Stellar Birth and Death

Advanced LIGO and Advanced Virgo are detecting a large number of binary stellar origin black hole (BH) mergers. A promising channel for accelerated BH merger lies in active galactic nucleus (AGN) discs of gas around supermasssive BHs. Here, we investigate the relative number of compact object (CO) mergers in AGN disc models, including BH, neutron stars (NS), and white dwarfs, via Monte Carlo simulations. We find the number of all merger types in the bulk disc grows ∝ t1/3 which is driven by the Hill sphere of the more massive merger component. Median mass ratios of NS–BH mergers in AGN discs are $\tilde{q}=0.07\pm 0.06(0.14\pm 0.07)$ for mass functions (MF) M−1(− 2). If a fraction fAGN of the observed rate of BH–BH mergers (RBH–BH) come from AGN, the rate of NS–BH (NS–NS) mergers in the AGN channel is ${R}_{\mathrm{ BH}\!-\!\mathrm{ NS}} \sim f_{\mathrm{ AGN}}[10,300]\, \rm {Gpc}^{-3}\, \rm {yr}^{-1},({\mathit{ R}}_{NS\!-\!NS} \le \mathit{ f}_{AGN}400\, \rm {Gpc}^{-3}\, \rm {yr}^{-1}$). Given the ratio of NS–NS/BH–BH LIGO search volumes, from preliminary O3 results the AGN channel is not the dominant contribution to observed NS–NS mergers. The number of lower mass gap events expected is a strong function of the nuclear MF and mass segregation efficiency. CO merger ratios derived from LIGO can restrict models of MF, mass segregation, and populations embedded in AGN discs. The expected number of electromagnetic (EM) counterparts to NS–BH mergers in AGN discs at z < 1 is $\sim [30,900]\, {\rm {yr}}^{-1}(f_{\mathrm{ AGN}}/0.1)$. EM searches for flaring events in large AGN surveys will complement LIGO constraints on AGN models and the embedded populations that must live in them.

view Abstract Citations (26) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stationary stars are axisymmetric. Lindblom, L. Abstract The final state of thermonuclear evolution of a star may consist of either a black hole or an 'ordinary' star such as a white dwarf or neutron star. For the case of black holes, a great deal is known about the structure of this final stationary state; in particular, Hawking (1972) has shown that stationary black holes are axisymmetric. An extension of this result is presented which includes the 'ordinary' final state of stars. It is shown that a stationary star, consisting of a viscous heat-conducting general-relativistic fluid, must be axisymmetric. For this proof, the star is assumed to be embedded in an asymptotically Minkowskian spacetime manifold. The functions which describe the geometry and the fluid of the star are assumed to satisfy certain smoothness conditions. Publication: The Astrophysical Journal Pub Date: September 1976 DOI: 10.1086/154674 Bibcode: 1976ApJ...208..873L Keywords: Black Holes (Astronomy); Neutron Stars; Stellar Evolution; White Dwarf Stars; Conductive Heat Transfer; Gravitational Collapse; Nuclear Fusion; Relativity; Stellar Rotation; Symmetry; Astrophysics full text sources ADS |

Section I. Halo White Dwarfs and Galactic Structure. Old Ultracool White Dwarfs as Cosmological Probes. Number counts of white dwarfs: the impact of GAIA. Influence of Metallicity in the Determination of the Age of Halo White Dwarfs. Cool Halo White Dwarfs from GSCII. Dark halo baryons not in ancient white dwarfs? White Dwarfs in 2QZ and Sloan Surveys. White Dwarfs and Cataclysmic in the FBS. White Dwarfs in Globular Clusters. Core/Envelope Symmetry in Pulsating White Dwarfs Stars. A Search for Variability in Cool White Dwarf Stars. Planetary Nebulae and the Galactic Bulge. Section II. Type Ia Supernovae. Type Ia Supernovae and Cosmology. The Progenitors of Type Ia Supernovae. Progenitors of Supernovae Type Ia. Polulation synthesis for progenitors of type Ia supernovae. How far can we trust SNE Ia as Standard Candles? Kirshner on White Dwarfs. Supernovae. and Cosmology. Section III. Cataclysmic Variables and White Dwarf Accretion. Accretion in Cataclysmic Variable Stars. White Dwarfs in Cataclysmic Variables: Probes of Accretion History. Intermediate Polars in Low States. Chemical Abundances of WDs in CVs. AM CVn Stars in the UCT CCD CV Survey. TUG Observations of V2275 Cyg, RW Umi, PX And and FO Per. The Possible Identification of Two Hibernating Novae. Evidence for large superhumps in TX Col and V4742 Sgr. Concluding remarks.

