Star-like Object Research Articles

General-relativistic thin-shell Dyson megaspheres

Loosely inspired by the somewhat fanciful notion of detecting an arbitrarily advanced alien civilization, we consider a general-relativistic thin-shell Dyson mega-sphere completely enclosing a central star-like object, and perform a full general-relativistic analysis using the Israel--Lanczos--Sen junction conditions. We focus attention on the surface mass density, the surface stress, the classical energy conditions, and the forces between hemispheres. We find that in the physically acceptable region the NEC, WEC, and SEC are always satisfied, while the DEC can be violated if the Dyson mega-sphere is sufficiently close to forming a black hole. We also demonstrate that the original quasi-local version of the maximum force conjecture, F <= {1/4} F_{Stoney} = {1/4} F_{Planck}, can easily be violated if the Dyson mega-sphere is sufficiently compact, that is, sufficiently close to forming a black hole. Interestingly there is a finite region of parameter space where one can violate the original quasi-local version of the maximum force conjecture without violating the DEC. Finally, we very briefly discuss the possibility of nested thin-shell mega-spheres (Matrioshka configurations) and thick-shell Dyson mega-spheres.

SN 1961V: A Pulsational Pair-instability Supernova

We explore a variety of models in which SN 1961V, one of the most enigmatic supernovae (SNe) ever observed, was a pulsational pair-instability supernova (PPISN). Successful models reproduce the bolometric light curve of the principal outburst and, in some cases, the emission 1 yr before and several years afterward. All models have helium-rich ejecta, bulk hydrogenic velocities near 2000 km s−1, and total kinetic energies of (4−8) × 1050 erg. Each eventually leaves behind a black hole remnant. Three subclasses of PPISN models are explored, each with two different choices of carbon abundance following helium burning. Carbon is an important parameter because shell carbon burning can weaken the explosion. The three subclasses correspond to situations where SN 1961V and its immediate afterglow were (a) a single event, (b) the first of two or more pulsational events separated by decades or centuries, or (c) the latter stages of a complex explosion that had already been going on for a year or more. For the low-carbon case, the main-sequence mass for SN 1961V’s progenitor would have been 100−115 M ⊙, its pre-SN helium core mass was 45−52 M ⊙, and the final black hole mass was 40−45 M ⊙. For the high-carbon case, these values are increased by roughly 20%−25%. In some PPISN models, a ∼1040 erg s−1 star-like object could still be shining at the site of SN 1961V, but it has more likely been replaced by a massive accreting black hole.

Link between Morphology, Structure, and Interactions of Composite Microgels.

We combine small-angle scattering experiments and simulations to investigate the internal structure and interactions of composite poly(N-isopropylacrylamide)–poly(ethylene glycol) (PNIPAM–PEG) microgels. At low temperatures the experimentally determined form factors and the simulated density profiles indicate a loose internal particle structure with an extended corona that can be modeled as a starlike object. With increasing temperature across the volumetric phase transition, the form factor develops an inflection that, using simulations, is interpreted as arising from a conformation in which PEG chains are incorporated in the interior of the PNIPAM network. This gives rise to a peculiar density profile characterized by two dense, separated regions, at odds with configurations in which the PEG chains reside on the surface of the PNIPAM core. The conformation of the PEG chains also have profound effects on the interparticle interactions: Although chains on the surface reduce the solvophobic attraction typically experienced by PNIPAM particles at high temperatures, PEG chains inside the PNIPAM network shift the onset of attractive interaction at even lower temperatures. Our results show that by tuning the morphology of the composite microgels, we can qualitatively change both their structure and their mutual interactions, opening the way to explore new collective behaviors of these objects.

Large proper motion of the Thorne–Żytkow object candidate HV 2112 reveals its likely nature as foreground Galactic S-star

Abstract Using the Southern Proper Motion (SPM) catalogue, we show that the candidate Thorne–Żytkow object HV 2112 has a proper motion implying a space velocity of about 3000$\,\rm {km}\,\rm {s}^{-1}$if the object is located at the distance of the Small Magellanic Cloud (SMC). The proper motion is statistically different from that of the SMC at approximately 4σ in SPM, although the result can drop to about 3σ significance by including the UCAC4 data and considering systematic uncertainties in addition to the statistical ones. Assuming the measurement is robust, this proper motion is sufficient to exclude its proposed membership of the SMC and to argue instead that it is likely to be a foreground star in the Milky Way halo. The smaller distance and therefore lower brightness argue against its proposed nature as a Thorne–Żytkow object (the hypothesized star-like object formed when a normal star and a neutron star merge) or a Asymptotic Giant Branch (AGB) star. Instead we propose a binary scenario where this star is the companion of a former massive AGB star, which polluted the object with via its stellar wind, i.e. a special case of an extrinsic S star. Our new scenario solves two additional problems with the two existing scenarios for its nature as Thorne–Żytkow object or present-day super AGB star. The puzzling high ratio of the strength of calcium to iron absorption lines is unexpected for SMC supergiants, but is fully consistent with the expectations for halo abundances. Secondly, its strong variability can now be explained naturally as a manifestation of the Mira phenomenon. We discuss further observational tests that could distinguish between the foreground and SMC scenarios in advance of the improved proper motion measurements likely to come from Gaia.

