Circumbinary Planets and the SOLARIS Project

The neutron star binary merger is one of the most energetic phenomena in our Universe. Based on the calculation of gravitational radiation (GR) with the separate consideration of revolution and stellar rotation, and electromagnetic radiation (ER) with unipolar induction DC circuit model and magnetic dipole model, the results are compared to analyse the extent to which the stellar rotation will affect the total gravitational radiation power. Besides, the relationships between radiation power and the related parameters (e.g., orbital radius and stellar mass) are investigated. Furthermore, the feasibility of different types of binary star merger as the progenitor of fast radio bursts and gamma-ray bursts were studied based on the two models of ER, obtaining that binary neutron star and neutron star-white dwarf systems are among the possible progenitors. Finally, the radiation power of both GR and ER are compared under the same conditions. According to the results, the energy dissipation of the system is dominated by gravitational radiation. These results shed lights on further studies on the radiation processes of binary neutron star mergers and binary star systems.

We present the results of hydrodynamic simulations of Jovian mass protoplanets that form in circumbinary discs. The simulations follow the orbital evolution of the binary plus protoplanet system acting under their mutual gravitational forces, and forces exerted by the viscous circumbinary disc. The evolution involves the clearing of the inner circumbinary disc initially, so that the binary plus protoplanet system orbits within a low density cavity. Continued interaction between disc and protoplanet causes inward migration of the planet towards the inner binary. Subsequent evolution can take three distinct paths: (i) the protoplanet enters the 4 : 1 mean motion resonance with the binary, but is gravitationally scattered through a close encounter with the secondary star; (ii) the protoplanet enters the 4 : 1 mean motion resonance, the resonance breaks, and the planet remains in a stable orbit just outside the resonance; (iii) when the binary has initial eccentricity ebin≥ 0.2, the disc becomes eccentric, leading to a stalling of the planet migration, and the formation of a stable circumbinary planet. These results have implications for a number of issues in the study of extrasolar planets. The ejection of protoplanets in close binary systems provides a source of ‘free-floating planets’, which have been discovered recently. The formation of a large, tidally truncated cavity may provide an observational signature of circumbinary planets during formation. The existence of protoplanets orbiting stably just outside a mean motion resonance (4 : 1) in the simulations indicate that such sites may harbour planets in binary star systems, and these could potentially be observed. Finally, the formation of stable circumbinary planets in eccentric binary systems indicates that circumbinary planets may not be uncommon.

Outline of a theory of planet formation in binary systems

Small planets (R p ≤ 4 R ⊕) are divided into rocky super-Earths and gaseous sub-Neptunes separated by a radius gap, but the mechanisms that produce these distinct planet populations remain unclear. Binary stars are the only main-sequence systems with an observable record of the protoplanetary disk lifetime and mass reservoir, and the demographics of planets in binaries may provide insights into planet formation and evolution. To investigate the radius distribution of planets in binary star systems, we observed 207 binary systems hosting 283 confirmed and candidate transiting planets detected by the Kepler mission, then recharacterized the planets while accounting for the observational biases introduced by the secondary star. We found that the population of planets in close binaries (ρ ≤ 100 au) is significantly different from the planet population in wider binaries (ρ > 300 au) or single stars. In contrast to planets around single stars, planets in close binaries appear to have a unimodal radius distribution with a peak near the expected super-Earth peak of R p ∼ 1.3 R ⊕ and a suppressed population of sub-Neptunes. We conclude that we are observing the direct impact of a reduced disk lifetime, smaller mass reservoir, and possible altered distribution of solids reducing the sub-Neptune formation efficiency. Our results demonstrate the power of binary stars as a laboratory for exploring planet formation and as a controlled experiment of the impact of varied initial conditions on mature planet populations.

The Family of stellar systems ranges from binary stars to globular clusters with millions of stars. Binary stars are two stars that are gravitationally bound in a mutual orbit. They are sometimes also termed double stars, but that designation may also include stars that only appear close together in the sky. It is estimated that at least 80% of all stars are members of binary or multiple star systems. Strictly speaking, binaries are multiple stars (S 32), but in common astronomical usage multiple stars are systems with three or more stars.

