Subsequent Merger Research Articles

Close Encounters of Wide Binaries Induced by the Galactic Tide: Implications for Stellar Mergers and Gravitational-wave Sources

A substantial fraction of stars can be found in wide binaries with projected separations between ∼102 and 105 au. In the standard lore of binary physics, these would evolve as effectively single stars that remotely orbit one another on stationary Keplerian ellipses. However, embedded in their Galactic environment, the low binding energy of wide binaries makes them exceptionally prone to perturbations from the gravitational potential of the Milky Way and encounters with passing stars. Employing a fully relativistic N-body integration scheme, we study the impact of these perturbations on the orbital evolution of wide binaries along their trajectory through the Milky Way. Our analysis reveals that the torques exerted by the Galaxy can cause large-amplitude oscillations of the binary eccentricity to 1 − e ≲ 10−8. As a consequence, the wide binary members pass close to each other at periapsis, which, depending on the type of binary, potentially leads to a mass transfer or collision of stars or to an inspiral and subsequent merger of compact remnants due to gravitational-wave radiation. Based on a simulation of 105 wide binaries across the Galactic field, we find that this mechanism could significantly contribute to the rate of stellar collisions and binary black hole mergers as inferred from observations of luminous red novae and gravitational-wave events by LIGO/Virgo/Kagra. We conclude that the dynamics of wide binaries, despite their large mean separation, can give rise to extreme interactions between stars and compact remnants.

Asymmetric Learning in Successive Mergers and Acquisitions: Overconfidence and Loss Aversion

Using data from 865 acquisition events launched by Chinese A-share listed companies between 2013 and 2019, we divide the dataset into two subsamples: first-time merger successes and first-time merger failures. For firms that experienced initial merger success, we find the outcomes of their subsequent merger activities to be negative, as managerial overconfidence hindered the assimilation of valuable insights from the initial successful experience. Conversely, in the case of firms that encountered initial merger failure, managerial loss aversion stimulated a learning process that led to improved performance in subsequent merger endeavors. Asymmetric learning effects are observed to significantly impact the merger outcomes of serial acquirers. Further analysis reveals that managerial age plays a role in optimizing this asymmetric learning effect.

Betelgeuse as a Merger of a Massive Star with a Companion

We investigate the merger between a 16M ⊙ star, on its way to becoming a red supergiant (RSG), and a 4M ⊙ main-sequence companion. Our study employs three-dimensional hydrodynamic simulations using the state-of-the-art adaptive mesh refinement code Octo-Tiger. The initially corotating binary undergoes interaction and mass transfer, resulting in the accumulation of mass around the companion and its subsequent loss through the second Lagrangian point (L2). The companion eventually plunges into the envelope of the primary, leading to its spin-up and subsequent merger with the helium core. We examine the internal structural properties of the post-merger star, as well as the merger environment and the outflow driven by the merger. Our findings reveal the ejection of approximately ∼0.6 M ⊙ of material in an asymmetric and somewhat bipolar outflow. We import the post-merger stellar structure into the MESA stellar evolution code to model its long-term nuclear evolution. In certain cases, the post-merger star exhibits persistent rapid equatorial surface rotation as it evolves in the H–R diagram toward the observed location of Betelgeuse. These cases demonstrate surface rotation velocities of a similar magnitude to those observed in Betelgeuse, along with a chemical composition resembling that of Betelgeuse. In other cases, efficient rotationally induced mixing leads to slower surface rotation. This pioneering study aims to model stellar mergers across critical timescales, encompassing dynamical, thermal, and nuclear evolutionary stages.