ORBITAL TRAJECTORY SIMULATION ON TWIN STARS SYSTEM IN IFS FRACTAL MODEL BASED ON HYBRID ANIMATION METHOD

IFS (Iterated Function Systems) is a method to model fractal object based on affine transformation functions. The star-like object rotation effect in the IFS fractal model could be exhibited by using metamorphical method, as a replacement to the affine rotation method on a non metamorphic animation. The advantage of a metamorphic animation method over the metamorphic animation method is that the object's relative position to the fixed point as an absolute centroid is absolute. Therefore, the rotational effect can be exhibited at any positions. In addition, it can also be combined with rotational effect of the local centroid itself around the absolute centroid as a fixed point by the primitive rotational operation to form an interesting behavior of orbital trajectory Based on the hybrid of both animation methods, the animation simulation could be done on orbital trajectory on a twin stars rotating to each other as a system. Both objects are rotated in the same angular direction, but started in the opposite position around two closely different fixed points. So, the orbital trajectory yielded forms an elliptical path. The two similar objects can be created efficiently by cloning-scaling technique. In general, the animation method can be modeled as an animation framework.

A BLUE POINT SOURCE AT THE LOCATION OF SUPERNOVA 2011DH

We present Hubble Space Telescope (HST) observations of the field of the Type IIb supernova (SN) 2011dh in M51 performed at ~1161 rest-frame days after explosion using the Wide Field Camera 3 and near-UV filters F225W and F336W. A star-like object is detected in both bands and the photometry indicates it has negative (F225W - F336W) color. The observed object is compatible with the companion of the now-vanished yellow supergiant progenitor predicted in interacting binary models. We consider it unlikely that the SN is undergoing strong interaction and thus estimate that it makes a small contribution to the observed flux. The possibilities of having detected an unresolved light echo or an unrelated object are briefly discussed and judged unlikely. Adopting a possible range of extinction by dust, we constrain parameters of the proposed binary system. In particular, the efficiency of mass accretion onto the binary companion must be below 50%, if no significant extinction is produced by newly formed dust. Further multiband observations are required in order to confirm the identification of the object as the companion star. If confirmed, the companion star would already be dominant in the UV/optical regime, so it would readily provide a unique opportunity to perform a detailed study of its properties.

Rotational state of the nucleus of Comet 9P/Tempel 1: Results from Hubble Space Telescope observations in 2004

The nucleus of Comet 9P/Tempel 1 was first observed with the Hubble Space Telescope (HST) in December 1997 [Lamy, P., Toth, I., A'Hearn, M.F., Weaver, H., Weissman, P.R., 2001. Icarus 154, 337–344], but the temporal coverage was insufficient to determine its rotational period. Because the success of the Deep Impact mission was critically dependent on understanding the rotational state and approximate shape and size of the nucleus, we extensively re-observed 9P/Tempel 1, this time with the Advanced Camera for Surveys (HST/ACS), from May 7.9 to 9.5, 2004 (UT). At the mid-point of the observing window, the comet was 3.52 AU from the Sun, 4.03 AU from the Earth, and at a solar phase angle of 13.3°. The program was comprised of 18 separate visits, each one corresponding to an HST orbit filled with 3 ACS exposures of either 800 or 857 s duration with the F606W broadband filter. These very deep exposures revealed a star-like object, without any apparent coma. The light curve, defined by 49 data points, is characterized by a mean apparent V magnitude of 21.8 and an amplitude of 0.5 mag, indicating that we were viewing the varying cross-section of a rotating, elongated body. The periodicity was analyzed with seven different techniques yielding a rotational period in the range 39.40 to 43.00 h, and a mean value of 41.27 ± 1.85 h (1 σ). Using an albedo p V = 0.04 and a linear phase law with a coefficient β = 0.0465 mag deg −1 , we determined an effective radius of 3.01 km; a possible prolate spheroid solution has semi-axes a = 3.71 km , b = 2.36 km and a minimum axial ratio a / b ∼ 1.57 . By comparing the light curves obtained in 1997 and in 2004, we were able to constrain the phase function of the nucleus. Finally, an upper limit of A f ρ < 0.04 cm is set based on the non-detection of the coma.