A significant fraction of the stellar population in the cusp around central\nblack holes of galaxies consists of compact remnants of evolved stars, such as\nwhite dwarfs, neutron stars and stellar mass black holes. We estimate the rate\nof capture of compact objects by massive central black holes, assuming most\nspiral galaxies have a central black hole of modest mass ($\\sim 10^6 \\msun$),\nand a cuspy spheroid. It is likely that the total capture rate is dominated by\nnucleated spirals. We estimate the flux of gravitational wave radiation from\nsuch coalescences, and the estimated detectable source count for proposed\nspace--based gravitational wave observatories such as LISA. About one event per\nyear should be detectable within $1 \\, {\\rm Gpc}$, given very conservative\nestimates of the black hole masses and central galactic densities. We expect\n$10^2$--$10^3$ detectable sources at lower frequencies ($10^{-4}$ Hz) ``en\nroute'' to capture. If stellar mass black holes are ubiquitous, the signal may\nbe dominated by stellar mass black holes coalescing with massive black holes.\nThe rate of white dwarf--white dwarf mergers in the cores of nucleated spirals\nis estimated at $\\sim10^{-6}$ per year per galaxy.\n

In the previous discussion of stellar evolution it has frequently been remarked that, so long as the stellar material remains in the form of an ideal classical gas, its central temperature can only increase as it evolves. This result was originally deduced from the Virial Theorem (3.24) on page 55. As I have mentioned on page 201 in Chapter 9, there is at present no completely clear solution to the problem of what happens to a star whose central temperature is still rising at the time that nuclear fusion reactions have converted the central regions to iron, although the association with supernovae of type II seems highly probable; in fact, as I shall explain in the last section of this chapter, the problem can arise even earlier than that. However, if the centre of the star ceases to be an ideal classical gas and becomes a degenerate gas, it is possible that the central temperature may pass through a maximum and that the star may cool down and die. This possibility has already been illustrated for low mass stars in figs. 76 and 86 Such a dying star is likely to have a low luminosity. It is also likely to have a high density. It can only begin to cool down after its central regions have become degenerate and, if the central temperature has previously risen sufficiently for one or more sets of energy-releasing nuclear reactions to occur, a very high density is necessary before degeneracy can occur, as has been seen in Chapter 4 (fig. 45)

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars — compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.

Almost every galaxy has a supermassive black hole (SMBH) residing at its center, the Milky Way included. Recent studies suggest that these unique places are expected to host a high abundance of stellar and compact object binaries. These binaries form hierarchical triple systems with the SMBH and undergo the eccentric Kozai–Lidov (EKL) mechanism. Here we estimate the detectability of potential gravitational-wave emission from these compact objects within the frequency band of the Laser Interferometer Space Antenna (LISA) and Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors. We generate a post-EKL population of stars at the onset of Roche limit crossing and follow their evolution to compact object binaries. As a proof of concept, we adopt two metallicities, solar metallicity (Z = 0.02) and 15% of it (Z = 0.003). We demonstrate that over the observation timescale of LISA, black hole (BH) binaries (BH–BH) and white dwarf (WD) binaries provide the most prominent GW sources via the EKL-assisted merger channel. Systems involving neutron stars (NSs) are less observable but possibly abundant through different merger channels. Our population synthesis of BH–BH with Z = 0.02 (Z = 0.003) translates to ∼4 (24) events per year with LIGO within a 1 Gpc3 sphere. We also estimated the number of binaries visible in the LISA band within the inner parsec of our Galactic center (and possibly other galaxies) to be about 14–150 WD–WD, 0–2 NS–BH, 0.2–4 NS–NS, and 0.3–20 BH–BH.