Contact tracing of binary stars: Pathways to stellar mergers

Stellar mergers are responsible for a wide variety of phenomena such as rejuvenated blue stragglers, highly magnetised stars, spectacular transients, iconic nebulae, and stars with peculiar surface chemical abundances and rotation rates. Before stars merge, they enter a contact phase. Here, we investigate which initial binary-star configurations lead to contact and classical common-envelope (CE) phases and assess the likelihood of a subsequent merger. To this end, we computed a grid of about 6000 detailed 1D binary evolution models with initial component masses of 0.5 − 20.0 M⊙ at solar metallicity. Both components were evolved, and rotation and tides were taken into account. We identified five mechanisms that lead to contact and mergers: runaway mass transfer, mass loss through the outer Lagrange point L2, expansion of the accretor, orbital decay because of tides, and non-conservative mass transfer. At least 40% of mass-transferring binaries with initial primary-star masses of 5 − 20 M⊙ evolve into a contact phase; > 12% and > 19% likely merge and evolve into a CE phase, respectively. Because of the non-conservative mass transfer in our models, classical CE evolution from late Case-B and Case-C binaries is only found for initial mass ratios qi < 0.15 − 0.35. For larger mass ratios, we find stable mass transfer. In early Case-B binaries, contact occurs for initial mass ratios qi < 0.15 − 0.35, while in Case-A mass transfer, this is the case for all qi in binaries with the initially closest orbits and qi < 0.35 for initially wider binaries. Our models predict that most Case-A binaries with mass ratios of q < 0.5 upon contact mainly get into contact because of runaway mass transfer and accretor expansion on a thermal timescale, with subsequent L2-overflow in more than half of the cases. Thus, these binaries likely merge quickly after establishing contact or remain in contact only for a thermal timescale. On the contrary, Case-A contact binaries with higher mass ratios form through accretor expansion on a nuclear timescale and can thus give rise to long-lived contact phases before a possible merger. Observationally, massive contact binaries are almost exclusively found with mass ratios q > 0.5, confirming our model expectations. Because of non-conservative mass transfer with mass transfer efficiencies of 15 − 65%, 5 − 25%, and 25 − 50% in Case-A, -B, and -C mass transfer, respectively (for primary-star masses above 3 M⊙), our contact, merger, and classical CE incidence rates are conservative lower limits. With more conservative mass transfer, these incidences would increase. Moreover, in most binaries, the non-accreted mass cannot be ejected, raising the question of the further evolution of such systems. The non-accreted mass may settle into circumstellar and circumbinary disks, but could also lead to further contact systems and mergers. Overall, contact binaries are a frequent and fascinating result of binary mass transfer of which the exact outcomes still remain to be understood and explored further.

‘Brokering a postcolonial Malaysia: how local elites shaped the Cobbold Commission, 1961–63’

ABSTRACT Sabah’s decolonization and subsequent merger with Malaysia was fraught with uncertainty. The 1962 Cobbold Commission of Enquiry in British Borneo aggravated regional tensions in Southeast Asia and sparked allegations of neo-colonialism. While Orthodox scholarship argues that the commission delivered a decisive cross-section of public opinion, fresh analysis of archival material indicates that its outcomes were compromised by logistical and functional limitations. Through recovering key local voices and disentangling commission addenda from the archive, this paper shows how the inquiry became a vehicle for local elite advancement and Anglo-Malayan geopolitical agenda, rather than transparent democratic legitimation. Furthermore, it contends that the pre-emptive (rather than post factum) nature of the inquiry laid bare its political potentiality. The inconclusiveness of its findings led many to dismiss Sabah’s public as incapable of determining its own future, prompting Britain and Malaya to push ahead with Projek Malaysia [the Malaysia plan] largely irrespective of public opinion. The subsequent push to form Malaysia contributed to deteriorating relations with neighbouring states and ushered a period of marked geopolitical instability. This paper argues, however, that a key, understudied outcome of the commission was the crystallization of local elite voices. Many elites—traditional headmen and local power brokers—claimed to speak for thousands of followers and thus utilized the commission to cement political influence in the postcolonial arena. By casting light on colonial political devices amidst the end of empire, this paper offers valuable nuance and a portable methodology for understanding a range of cognate decolonization experiences.

Exploring the Impact of Galactic Interactions and Mergers on the Central Star Formation of APEX/EDGE–CALIFA Galaxies

Galactic interactions and subsequent mergers are a paramount channel for galaxy evolution. In this work, we use the data from 236 star-forming CALIFA galaxies with integrated molecular gas observations in their central region (approximately within an effective radius)—from the APEX millimeter telescope and the CARMA millimeter telescope array. This sample includes isolated (126 galaxies) and interacting galaxies in different merging stages (110 galaxies; from pairs, merging, and postmerger galaxies). We show that the impact of interactions and mergers in the center of galaxies is revealed as an increase in the fraction of molecular gas (compared to isolated galaxies). Furthermore, our results suggest that the change in star formation efficiency is the main driver for both an enhancement and/or suppression of the central star formation—except in merging galaxies where the enhanced star formation appears to be driven by an increase of molecular gas. We suggest that gravitational torques due to the interaction and subsequent merger transport cold molecular gas inwards, increasing the gas fraction without necessarily increasing star formation.