The advent of gravitational wave (GW) astronomy has provided a new window through which to view and understand the Universe. To fully exploit the potential of GW astronomy, an understanding of all the potential electromagnetic counterparts to a gravitational wave detected source will help maximise the science returns. Here I present a study of the electromagnetic emission from relativistic jets that accompany the merger of binary neutron stars or black hole-neutron star systems. These counterparts provide a probe for the structure and dynamics of these relativistic outflows. Binary neutron star, or neutron star-black hole, mergers are thought to be the dominant progenitor of short gamma-ray bursts (GRBs). Here we investigate the possibility that there is a hidden population of low-Lorentz factor jets resulting in failed GRBs, on-axis orphan afterglows, and what kind of counterparts can be expected given a merger-jet population dominated by these failed-GRB jets. I find that for GW detected mergers, ∼ 80% of the population of on-axis events may result in a failed GRB afterglow. The afterglow of a failed GRB is characterised by the lack of any prompt emission; where the γ-rays are emitted within an optically thick region of the low-Lorentz factor (Γ) outflow and significant suppression via pair production and a high opacity results in the photons coupled to the pair plasma. This plasma will undergo adiabatic expansion, and the photons will decouple at the photospheric radius. The energy in the prompt photons, for a sufficiently low-Γ outflow, will have been significantly suppressed. GW detected mergers have a Malmquist bias towards on-axis events (i.e. the rotational axis of the system), where the peak of the probability distribution is an inclination ∼ 30⁰. If the jets from these mergers have an intrinsic structure out to wider angles, then the majority of mergers will be accompanied by electromagnetic counterparts from these various jet structures. By making some simple assumptions about the energetic structure of a jet outside of a bright core region, the various temporal features that result from a given jet structure can be predicted. Where the population of merger jets is dominated by a single structure model, I show the expected fractions of optical counterparts brighter than m_AB = 21. On 17 August 2017, the Light Interferometer Gravitational Wave Observatory (LIGO) in collaboration with Virgo detected the merger of a binary neutron star system. Various electromagnetic counterparts were detected: the GRB 170817A by Fermi/GBM and INTEGRAL; an optical, blue to red, macro/kilo-nova from ∼ 1/2 day post merger to ∼ 5 − 10 days; and a brightening radio, and X-ray counterpart from ∼ 10 days. Optical detection of this counterpart at a magnitude ∼ 26 was made at ∼ 100 days post-merger. Analysis of this counterpart is consistent with the afterglow of a Gaussian structured jet viewed at the system inclination, ∼ 18 ± 8⁰. If all short GRB jets have a similar jet structure, then the rates of orphan afterglows in deep drilling blind surveys e.g. the Large Synoptic Survey Telescope (LSST), will be higher than those expected from a homogeneous, or ‘top-hat’ jet, population. The rates for the various jet structures for orphan afterglows from mergers are discussed, showing that for a population of failed GRBs, or an intrinsic Gaussian structure, an excess in the orphan rate may be apparent. Understanding the dynamics and structure for the jets from black-hole systems born at the merger of a compact binary can help give clues as to the nature of jets from black holes on all scales. As an aside, I show empirically that regardless of black hole mass or system phenomenology, the relativistic jets from such systems share a universal scaling for the jet power and emitted γ-ray luminosity. This scaling could be due to the similar efficiencies of various processes, or alternatively, the scaling may be able to give insights into the emission and physical processes that are responsible for high-energy photons from these outflows. GW astronomy offers a probe of the most extreme relativistic outflows in the Universe, GRBs. The predicted electromagnetic counterparts from these outflows, in association with GW detections, provides a way to probe the Lorentz-factor distribution for merger-jets. Additionally, the phenomenological shape of the afterglows, at various inclinations, gives an indication of the intrinsic structure of these jets. An understanding of these dynamical and structural qualities can be used to constrain the parent population, merger rates, and binary evolution models for compact binary systems.