As soon as the theory of general relativity was propounded, astronomers and physicists made ready to test its observational predictions. There was of course the excess motion of the perihelion of the orbit of Mercury, which the theory had been designed in part to explain. There was the gravitational bending of light beams (verified at the eclipse of 1919), the gravitational redshifting of light and the gravitational retarding of light (both verified in recent years). Light rays and the planet Mercury would exist without the theory of general relativity. Its effects on their behavior are small. But there is a class of objects whose existence is predicted by general relativity and which do not exist if the theory in some form is not true. These are the black holes, objects that have collapsed under the influence of their own gravitation until they are so dense and have such strong gravitational fields that neither matter nor radiation can escape from their surfaces. To a general relativist a black hole is an example of extremely curved space. In and around it the effects of general relativity are not minor; they are dominant, and they determine the nature of the phenomena that occur. The discovery of an actual black hole would provide an astrophysical working place for general relativity, a region where the effects of space curvature could be studied readily rather than having to be sorted out as tiny corrections to the nearly flat space that surrounds ordinary objects. As Remo J. Ruffini of Princeton University puts it, the discovery of a black hole would be for general relativity what the discovery of the photon (also, by the way, associated with Einstein) was for quantum theory and the physics of the microcosm. Ruffini believes, and has believed for more than a year, that at least one black hole is currently under observation (SN: 1/13/73, p. 28). Controversy rages, and to the discussion Ruffini now brings theoretical arguments and observational evidence, some of which was barely analyzed in time for him to use it at the meeting of the American Physical Society two weeks ago in Chicago. Ruffini's candidate for a black hole is Cygnus X-1, one of a newly discovered class of celestial X-ray sources, X-ray binaries. Up to, a point there is general agreement as to what these binary sources are: They are systems in which a more or less normal star is gravitationally bound to a highly condensed dark companion. The usual explanation as to how the companion got condensed is that it is the last stage of stellar evolution, what is left over after a supernova explosion. Matter streams out from the normal star and falls onto the dark companion. The streaming matter forms a rotating disk around the dark companion in which pieces of matter gradually spiral inward until they fall on the dark companion. As they do so they convert energy they gain through their fall to X-rays. (The matter in the disks is electrically charged ionized plasma, not neutral gas, so it has means to do this.) The argument starts over the nature of the condensed body. The main candidates are black holes and neutron stars-though a few observers may hold out for white dwarfs. To make the case for black holes or for a black hole one needs a way of distinguishing observationally between the two. Ruffini provides a way. It has to do with magnetic fields. Stars have magnetic fields. When they collapse, even through the violence of a supernova explosion, they should retain those fields. Thus neutron stars and black holes can have magnetic fields. But in the configuration of those fields lies the difference. A neutron star

With the launch of the Wide-field Infrared Survey Explorer (WISE), a new era of detecting planetary debris and brown dwarfs (BDs) around white dwarfs (WDs) has begun with the WISE InfraRed Excesses around Degenerates (WIRED) Survey. The WIRED Survey is sensitive to substellar objects and dusty debris around WDs out to distances exceeding 100 pc, well beyond the completeness level of local WDs. In this paper, we present a cross-correlation of the preliminary Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) WD catalog between the WISE, Two-Micron All Sky Survey (2MASS), UKIRT Infrared Deep Sky Survey (UKIDSS), and SDSS DR7 photometric catalogs. From ~18,000 input targets, there are WISE detections comprising 344 "naked" WDs (detection of the WD photosphere only), 1020 candidate WD+M dwarf binaries, 42 candidate WD+BD systems, 52 candidate WD+dust disk systems, and 69 targets with indeterminate infrared excess. We classified all of the detected targets through spectral energy distribution model fitting of the merged optical, near-IR, and WISE photometry. Some of these detections could be the result of contaminating sources within the large (≈6'') WISE point-spread function; we make a preliminary estimate for the rates of contamination for our WD+BD and WD+disk candidates and provide notes for each target of interest. Each candidate presented here should be confirmed with higher angular resolution infrared imaging or infrared spectroscopy. We also present an overview of the observational characteristics of the detected WDs in the WISE photometric bands, including the relative frequencies of candidate WD+M, WD+BD, and WD+disk systems.

Electron–positron pairs in physics and astrophysics: From heavy nuclei to black holes

The universal link between the processes of accretion and ejection leads to the formation of jets and outflows around accreting compact objects. Incoherent s ynchrotron emission from these outflows can be observed from a wide range of accreting binaries, including black holes, neutron stars, and white dwarfs. Monitoring the evolution of the radio emission during their sporadic outbursts provides important insights into the launching o f jets, and, when coupled with the behaviour of the source at shorter wavelengths, probes the underlying connection with the accretion process. Radio observations can also probe the impact of jets/outflows (including other explosive events such as magnetar giant flares) on the ambient medium, q uantifying their kinetic feedback. The high sensitivity of the SKA will open up new parameter space, enabling the monitoring of accreting stellar-mass compact objects from their bright, Eddington-limited outburst states down to the lowest-luminosity quiescent levels, whose intrinsic faintness has to date precluded detailed studies. A census of quiescently accreting black h oles will also constrain binary evolution processes. By enabling us to extend our existing investigations of black hole jets to the fainter jets from neutron star and white dwarf systems, the SKA will permit comparative studies to determine the role of the compact object in jet formation. The high sensitivity, wide field of view and multibeaming capability of the SKA will enable the detection and monitoring of all bright flaring transients in the observable local Universe (within ∼ 15 Mpc), including the radio counterparts of ultraluminous X-ray sources, improving our understanding of accretion and jet ejection at the highest rates, with important implications for the growth of the first quasars. As synchrotron events peak earlier at higher frequencies, and with higher flux densities, such studies will be best enabled by SKA1-MID, in the higher-frequency bands 4 and 5. With the high sensitivity available from SKA1-MID, we will also be able to probe isolated quiescent black holes undergoing Bondi-Hoyle accretion from the nearby environment, both stellar-mass black holes in the field and the putative population of intermediat e black holes in globular clusters. This chapter reviews the science goals outlined above, demonstrating the progress that will be made by the SKA in studying incoherent synchrotron emission from accreting compact objects. We also discuss the potential of the astrometric and imaging observations that would be possible should a significant VLBI component be included in phase 1 (and eventu ally phase 2) of the SKA.