Distinguishing Dark Matter Cusps from Cores Using Globular Clusters

Globular clusters (GCs) provide valuable insight into the properties of their host galaxies’ dark matter halos. Using N-body simulations incorporating semianalytic dynamical friction and GC−GC merger prescriptions, we study the evolution of GC radial distributions and mass functions in cuspy and cored dark matter halos. Modeling the dynamics of the GC-rich system in the dwarf galaxy UGC 7369, we find that friction-induced inspiral and subsequent mergers of massive GCs can naturally and robustly explain the mass segregation of the GCs and the existence of a nuclear star cluster (NSC). However, the multiple mergers required to form the NSC only take place when the dark matter halo is cuspy. In a cored halo, stalling of the dynamical friction within the core halts the inspiral of the GCs, and so the GC merger rate falls significantly, precluding the formation of an NSC. We therefore argue that the presence of an NSC requires a cusp in UGC 7369. More generally, we propose that the presence of an NSC and the corresponding alteration of the GC mass function due to mergers may be used as an indicator of a cuspy halo for galaxies in which we expect NSC formation to be merger dominated. These observables represent a simple, powerful complement to other inner halo density profile constraint techniques and should allow for straightforward extension to larger samples.

The history of state-corporate relations in South Korea

The purpose of the study is to present the history of relations between the state and big business (chaebol). The characteristic features of the change in the economic life of the Republic of Korea, related to scientific and technical progress, revolutionary processes and global challenges of the world economy are analyzed. The characteristic features of the South Korean economy are analyzed, the methods used by the state to overcome economic shocks, the role of government assistance in the field of corporate nationalization is highlighted. The methodology is based on general scientific special research methods, among which it is necessary to distinguish the dialectical method of scientific knowledge and general scientific methods of knowledge. A systematic approach was used to substantiate the patterns of development of the world economy, structural analysis (for the analysis of transformational changes in the country’s economy)..Scientific novely. The article shows that the economy of South Korea survived the economic depression, and transnational processes accelerate the transition and the formation of a total digital economy in South Korea not only in production processes, but also in all spheres of Korean society’s life and its adaptation during the Fourth Industrial Revolution. It was determined that throughout history the government of the Republic of Korea interfered in the economic activities of the state, trying to control the economy. Conclusions. It is proved that the processes of corporate transnationalization of the Korean economy played an important role in its modern formation, competitive leadership and entry into the global high-tech business environment, which resulted in the country’s rapid transition to the Fourth Industrial Revolution (digital revolution) with the integration of the latest digital technologies and their subsequent adaptation not only in the automation of production processes with minimal human intervention, but also in all spheres of life in Korean society.It is indicated that in order to apply the experience of South Korea to Ukraine, the following problems should be solved: lack of labor force reserve. a significant level of budget expenditures for social protection, an aging population, a low level of savings and a low probability of forced mobilization of funds, the political unacceptability of dictatorship and the subsequent merger of the state and big business.

The Structure of the Universe in the Quasar Absorption Spectra

An analysis of the absorption lines observed in the spectra of quasars makes it possible to study the evolution of the structure of the Universe up to redshifts z∼5. The observed clustering of C IV lines demonstrates the multiple birth of low-mass galaxies in separate structural elements—filaments and “pancakes.” This ensures their subsequent regular hierarchical merger in the central galaxy or group of galaxies. Remnants of the early “pancakes” are observed today as the Local Group, groups around the Andromeda and Centaurus galaxies, and other small groups of galaxies. In turn, the observed clustering of Lyman-alpha lines shows that starless dark matter (DM) halos are also formed in structural elements and their hierarchical clustering leads to the formation of massive starless dark matter halos of moderate density, which also appear in numerical models.

