochemistry and astrobiology states that crucial biotic molecules like glycine (NH2CH2COOH) found in meteorites and comets are inherited from early phases of star formation. Most observational searches for glycine in the interstellar medium have focused on warm high-mass molecular cloud sources. However, recent studies suggest that it might be appropriate to shift the observational focus to cold low-mass sources. We aim to detect glycine towards the so-called methanol hotspot in the Barnard 5 dark cloud. The hotspot is a cold source (Tgas ≈ 7.5 K) with yet high abundances of complex organic molecules (COMs) and water in the gas phase. We carried out deep pointed observations with the Onsala 20 m telescope, targeting several transitions of glycine conformers I and II (Gly-I and Gly-II) in the frequency range 70.2–77.9 GHz. No glycine lines are detected towards the targeted position, but we use a line stacking procedure to derive sensitive abundance upper limits w.r.t. H2 for Gly-I and Gly-II, i.e. ≤(2–5) × 10−10 and ≤(0.7–3) × 10−11, respectively. The obtained Gly-II upper limits are the most stringent for a cold source, while the Gly-I upper limits are mostly on the same order as previously measured limits. The measured abundances w.r.t. H2 of other COMs at the B5 methanol hotspot range from 2 × 10−10 (acetaldehyde) to 2 × 10−8 (methanol). Hence, based on a total glycine upper limit of (2–5) × 10−10, we cannot rule out that glycine is present but undetected.

The AGN fuelling/feedback cycle in nearby radio galaxies

We present Australia Compact Telescope Array (ATCA) 21 cm observations of the nearby low-excitation radio galaxy (LERG) NGC 3100. This is the brightest galaxy of a loose group and it hosts a young (∼2 Myr) radio source. The ATCA observations reveal for the first time the presence of neutral hydrogen (H I) gas in absorption in the centre of this radio galaxy, and in emission in two low-mass galaxies of the group and in a diffuse dark cloud in the proximity of NGC 3100. The sensitivity to low-column density gas (NHI ∼ 1019 cm−2) allows us to reveal asymmetries in the periphery of most of the H I-detected galaxies, suggesting that tidal interactions may be ongoing. The diffuse cloud does not show a stellar counterpart down to 27 mag arcsec−2 and could be the remnant of these interactions. The analysis of the H I absorption complex in NGC 3100 indicates that the atomic phase of the hydrogen is distributed in the same way as its molecular phase (observed at arcsecond resolution through several carbon monoxide emission lines). We suggest that the interactions occurring within the group are causing turbulent cold gas clouds in the intra-group medium to be slowly accreted towards the centre of NGC 3100. This caused the recent formation of the cold circum-nuclear disc, which is likely sustaining the young nuclear activity.

Places need better planning not less

ABSTRACT The authors writing in this special issue pierce the dark clouds of populist cynicism that fuel rightwing discontent. Do not retreat from the practice of hopeful professional analysis. Embrace and strengthen utopian plans. Include relevant details to attract and inspire popular interest and uptake. Show the inescapable impacts of climate change and the dramatic physical changes that need be done. Nurture a plurality of democratic planning experiments bridging institutional and cultural barriers. Learn to find common cause and commonsense planning together without expecting convergence or unanimity. Foster resilient spatial planning communities using multi-disciplinary expertise honed with practical experience to anticipate and prepare for future uncertainty. Make plans that persuade more than compel. Acknowledge the complexity of cities and the interplay among governments responsible for their fate. Use rational expertise sparingly preparing plans with others.

First detection of the HSO radical in space

We report the discovery of HSO towards several cold dark clouds. The detection is confirmed by the observation of the fine and hyperfine components of two rotational transitions in the protostellar core B1-b, using the Yebes 40 m and IRAM 30 m telescopes. Furthermore, all the fine and hyperfine components of its fundamental transition 10, 1 − 00, 0 at 39 GHz were also detected toward the cyanopolyyne peak of TMC-1. The measured frequencies were used to improve the molecular constants and predict more accurate line frequencies. We also detected the strongest hyperfine component of the 10, 1 − 00, 0 transition of HSO toward the cold dark clouds L183, L483, L1495B, L1527, and Lupus-1A. The HSO column densities were obtained using LTE models that reproduce the observed spectra. The rotational temperature was constrained to 4.5 K in B1-b and TMC-1 using the available Yebes 40 m and IRAM 30 m data. The obtained column densities range between 7.0×1010 cm−2 and 2.9×1011 cm−2, resulting in abundances in the range of (1.4–7.0) × 10−12 relative to H2. Our observations show that HSO is widespread in cold dense cores. However, more observations, together with a detailed comparison with other S-bearing species, are needed to constrain the chemical production mechanisms of HSO, which are not considered in current models.