Rotational state of the nucleus of Comet 9P/Tempel 1: Results from Hubble Space Telescope observations in 2004

The nucleus of Comet 9P/Tempel 1 was first observed with the Hubble Space Telescope (HST) in December 1997 [Lamy, P., Toth, I., A'Hearn, M.F., Weaver, H., Weissman, P.R., 2001. Icarus 154, 337–344], but the temporal coverage was insufficient to determine its rotational period. Because the success of the Deep Impact mission was critically dependent on understanding the rotational state and approximate shape and size of the nucleus, we extensively re-observed 9P/Tempel 1, this time with the Advanced Camera for Surveys (HST/ACS), from May 7.9 to 9.5, 2004 (UT). At the mid-point of the observing window, the comet was 3.52 AU from the Sun, 4.03 AU from the Earth, and at a solar phase angle of 13.3°. The program was comprised of 18 separate visits, each one corresponding to an HST orbit filled with 3 ACS exposures of either 800 or 857 s duration with the F606W broadband filter. These very deep exposures revealed a star-like object, without any apparent coma. The light curve, defined by 49 data points, is characterized by a mean apparent V magnitude of 21.8 and an amplitude of 0.5 mag, indicating that we were viewing the varying cross-section of a rotating, elongated body. The periodicity was analyzed with seven different techniques yielding a rotational period in the range 39.40 to 43.00 h, and a mean value of 41.27 ± 1.85 h (1 σ). Using an albedo p V = 0.04 and a linear phase law with a coefficient β = 0.0465 mag deg −1 , we determined an effective radius of 3.01 km; a possible prolate spheroid solution has semi-axes a = 3.71 km , b = 2.36 km and a minimum axial ratio a / b ∼ 1.57 . By comparing the light curves obtained in 1997 and in 2004, we were able to constrain the phase function of the nucleus. Finally, an upper limit of A f ρ < 0.04 cm is set based on the non-detection of the coma.

SDSS J103913.70+533029.7: A Super Star Cluster in the Outskirts of a Galaxy Merger

We describe the serendipitous discovery in the spectroscopic data of the Sloan Digital Sky Survey of a star-like object, SDSSJ103913.70+533029.7, at a heliocentric radial velocity of +1012 km s{sup -1}. Its proximity in position and velocity to the spiral galaxy NGC 3310 suggests an association with the galaxy. At this distance, SDSSJ103913.70+533029.7 has the luminosity of a super star cluster and a projected distance of 17 kpc from NGC 3310. Its spectroscopic and photometric properties imply a mass of > 10{sup 6} M{sub {circle_dot}} and an age close to that of the tidal shells seen around NGC 3310, suggesting that it formed in the event which formed the shells.

Boulware state and semiclassical thermodynamics of black holes in a cavity

A black hole, surrounded by a reflecting shell, acts as an effective star-like object with respect to the outer region that leads to vacuum polarization outside, where the quantum fields are in the Boulware state. We find the quantum correction to the Hawking temperature, taking into account this circumstance. It is proportional to the integral of the trace of the total quantum stress-energy tensor over the whole space from the horizon to infinity. For the shell, sufficiently close to the horizon, the leading term comes from the boundary contribution of the Boulware state.

ROSAT/Chandra observations of a bright transient in M 81

We present a 10-year X-ray light curve and the spectra of a peculiar X-ray transient in the spiral galaxy M81. The source was below the detection limit of ROSAT PSPC before 1993, but it brightened substantially in 1993, with luminosities exceeding the Eddington limit of a 1.5 solar-mass compact accretor. It then faded and was not firmly detected in the ROSAT HRI and PSPC observations after 1994. The Chandra image obtained in 2000 May, however, shows an X-ray source at its position within the instrumental uncertainties. The Chandra source is coincident with a star-like object in the Digitized-Sky-Survey. A Hubble image suggests that the optical object may be extended. While these three observations could be of the same object, which may be an X-ray binary containing a black-hole candidate, the possibility that the ROSAT and Chandra sources are two different objects in a dense stellar environment cannot be ruled out. The Hubble data suggests that the optical object may be a globular cluster yet to be identified.