We compute quasiequilibrium sequences of synchronously rotating compact binary star systems with constant rest masses. This computation is carried out by using a numerical scheme which is different from the scheme based on the conformally flat assumption about the space. Stars are assumed to be polytropes with polytropic indices of $N=0.5,$ $N=1.0,$ and $N=1.5.$ Since we compute binary star sequences with a constant rest mass, they provide approximate evolutionary tracks of binary star systems. For relatively stiff equations of state $(N<1.0),$ there appear turning points along the quasiequilibrium sequences plotted in the angular momentum---angular velocity plane. Consequently a secular instability against exciting internal motion sets in at those points. Qualitatively, these results agree with those of Baumgarte et al. who employed the conformally flat condition. We further discuss the effect of different equations of state and a different strength of gravity by introducing two kinds of dimensionless quantities which represent the angular momentum and the angular velocity. The strength of gravity is renormalized in these quantities so that the quantities are transformed to values around unity. Therefore we can clearly see relations among quasiequilibrium sequences for a wide variety of strength of gravity and for different compressibility.

The Programmable Liquid-crystal Active Coronagraphic Imager for the DAG telescope (PLACID) will be the world’s first ever “adaptive stellar coronagraph” facility – with “adaptive” referring to the instrument’s unique ability to adjust in real-time to changing observing conditions.The PLACID project achieved a major milestone by being delivered to the Turkish National Observatories (TNO) facilities at Atatürk University, Erzurum in March of 2024 and subsequently being installed on the diffraction-limited Nasmyth platform of the new national observatory, the 4-m DAG (Doğu Anadolu Gözlemevi) telescope during the first semester of 2025. The Assembly, Integration and Validation (AIV) activities are currently ongoing with the internal light source, with first light anticipated by the fall/end of 2025.PLACID consists of a fore-optics coronagraphic intermediate stage platform, positioned between the TROIA extreme adaptive optics (XAO) system and the DIRAC HAWAII-1RG focal-plane array. Its core component is a customized spatial light modulator (SLM) functioning as a programmable scalar focal-plane phase mask (FPM) coronagraph, operating from H- to Ks-band. The dynamically addressed SLM enables software-only adjustments or re-alignments of the FPM pattern, entirely free of actuator motion, offering observers a highly flexible and reconfigurable system.Preparing for the first observations, the PLACID graphics user interface (GUI) is currently being finalized, while the PLACID on-sky discovery space was estimated, based on laboratory measurements at factory acceptance, as well as simulations with post-AO residual wavefront errors. This was conceived to enable the Turkish and visitor astronomers to plan future high-contrast imaging observations. The science discovery space estimate has been derived using an up-to-date exposure time calculator for PLACID, considering key parameters such as adaptive optics performance, contrast levels, limiting magnitudes, and coronagraphic inner working angle.The instrument is particularly promising for exoplanet and circumstellar disk imaging, while new developments of the PLACID GUI are in the works for coronagraphic imaging of binary or multiple star systems — a valuable niche science case for PLACID. Development of the PLACID data reduction software is also currently underway, based on existing high-contrast imaging software architecture (PynPoint).In parallel to PLACID first science observations in 2026, future development avenues for the instrument include:Self-calibration of non-common path aberrations (NCPAs) using a phase-shifting Zernike wavefront sensor, Coronagraphic nulling tailored for binary or triple star systems, compatible with angular differential imaging (ADI), Time-domain coherent differential imaging (CDI). We present the delivered PLACID instrument and its discovery space, detailing its current on-site commissioning status, and — if available at the time — the first on-sky results.