Denoising Diffusion Probabilistic Models to Predict the Density of Molecular Clouds

We introduce the state-of-the-art deep-learning denoising diffusion probabilistic model as a method to infer the volume or number density of giant molecular clouds (GMCs) from projected mass surface density maps. We adopt magnetohydrodynamic simulations with different global magnetic field strengths and large-scale dynamics, i.e., noncolliding and colliding GMCs. We train a diffusion model on both mass surface density maps and their corresponding mass-weighted number density maps from different viewing angles for all the simulations. We compare the diffusion model performance with a more traditional empirical two-component and three-component power-law fitting method and with a more traditional neural network machine-learning approach. We conclude that the diffusion model achieves an order-of-magnitude improvement on the accuracy of predicting number density compared to that by other methods. We apply the diffusion method to some example astronomical column density maps of Taurus and the infrared dark clouds G28.37+0.07 and G35.39-0.33 to produce maps of their mean volume densities.

The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). IX. Physical Properties and Spatial Distribution of Cores in IRDCs

The initial conditions found in infrared dark clouds (IRDCs) provide insights on how high-mass stars and stellar clusters form. We have conducted high-angular resolution and high-sensitivity observations toward thirty-nine massive IRDC clumps, which have been mosaicked using the 12 and 7 m arrays from the Atacama Large Millimeter/submillimeter Array. The targets are 70 μm dark massive (220–4900 M ⊙), dense (>104 cm−3), and cold (∼10–20 K) clumps located at distances between 2 and 6 kpc. We identify an unprecedented number of 839 cores, with masses between 0.05 and 81 M ⊙ using 1.3 mm dust continuum emission. About 55% of the cores are low-mass (<1 M ⊙), whereas ≲1% (7/839) are high-mass (≳27 M ⊙). We detect no high-mass prestellar cores. The most massive cores (MMC) identified within individual clumps lack sufficient mass to form high-mass stars without additional mass feeding. We find that the mass of the MMCs is correlated with the clump surface density, implying denser clumps produce more massive cores. There is no significant mass segregation except for a few tentative detections. In contrast, most clumps show segregation once the clump density is considered instead of mass. Although the dust continuum emission resolves clumps in a network of filaments, some of which consist of hub-filament systems, the majority of the MMCs are not found in the hubs. Our analysis shows that high-mass cores and MMCs have no preferred location with respect to low-mass cores at the earliest stages of high-mass star formation.

Binary Formation in a 100 μm Dark Massive Core

We report high-resolution ALMA observations toward a massive protostellar core C1-Sa (∼30 M ⊙) in the Dragon infrared dark cloud. At the resolution of 140 au, the core fragments into two kernels (C1-Sa1 and C1-Sa2) with a projected separation of ∼1400 au along the elongation of C1-Sa, consistent with a Jeans length scale of ∼1100 au. Radiative transfer modeling using RADEX indicates that the protostellar kernel C1-Sa1 has a temperature of ∼75 K and a mass of 0.55 M ⊙. C1-Sa1 also likely drives two bipolar outflows, one being parallel to the plane of the sky. C1-Sa2 is not detected in line emission and does not show any outflow activity but exhibits ortho-H2D+ and N2D+ emission in its vicinity; thus it is likely still starless. Assuming a 20 K temperature, C1-Sa2 has a mass of 1.6 M ⊙. At a higher resolution of 96 au, C1-Sa1 begins to show an irregular shape at the periphery, but no clear sign of multiple objects or disks. We suspect that C1-Sa1 hosts a tight binary with inclined disks and outflows. Currently, one member of the binary is actively accreting while the accretion in the other is significantly reduced. C1-Sa2 shows hints of fragmentation into two subkernels with similar masses, which requires further confirmation with higher sensitivity.

Reflections on the State of Marketing: A Dark Cloud or a Bright Star?

Reflections on the State of Marketing: A Dark Cloud or a Bright Star?

The cracks of classical mechanics and the Birth of quantum mechanics

At the end of the 19th century, with the development of Newton's classical mechanics and Maxwell's electromagnetism, a great number of individuals believed that the laws of physics had reached the point of perfection. Physicists like Pierre-Simon Laplace even thought that Newtonian mechanics could be used to calculate the future. However, the "dark clouds" such as the Michelson-Morley experiment and black body radiation demonstrated the flaws of the classical theory. With the efforts of quantum mechanics pioneers such as Planck, Einstein, Schrodinger, and Heisenberg, the discipline of quantum mechanics has gradually developed and has become the key to opening the door to the microscopic world. This paper demonstrates the cracks that occurred in classical physics at the end of the 19th century, and then illustrates the birth of the quantum mechanics and some of the most important concepts of it. Finally, some cutting-edge technologies related to quantum are introduced.

A review on the hypotheses leading to the creation of quantum mechanics

On April 27, 1900, the famous British physicist William Thomson (Baron Kelvin) delivered a speech entitled "The Dark Clouds of the Nineteenth Century on the Theory of Heat and Photodynamics" at the Royal Society. In his speech, he pointed out that, in the "edifice of physics" based on force and heat, there were two hypotheses that could not be solved at that time. One was the ether medium and the other was the black body radiation. Later, the flaws of physics were proved and the quantum mechanics and relativity were thus created. This paper introduces the origin of the concept of aether and the inference of its reality through subsequent scientific experiments. It also illustrates the emergence of a series of hypotheses such as blackbody radiation, which laid the foundation for the beginning of quantum physics.