Heat expansion of star-like cosmic objects induced by the cosmological expansion

The heat expansion of a star-like cosmic object, induced by the cosmological bremsheat production within a moving body, that was predicted by the Projective Unified Field Theory of the author, is approximately treated. The difference to planet-like bodies investigated previously arises from another material constitution. The exponential-like expansion law is applied to a model with numerical values of the Sun. The results are not in contradiction to empirical facts.

Shape representation and recognition based on invariant unary and binary relations

The problem of transformation invariant object recognition is considered. We develop a projective transformation invariant representation for both scene and model which facilitates an attributed relational graph object matching based only on unary and binary relations. The unary and binary measurements used for matching are derived from sets of reference points such as corners and bi-tangent points which are stable under the various transformations considered. Each set of reference points is used to generate a distinct barycentric coordinate basis system associated with one node of the object graph representation. We show that barycentric coordinates of the reference image points can be made invariant under any arbitrary projective transformation. The conditions that must hold for a basis to be valid are stated. We illustrate the construction of the barycentric coordinate systems for the affine and perspective transformations. For the object and scene representation we use the barycentric coordinates of the reference points generating the barycentric coordinate system, together with auxiliary measurements such as colour and texture as the node's unary measurements. For binary measurements we use the product of the barycentric coordinate system for one node with the inverse of the barycentric coordinate system associated with another node. The unary and binary relations provide an orthogonal decomposition of the shape being matched. They are used in a relaxation process to detect instances of objects consistent with a given model. We demonstrate the proposed methodology of projective transformation invariant object representation on several examples. First we illustrate the stability of the shape representation in terms of unary relations both visually and numerically. We then experimentally demonstrated the invariance of binary relations on a star-like object. We show experimentally that the binary relations derived are invariant. The final example demonstrates the proposed approach as a tool for 3D object recognition. The aim is to recognize 3D objects in terms of planar faces. A hexagonal model shape is hypothesized in the image. The only instance of the hypothesized model is successfully recovered.

Is the eclipsing variable EE Cep a cousin of Aur?

ABSTRA C T We report the first five-colour Johnson UBVRI observations of the last eclipse of the longperiod (5.7 yr) eclipsing binary EE Cep. We propose that the star is a member of the Cep OB1 association at a distance of 2.75 kpc. Using this assumption, we find that the primary is a B5 bright giant of radius < 10 R( and luminosity Mv < ˇ3:1. The observations show that the obscuring body is not a star-like object. We suggest that the invisible companion in EE Cep is a dark, thick disc around a low-luminosity central star or binary, and that the system has a few important similarities to the e Aur system.

Statistical sampling and fractal distributions

We report here on work that has its origin in a problem of statistical sampling and that has extended over more than a few years. There are connections with several other areas of mathematics, including convex analysis, tomography, and, perhaps more surprisingly, fractal geometry and iterated function systems. This summary stresses these connections and the more visual aspects of the work. To introduce the ideas we direct the reader's attention to Figure 1. There we see a complicated starlike object sitting inside the regular hexagon. As we shall see, each point in the hexagon encodes three (dependent) coordinates Xk summing to 0. These coordinates provide a set of sampling values that are exactly "balanced"; in the second section of this article we shall say something about the statistical advantages of choosing the balanced sampling points according to a particular distribution within the hexagon, such as that shown in Figure 1. The "superstar" appearing in Figure 1 is a self-similar fractal in the sense of Mandelbrot [M]; it has dimension In 6/ ln 3 ~ 1.631; and it is riddled with infinitely many jagged holes, each bounded by the classic Koch snowflake curve. The superstar inhabits a regular hexagon which we denote by M(3) in this article; think of 3 as the sample size of the corresponding statistical procedure. The superstar may be generated by an iterated function system (IFS), in the sense of Barnsley [B], involving the six maps that shrink (with contraction factor ~) the hexagon M(3) toward its six vertices. The superstar may also be viewed as the support of an uncountable family of extreme points in a certain convex body of probability measures. We'll discuss these matters in more detail a little later. The histogram at the base of Figure 1 records the frequency distribution of the horizontal component of

Deep Search for Optical Counterparts of Gamma-ray Bursters

AbstractPreliminary results are presented of the first (searching) stage of our observational program of the search and study of weak blue star-like objects in the two small γ-ray burst boxes GB 790418 and GB 790613. The basic search purposes are (1) the selection of star-like objects weaker than 23m inside these boxes, (2) the selection of the bluest ones in B — V among these objects. The first result is the fact that there are no blue (with B — V &lt; 0) star-like objects brighter than 24m in both boxes. But in each of these GRB error boxes one blue object with smaller flux was selected for further study to elucidate their nature. In the smallest of the archival GRB error boxes (GB 790613) obtained by three satellite triangulation, the bluest star-like object with V = 24.56(±0.16) and B — V = −0.20(±0.19) is near the center (at the distance &lt; 10") of the GRB box. In the GB 790418 error box, the bluest star-like object with B = 24.40(±0.20), B — V = −0.40(±0.40) is found at ≈50" from the center.