We study the nature of phase transitions between gaseous and condensed states in the self-gravitating Fermi gas at finite temperature in general relativity. The condensed states can represent compact objects such as white dwarfs, neutron stars, or dark matter fermion balls. The caloric curves depend on two parameters: the system size R and the particle number N. When N < NOV, where NOV is the Oppenheimer–Volkoff limit, there exists an equilibrium state for any value of the temperature T and energy E as in the nonrelativistic case [P.H. Chavanis, Int. J. Mod. Phys. B 20, 3113 (2006)]. Gravitational collapse is prevented by quantum mechanics (Pauli’s exclusion principle). When N > NOV, there is no equilibrium state below a critical energy and below a critical temperature. In that case, the system is expected to collapse toward a black hole. We plot the caloric curves of the general relativistic Fermi gas, study the different types of phase transitions that occur in the system, and determine the phase diagram in the (R, N) plane. The nonrelativistic results are recovered for N ≪ NOV and R ≫ ROV with NR3 fixed. The classical (non quantum) results are recovered for N ≫ NOV and R ≫ ROV with N∕R fixed. We discuss the commutation of the limits c → +∞ and ℏ → 0. We study the relativistic corrections to the nonrelativistic caloric curves and the quantum corrections to the classical caloric curves. We highlight a situation of physical interest where a self-gravitating Fermi gas, by cooling, first undergoes a phase transition toward a compact object (white dwarf, neutron star, dark matter fermion ball), then collapses into a black hole. This situation occurs in the microcanonical ensemble when NOV < N < 3.73 NOV. We also relate the phase transitions from a gaseous state to a core-halo state in the microcanonical ensemble to the onset of red-giant structure and to the supernova phenomenon.

Neutron stars and stellar-mass black holes are the remnants of massive stars, which ended their lives in supernova explosions. These exotic objects can only be studied in relatively rare cases. If they are interacting with close companions they become bright X-ray sources. If they are neutron stars, they may be detected as pulsars. Only a few hundred such systems are presently known in the Galaxy. However, there should be many more binaries with basically invisible compact objects in non-interacting binaries.Here we report the discovery of unseen compact companions to hot subdwarfs in close binary systems. Hot subdwarfs are evolved helium-core-burning stars that have lost most of their hydrogen envelopes, often due to binary interactions. Using high-resolution spectra and assuming tidal synchronisation of the subdwarfs, we were able to constrain the companion masses of 31 binaries. While most hot subdwarf binaries have white-dwarf or late-type main sequence companions, as predicted by binary evolution models, at least 5% of the observed subdwarfs must have very massive companions: unusually heavy white dwarfs, neutron stars and, in some cases, even black holes. We present evolutionary models which show that such binaries can indeed form if the system has evolved through two common-envelope phases. This new connection between hot subdwarfs, which are numerous in the Galaxy, and massive compact objects may lead to a tremendous increase in the number of known neutron stars and black holes and shed some light on this dark population and its evolutionary link to the X-ray binary population.

We review the lives, deaths and nucleosynthetic signatures of intermediate-mass stars in the range ≈6–12 M⊙, which form super-AGB stars near the end of their lives. The critical mass boundaries both between different types of massive white dwarfs (CO, CO–Ne, ONe), and between white dwarfs and supernovae, are examined along with the relative fraction of super-AGB stars that end life either as an ONe white dwarf or as a neutron star (or an ONeFe white dwarf), after undergoing an electron capture supernova event. The contribution of the other potential single-star channel to electron-capture supernovae, that of the failed massive stars, is also discussed. The factors that influence these different final fates and mass limits, such as composition, rotation, the efficiency of convection, the nuclear reaction rates, mass-loss rates, and third dredge-up efficiency, are described. We stress the importance of the binary evolution channels for producing electron-capture supernovae. Recent nucleosynthesis calculations and elemental yield results are discussed and a new set of s-process heavy element yields is presented. The contribution of super-AGB star nucleosynthesis is assessed within a Galactic perspective, and the (super-)AGB scenario is considered in the context of the multiple stellar populations seen in globular clusters. A brief summary of recent works on dust production is included. Last, we conclude with a discussion of the observational constraints and potential future advances for study into these stars on the low mass/high mass star boundary.

The Mystery of the Cosmic Gamma-Ray Zaps