Massive Star Formation in Overdense Regions of the Early Universe

Both the origin of, and the population demographics of, massive black holes (MBHs) remains an open question in modern day astrophysics. Here we introduce the BlackDemon suite of cosmological simulations using the Enzo code. The suite consists primarily of three, high resolution, distinct regions, each with a side length of 1 h$^{-1}$ Mpc. Two of the regions evolve within a larger overdense region while the other evolves within a more `normal' region. The simulation suite has spatial and mass resolution capable of resolving the formation of the first galaxies and MBHs within each region. We report here, as the first in a series of papers, the evolution of the simulation suite up to the point where star formation has commenced in each region and for 2 Myr after the onset of star formation. Within these environments the masses of the first objects to form have masses between approximately 100 M$_{\odot}$ and $10^4$ M$_{\odot}$. The larger mass objects form due to both major mergers, which trigger rapid mass inflow to the centre of the halo, and also through multiple minor mergers which allows the host halo to grow to close to the atomic cooling threshold. In both scenarios the initially very high accretion rates quickly grow the objects to close to $10^4$ M$_{\odot}$. However, accretion halts after less than 50,000 years due to gas starvation. The final fate of these objects in terms of fragmentation and subsequent fragment mergers cannot be deduced at our current resolution. In the case where fragmentation is mild such objects are likely to form super-massive stars before contracting to the main sequence evolving into massive population III stars and subsequently MBHs.

The first quiescent galaxies in TNG300

ABSTRACT We identify the first quiescent galaxies in TNG300, the largest volume of the IllustrisTNG cosmological simulation suite, and explore their quenching processes and time evolution to z = 0. We find that the first quiescent galaxies with stellar masses M* > 3 × 1010 M⊙ and specific star formation rates sSFR < 10−11 yr−1 emerge at z ∼ 4.2 in TNG300. Suppression of star formation in these galaxies begins with a thermal mode of active galactic nucleus feedback at z ∼ 6, and a kinetic feedback mode acts in each galaxy by z ∼ 4.7 to complete the quenching process, which occurs on a time-scale of ∼0.35 Gyr. Surprisingly, we find that the majority of these galaxies are not the main progenitors of their z = 0 descendants; instead, four of the five galaxies fall into more massive galaxies in subsequent mergers at a range of redshifts 2.5 < z < 0.2. By z = 0, these descendants are the centres of galaxy clusters with average stellar masses of 8 × 1011 M⊙. We make predictions for the first quenched galaxies to be located by the JWST.

An observationally derived kick distribution for neutron stars in binary systems

ABSTRACT Understanding the natal kicks received by neutron stars (NSs) during formation is a critical component of modelling the evolution of massive binaries. Natal kicks are an integral input parameter for population synthesis codes, and have implications for the formation of double NS systems and their subsequent merger rates. However, many of the standard observational kick distributions that are used are obtained from samples created only from isolated NSs. Kick distributions derived in this way overestimate the intrinsic NS kick distribution. For NSs in binaries, we can only directly estimate the effect of the natal kick on the binary system, instead of the natal kick received by the NS itself. Here, for the first time, we present a binary kick distribution for NSs with low-mass companions. We compile a catalogue of 145 NSs in low-mass binaries with the best available constraints on proper motion, distance, and systemic radial velocity. For each binary, we use a three-dimensional approach to estimate its binary kick. We discuss the implications of these kicks on system formation, and provide a parametric model for the overall binary kick distribution, for use in future theoretical modelling work. We compare our results with other work on isolated NSs and NSs in binaries, finding that the NS kick distributions fit using only isolated pulsars underestimate the fraction of NSs that receive low kicks. We discuss the implications of our results on modelling double NS systems, and provide suggestions on how to use our results in future theoretical works.