Type Ia supernovae (SNe Ia) are runaway thermonuclear explosions in white dwarfs that result in the disruption of the white dwarf star, and possibly its nearby stellar companion. SNe Ia occur over an immense range of stellar population age and host galaxy environments, and play a critical role in the nucleosynthesis of intermediate-mass and iron-group elements, primarily the production of nickel, iron, cobalt, chromium, and manganese. Though the nature of their progenitors is still not well-understood, SNe Ia are unique among stellar explosions in that the majority of them exhibit a systematic lightcurve relation: more luminous supernovae dim more slowly over time than less luminous supernovae in optical light (intrinsically brighter SNe Ia have broader lightcurves). This feature, unique to SNe Ia, is rather remarkable and allows their peak luminosities to be determined with fairly high accuracy out to cosmological distances via measurement of their lightcurve decline. Further, studying SNe Ia gives us important insights into binary star evolution physics, since it is widely agreed that the progenitors of SNe Ia are binary (possibly multiple) star systems. In this review, we give a current update on the different proposed Type Ia supernova progenitors, including descriptions of possible binary star configurations, and their explosion mechanisms, from a theoretical perspective. We additionally give a brief overview of the historical (focussing on the more recent) observational work that has helped the astronomical community to understand the nature of the most important distance indicators in cosmology.

LIGO and Virgo recently made the first observation of a binary neutron star merger demonstrating that gravitational-wave observations offer the ability to probe how matter behaves in one of the most extreme environments in the Universe. However, the gravitational-wave signal emitted by an inspiraling binary neutron star system is only weakly dependent on the equation of state and extracting this information is challenging. Previous studies have focused mainly on binary systems where the neutron stars are spinning slowly and the main imprint of neutron star matter in the inspiral signal is due to tidal effects. For binaries with non-negligible neutron-star spin the deformation of the neutron star due to its own rotation introduces additional variations in the emitted gravitational-wave signal. Here we explore whether highly spinning binary neutron-star systems offer a better chance to measure the equation-of-state than weakly spinning binary-neutron star systems. We focus on the dominant adiabatic quadrupolar effects and consider three main questions. First, we show that equation-of-state effects can be significant in the inspiral waveforms, and that the spin-quadrupole effect dominates for rapidly rotating neutron stars. Second, we show that variations in the spin-quadrupole phasing are strongly degenerate with changes in the component masses and spins, and therefore neglecting these terms has a negligible impact on the number of observations with second generation observatories. Finally, we explore the bias in the masses and spins that would be introduced by using incorrect equation-of-state terms. Using a novel method to rapidly evaluate an approximation of the likelihood we show that assuming the incorrect equation-of-state when measuring source parameters can lead to a significant bias. We also find that the ability to measure the equation-of-state is improved when considering spinning systems.

In explaining the origin of stellar and planetary systems, contemporary astrophysics has long relied on the "Nebular Hypothesis" and random collision models built upon classical Newtonian mechanics and thermodynamics. While this phenomenological perspective can describe the macroscopic mass aggregation of matter, it fails to reach the "Information Ontology" of celestial evolution within the 4D Manifold. Grounded in the limit topological and dynamical framework of the Grand Unified Theory of Cosmic Mind (GUTCM), this research attempts a systematic geometric reconstruction of the genesis of celestial bodies. This paper proposes that the core macroscopic physical characteristics of celestial bodies—including intrinsic rotation, ecosystem complexity, and composite binary star structures—are fundamentally all holographic geometric projections of the "Information Deadlock" of microscopic wave functions into 3D physical spacetime. This research first strictly defines geometrically: celestial bodies truly possessing "primordial geometric status" are exclusively those evolved directly from the accumulation of elementary particles with truncated deadlocks (substantive inclusions of the absolute vacuum). Because the underlying code of elementary particles exists in an infinitely recursive state of A≡¬A, this high-frequency logical self-reference at the microscopic scale, when superimposed in the same direction within the macroscopic phase space, accurately and inevitably emerges as the "Rotation Effect" of celestial bodies. According to this geometric standard, celestial bodies lacking rotational capability are fundamentally not primordial celestial bodies, but rather "Topological Debris" that have lost their underlying recursive cores following physical collisions of primordial celestial bodies. Furthermore, integrating General Relativity with the 4D information structure, this model re-examines the formation mechanisms of the solar system and the Earth, dispelling the academic myth of linear random evolution. We demonstrate that the mass distribution and macroscopic gravitational destiny of celestial bodies were strictly determined by their allocated "Information Structure and Information Mass (Minfo​)" as early as the Planck instant when the Big Bang singularity (the core of the 4D Riemann sphere) unfolded. The Earth, as a direct informational residue of the singularity, deliberately discarded massive physical mass during its evolution in exchange for ultimate "topological degrees of freedom"; it is precisely this geometric privilege of low physical mass that enables it to exert profound 4D informational gravity, accurately capturing and evolving a holographic ecosystem with a complexity equivalent to the sum total of the entire universe. Finally, this research achieves ultimate holographic isomorphism between microscopic particle physics and macroscopic celestial mechanics: microscopic "Quark Confinement" is perfectly mapped to highly entangled "Binary Star Systems" in the macroscopic universe, proving that composite deadlocked particles still possess absolute topological rigidity and gravitational rebound mechanisms at the macroscopic scale. Simultaneously, this paper elucidates that the "Gluon" sustaining quarks is, in fact, a buffering pivot of a "Möbius Strip" formed by the mutual coiling of two wave functions; in macroscopic celestial systems, it accurately incarnates as the invisible "Barycenter" between binary stars, bearing the limit tension of spacetime curvature, thereby explaining the topological inevitability of gluons acting merely as nodes for force transmission and never accumulating into substantive celestial bodies. This research proves that the universe's microscopic matrix and macroscopic celestial bodies are not two severed physical systems, but a perfectly integrated, precision holographic clock strictly governed by geometric topology and information deadlocks.