A TWO-DIMENSIONAL BLAST WAVE IN RELATIVISTIC MAGNETOHYDRODYNAMICS

The blast wave produced by a star-like object in a magnetic field is studied numerically in the approximation of ideal, fully relativistic magnetohydrodynamics (MHD). Waves of this type are observed to evolve along three episodes. At early time an outgoing shock front and an ingoing rarefaction wave is established. The ingoing rarefaction wave steepens, and gives rise to dust formation in the core. The steep rarefaction wave front becomes an ingoing shock. An annular region of high magnetic pressure about the equatorial plane deforms this shock front radially, whereby it becomes prolate along the axis of symmetry. The core is subsequently refilled as this shock front converges. Subsequent collapse in the center gives rise to high pressures, familiar from the well-known converging shock problem in nonrelativistic hydrodynamics, and high densities unique to the relativistic description. The results are compared with spherical blast waves in relativistic hydrodynamics, where a similar three episodes can be found and where collapse of the interior shock at the center constitutes a fluid singularity. It remains an open question whether such fluid singularity persists in the full MHD problem. The computations employ the covariant equations of constraint-free MHD in divergence form introduced in earlier work. The magnetic field is kept divergence free to within machine round-off error.

Noncircular axisymmetric stationary spacetimes.

A formalism is presented to treat axisymmetric stationary spacetimes in the most general case, when the stress-energy tensor is not assumed to be circular, so that one cannot make the usual foliation of spacetime into two orthogonal families of two-surfaces. Such a study is motivated by the consideration of rotating relativistic stars with strong toroidal magnetic field or meridional circulation of matter (convection). The formulation is based on a (2+1)+1 of spacetime and the corresponding projections of the Einstein equation. It offers a suitable frame to discuss the choice of coordinates appropriate for the description of asymptotically flat and noncircular axisymmetric spacetimes. We propose a certain class of coordinates which is interpretable in terms of extremal three- and two-surfaces. This choice leads to well-behaved elliptic operators in the equations for the metric coefficients. Consequently, in the case of a starlike object, the proposed corrdinates are global ones, i.e., they can be extended to spatial infinity. These coordinates are also appropriate for obtaining initial conditions for (instability triggered) evolution, since they match naturally with coordinates proposed for dynamical evolution, especially with the maximal time slicing condition. The formulation is written in an entirely two-dimensional covariant form, but, in order to obtain numerical solutions, we also give the complete system of partial differential equations obtained by specialization of the equations to a certain subclass of the proposed coordinates.

The stability of stars with potential-dependent masses

We calculate the effective mass of a spherical star-like object under the assumption that the mass of an object represents a function of the gravitational potential in which it occurs. We show that due to this mass-dependence on the gravitational potential, it is not possible that a star of a larger mass than that of a neutron star shrinks to a point singularity. We present the value of the upper limits to the mass of spherical mass bodies as a function of their radii in a large range of their mass densities.

The unique supernova (1985f) in NGC 4618

view Abstract Citations (82) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The unique supernova (1985f) in NGC 4618. Filippenko, A. V. ; Sargent, W. L. W. Abstract The complete optical spectrum (3200-10,000 A) of supernova 1985f in NGC 4618 is presented. Strong emission lines of O, Ca, C, Mg, Na, Fe and N are present, while H and He absorption lines are conspicuously absent. The spectrum of SN 1985f does not resemble any previously published spectra of supernovae, and it is postulated that its progenitor was a massive Wolf-Rayet star that expelled its outer atmosphere of H and He prior to supernova explosion. Photographs of SN 1985f are provided which illustrate its location in very bright H II regions near the nucleus of NGC 4618. The supernova, so faint at the time of discovery, is overwhelmed by light from the surrounding galaxy in any moderately deep image. A plate obtained in May 1914 reveals the absence of a starlike object at the expected position, and visual observations made in November 1985 indicate that the supernova has faded substantially since March 1985. Publication: The Astronomical Journal Pub Date: April 1986 DOI: 10.1086/114051 Bibcode: 1986AJ.....91..691F Keywords: Astronomical Spectroscopy; Supernovae; Visible Spectrum; Emission Spectra; Galactic Nuclei; H Ii Regions; Metallicity; Wolf-Rayet Stars; Astrophysics full text sources ADS | data products NED (6) SIMBAD (4)