Super-critical accretion of medium-weight seed black holes in gaseous proto-galactic nuclei

ABSTRACT Accretion at sustained or episodic super-Eddington (SE) rates has been proposed as a pathway to grow efficiently light seeds produced by Pop-III stars. We investigate if SE accretion can be sustained onto a black hole (BH) with MBH ∼ 103 M⊙ in the centre of a gas-rich proto-galaxy at z = 15. We perform high-resolution smoothed-particle hydrodynamical simulations, including two different sub-grid models for SE accretion, one based on the slim disc paradigm, and one inspired by recent radiation-magnetohydrodynamical simulations by Jiang and collaborators. Radiative feedback has the form of a thermal dump to surrounding gas particles, with the radiative efficiency being set according to the different SE accretion models. We find that, in all simulations, star formation, BH feedback, and interactions between clumps and the BH rapidly quench accretion after ∼1 Myr, irrespective of the sub-grid model used for accretion. Quenching is stronger in the model based on the simulations of Jiang and collaborators relative to the slim disc model because of its higher radiative efficiency. The SE growth phase is always very brief, lasting a few 0.1 Myr. In the most optimistic case, the BH reaches a mass of ∼104 M⊙. We extrapolate the final BH masses from z = 15 to z ∼ 6, assuming subsequent galaxy mergers will replenish the gas reservoir and trigger new cycles of SE accretion. We find that at most BH seeds would grow to ∼106 M⊙, comparable to the mass of massive BHs in spiral galaxies such as the Milky Way, but falling short of the mass of the high-redshift quasars.

Intellectual Capital in Cross Border Mergers & Acquisitions: An Exaptation Perspective

Exaptation, in internationalization, is defined as the re-use of capabilities that a firm developed through domestic geographical dispersion in the process of cross border mergers and acquisitions (CBMA). This study tests the impacts of exaptation with a firm’s first and subsequent cross border mergers and acquisition engagements. The study is based on the 10 years of data from 2009 to 2019 of 99 manufacturing sector companies of Malaysia to test the relationship between the firm’s domestic geographical dispersion and chances to engage in first-time and subsequent CBMA. We applied pooled regression to estimate hurdle models. The results showed a positive and statistically significant influence of exaptation of control and coordination capabilities on the firm’s probability of engaging first-time cross-border mergers and acquisitions; however, these capabilities become irrelevant in subsequent CBMA involvement. The findings imply that firms operating in geographically dispersed business units can have higher chances of success in cross border mergers and acquisitions.

Does risk disclosure influence mergers and acquisitions? A textual analysis

ABSTRACT Using textual analysis and the data of China’s A-share listed companies from 2010 to 2020, this study examines how risk disclosure in annual reports influences subsequent mergers and acquisitions (M&A). The empirical results show that the risk disclosure tone of annual reports is positively associated with the probability of engaging in M&A deals and bid premium, but is negatively associated with long-term stock returns. Furthermore, the level of risk disclosure in annual reports exerts a negative impact on the probability of all-cash bids and bid premium, but positively associated with the long-term M&A performance, indicating that risk disclosure helps alleviate the information asymmetry between acquirers and targets. The empirical evidence highlights the value relevance of risk disclosure content in annual reports, and the importance in strengthening the supervision of qualitative information disclosure.

Signatures of the Many Supermassive Black Hole Mergers in a Cosmologically Forming Massive Early-type Galaxy

We model here the merger histories of the supermassive black hole (SMBH) population in the late stages of a cosmological simulation of a ∼ 2 × 1013 M ⊙ galaxy group. The gravitational dynamics around the several tens of SMBHs (M • > 7.5 × 107 M ⊙) hosted by the galaxies in the group is computed at high accuracy using regularized integration with the KETJU code. The 11 SMBHs that form binaries and a hierarchical triplet eventually merge after hardening through dynamical friction, stellar scattering, and gravitational wave (GW) emission. The binaries form at eccentricities of e ∼ 0.3–0.9, with one system evolving to a very high eccentricity of e = 0.998, and merge on timescales of a few tens to several hundred megayears. During the simulation, the merger-induced GW recoil kicks eject one SMBH remnant from the central host galaxy. This temporarily drives the galaxy off the M •–σ ⋆ relation; however, the galaxy returns to the relation due to subsequent galaxy mergers, which bring in new SMBHs. This showcases a possible mechanism contributing to the observed scatter of the M •–σ ⋆ relation. Finally, we show that pulsar timing arrays and LISA would be able to detect parts of the GW signals from the SMBH mergers that occur during the ∼4 Gyr time span simulated with KETJU.