Polarimetry is a useful diagnostic of asymmetries in both circumstellar environments and binary star systems. Its sensitivity to asymmetries in systems means that it can help to uncover details about system orbital parameters, including providing information about the orbital inclination. Polarimetry can probe the circumstellar and/or circumbinary material as well. A number of significant results on binary systems have been produced by polarimetric studies. One might therefore expect that polarimetry could similarly play a useful role in studies of exoplanets, and a number of possible diagnostics for exoplanets have been proposed. However, the application of polarimetry to exoplanet research is only in preliminary stages, and the difficulties with applying the technique to exoplanets are non-trivial. This review will discuss the successes of polarimetry in analyzing binary systems, and consider the possibilities and challenges for extending similar analysis to exoplanet systems.

Star catalogue data indicate that only 30 of every 100 stars are alone (Allen, 1973). The rest are in double or multiple star systems. By itself, this finding would be sufficient justification for including binary star systems in a book designed to help its readers explore the nature of our cosmos. But there is much more. Binary stars are a means to obtain masses, sizes, temperatures, and surface details of stars other than the Sun. In other words, they are a major source of fundamental data. If scientists can be thought of as prospectors, binary stars are a rich lode of pure gold.

We present the results of our second radial velocity (RV) monitoring campaign, carried out with the Échelle spectrograph FLECHAS at the University Observatory Jena in the course of the Großschwabhausen binary survey between December 2016 and June 2018. The aim of this project is to obtain precise RV measurements for spectroscopic binary stars in order to redetermine, verify, improve, and constrain their Keplerian orbital solutions. In this paper, we describe the observations, data reduction, and analysis and present the results of this project. In total, we have taken 721 RV measurements of 11 stars and derived well‐determined orbital solutions for nine systems (seven single‐ and two double‐lined spectroscopic binaries) with periods in the range between 2 and 70 days. In addition, we could rule out the orbital solutions for the previously classified spectroscopic binary systems HIP 107136 and HIP 107533, whose radial velocities are found to be constant on the km s−1‐level over a span of time of more than 500 days. In the case of HIP 2225, a significant change of its systematic velocity is detected between our individual observing epochs, indicating the presence of an additional companion, which is located on a wider orbit in this system.

Long–baseline optical interferometry has revolutionised binary star astronomy. This paper reviews some recent binary star work done using the Mark III Stellar Interferometer. For the first time, many spectroscopic binaries, eclipsing binaries, triple systems, and binaries with X-ray sources have had their visual orbit, diameter of the primary component, and color index determined. Also, accurate stellar masses, distances, radii, and effective temperatures have been derived. A preliminary distance to the Hyades cluster has also been determined. In addition, preliminary observations provide evidence of a third body in the binary star system ζ Her, which may resolve an 85-year old discrepancy in astronomy.