Social nucleation: Group formation as a phase transition

The spontaneous formation and subsequent growth, dissolution, merger, and competition of social groups bears similarities to physical phase transitions in metastable finite systems. We examine three different scenarios, percolation, spinodal decomposition, and nucleation, to describe the formation of social groups of varying size and density. In our agent-based model, we use a feedback between the opinions of agents and their ability to establish links. Groups can restrict further link formation, but agents can also leave if costs exceed the group benefits. We identify the critical parameters for costs and benefits and social influence to obtain either one large group or the stable coexistence of several groups with different opinions. Analytic investigations allow us to derive different critical densities that control the formation and coexistence of groups. Our approach sheds light on the early stage of network growth and the emergence of large connected components.

Resilience of sloshing cold fronts against subsequent minor mergers

ABSTRACTMinor mergers are common in galaxy clusters. They have the potential to create sloshing cold fronts (SCFs) in the intracluster medium of the cluster. However, the resilience of SCFs to subsequent minor mergers is unknown. Here we investigate the extent to which SCFs established by an off-axis minor merger are disrupted by a subsequent minor merger. We perform a suite of 13 hydrodynamic + N-body simulations of idealized triple cluster mergers in which we vary the approach direction and impact parameter of the tertiary cluster. Except for ∼1 Gyr after the first core passage of the tertiary cluster, clear SCFs are present in all merger configurations. Subsequent head-on minor mergers reduce the number of SCFs significantly, while subsequent off-axis minor mergers only moderately reduce the number of SCFs. In particular, outer ($\gtrapprox 500\,$kpc) SCFs are resilient. The results of this work indicate that SCFs are easily formed in the course of a minor merger and are long-lived even if a further minor merger takes place. SCFs thus should be ubiquitous, but deriving the merger history of a given cluster based on its observed SCFs might be more complex than previously thought.

Galaxy Core Formation by Supermassive Black Hole Binaries: The Importance of Realistic Initial Conditions and Galaxy Morphology

Abstract The binding energy liberated by the coalescence of supermassive black hole (SMBH) binaries during galaxy mergers is thought to be responsible for the low density cores often found in bright elliptical galaxies. We use high-resolution N-body and Monte Carlo techniques to perform single and multistage galaxy merger simulations and systematically study the dependence of the central galaxy properties on the binary mass ratio, the slope of the initial density cusps, and the number of mergers experienced. We study both the amount of depleted stellar mass (or mass deficit), M def, and the radial extent of the depleted region, r b. We find that r b ≃ r SOI and that M def varies in the range of 0.5–4M •, with r SOI the influence radius of the remnant SMBH and M • its mass. The coefficients in these relations depend weakly on the binary mass ratio and remain remarkably constant through subsequent mergers. We conclude that the core size and mass deficit do not scale linearly with the number of mergers, making it hard to infer merger histories from observations. On the other hand, we show that both M def and r b are sensitive to the morphology of the galaxy merger remnant, and that adopting spherical initial conditions, as done in early work, leads to misleading results. Our models reproduce the range of values for M def found in most observational work, but span nearly an order-of magnitude range around the true ejected stellar mass.

Black Hole Leftovers: The Remnant Population from Binary Black Hole Mergers

Abstract The inspiral and merger of two black holes produces a remnant black hole with mass and spin determined by the properties of its parent black holes. Using the inferred population properties of component black holes from the first two and a half observing runs of Advanced LIGO and Virgo, we calculate the population properties of the leftover remnant black holes. By integrating their rate of formation over the age of the universe, we estimate the number density of remnant black holes today. Using simple prescriptions for the cosmic star formation rate and black hole inspiral delay times, we determine the number density of this leftover black hole population to be , corresponding to ∼60,000 black hole remnants per Milky Way–equivalent galaxy. The mass spectrum of these remnants starts at ∼10 M ⊙ and can be approximated by a decreasing exponential with characteristic length ∼15 M ⊙, the final spin distribution is sharply peaked at χ f ∼ 0.7, and the kick velocities range from tens to thousands of kilometers per second. These kick velocities suggest that globular clusters and nuclear star clusters may retain up to and of their remnant black holes, respectively, while young star clusters would only retain a few tenths of a percent. The estimates in this work assume that none of the remnants participate in subsequent hierarchical mergers. If hierarchical mergers occur, the overall number density would drop accordingly and the remnant mass distribution shape would evolve over time. This population of leftover black holes is an inescapable result from gravitational-wave observations of binary black hole mergers.