Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “NEUTRON STARS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Radio emission from binary stars

Radio emission from binary star systems; characteristics of the binary systems inferred from the radio observations; and the reasons for the activity are reviewed. Binary stars with two main sequence stars, with one normal star and a white dwarf, and those containing a neutron star or a black hole are described. Energy may be directly available as matter falls into the potential well of a compact object. Electromagnetic induction effects may occur due to relative motions of magnetic fields and matter. By enforcing rapid rotation, binaries can induce strong dynamo action and hence generate free energy in the form of intense, complex, evolving magnetic fields. Whatever the source of energy, the observations at radio and X-ray wavelengths demonstrate that electrons are accelerated to high energies (mildly relativistic and, ultrarelativistic). Observed or inferred radio brightness temperatures range up to 10 to the 15th power K or more, implying coherent emission for sources brighter than 10 billion K.

Dulk, George A.↗
NASA NTRS1986

Radio emission from binary stars

This paper reviews the radio emission from binary star systems - the emission processes that occur, the characteristics of the binary systems inferred from the radio observations, and the reasons for the activity. Several classes of binary stars are described including those with two main sequence stars, those with one normal star and a white dwarf, and those containing a neutron star or a black hole.

Dulk, G. A.↗
NASA NTRS1990

Interacting nuclei in distant galaxies

The N-galaxy 3C 390.3 has been monitored spectroscopically since 1974 (Osterbrock, Koski and Phillips 1975; Oke 1988). From various archives and literature, it is found that the Balmer lines change their intensities and profiles in a dramatic manner. The H alpha profile is very broad and peculiar, and the relative intensities of its two humps changes consistently with time, possibly periodically. Before 1980, the blue hump was significantly stronger than the one in the red. From 1980 to 1983 the blue hump became stronger (see Oke 1988). After 1983 the H alpha profile has returned to its early shape and seems to have completed a full circle. Unlike the rapid (on the order of a month or even less) and aperiodic variation in the continuum and integrated line intensities, the change in broad profile seems slow and consistent. Taking the analogy of cataclysmic variables, the double-horn profiles have been observed in cases of interacting stars. For example, the emission lines, both in He II and hydrogen Balmer lines in GD 552 (Stover 1985) show double-horn profiles and periodical changes in their line profiles, including the change in ratios of two humps. It is understood that the D-wave components (Smak 1976) are the signature of an emitting disk and the S-wave component is from the emission at a hot spot which rotates and results in a moving component in the velocity space. The mass flow from the nearby interacting star provides the stream toward the core of a neutron star or white dwarf. Therefore, it is proposed that the variation of broad line profiles observed in 3C 390.3 may be the result of a pair of interacting massive cores. The rotational velocity dominates and produces a variable double-horn profile. However, the line widths observed in broad line radio galaxies are one order larger than that in interacting stars. The Balmer decrements imply a much smaller density (10(exp 10-12) cm(exp-3)) than that in the cataclysmic variables. The much larger velocity and much thinner density make it unlikely that the broad line emission is simply formed in an accretion disk. The authors postulate that a significant rotational motion is involved. If the observed squared profiles are indeed due to the rotational velocity field, one can naturally explain their rare occurrence.

Zheng, Wei↗
NASA NTRS1991

Frontiers of stellar evolution

The present conference discusses theoretical and observational views of star formation, spectroscopic constraints on the evolution of massive stars, very low mass stars and brown dwarfs, asteroseismology, globular clusters as tests of stellar evolution, observational tests of stellar evolution, and mass loss from cool evolved giant stars. Also discussed are white dwarfs and hot subdwarfs, neutron stars and black holes, supernovae from single stars, close binaries with evolved components, accretion disks in interacting binaries, supernovae in binary systems, stellar evolution and galactic chemical evolution, and interacting binaries containing compact components.

Lambert, David L.↗
NASA NTRS1995

The Dripping Handrail Model: Transient Chaos in Accretion Systems

We define and study a simple dynamical model for accretion systems, the "dripping handrail" (DHR). The time evolution of this spatially extended system is a mixture of periodic and apparently random (but actually deterministic) behavior. The nature of this mixture depends on the values of its physical parameters - the accretion rate, diffusion coefficient, and density threshold. The aperiodic component is a special kind of deterministic chaos called transient chaos. The model can simultaneously exhibit both the quasiperiodic oscillations (QPO) and very low frequency noise (VLFN) that characterize the power spectra of fluctuations of several classes of accretion systems in astronomy. For this reason, our model may be relevant to many such astrophysical systems, including binary stars with accretion onto a compact object - white dwarf, neutron star, or black hole - as well as active galactic nuclei. We describe the systematics of the DHR's temporal behavior, by exploring its physical parameter space using several diagnostics: power spectra, wavelet "scalegrams," and Lyapunov exponents. In addition, we note that for large accretion rates the DHR has periodic modes; the effective pulse shapes for these modes - evaluated by folding the time series at the known period - bear a resemblance to the similarly- determined shapes for some x-ray pulsars. The pulsing observed in some of these systems may be such periodic-mode accretion, and not due to pure rotation as in the standard pulsar model.

Young, Karl↗
NASA NTRS2007

Gamma-Ray Bursts in the Swift Era

GRB research has undergone a revolution in the last two years. The launch of Swift, with its rapid slewing capability, has greatly increased the number and quality of GRB localizations and X-ray and optical afterglow lightcurves. Over 160 GRBs have been detected, and nearly all that have been followed up with the on-board narrow field telescopes. Advances in our understanding of short GRBs have been spectacular. The detection of X-ray afterglows has led to accurate localizations from ground based observatories, which have given host identifications and redshifts. Theoretical models for short GRB progenitors have, for the first time, been placed on a sound foundation. The hosts for the short GRBs differ in a fundamental way from the long GRB hosts: short GRBs tend to occur in non-star forming galaxies or regions, whereas long GRBs are strongly concentrated within star forming regions. Observations are consistent with a binary neutron star merger model, but other models involving old stellar populations are also viable. Swift has greatly increased the redshift range of GRB detection. The highest redshift GRBs, at zeta approx. 5-6, are approaching the era of reionization. Ground-based deep optical spectroscopy of high redshift bursts is giving metallicity measurements and other information on the source environment to much greater distance than other techniques. The localization of GRB 060218 to a nearby galaxy, and association with SN 2006aj, added a valuable member to the class of GRBs with detected supernova. The prospects for future progress are excellent given the >10 year orbital lifetime of the Swift satellite.

Gehrels, Neil↗
NASA NTRS2024

The Role of a Neutron Component in the Photospheric Emission of Long Duration Gamma-Ray Burst Jets

Long-duration gamma-ray bursts (LGRBs), thought to be produced during core-collapse supernovæ, may have a prominent neutron component in the outflow material. If present, neutrons can change how photons scatter in the outflow by reducing its opacity, thereby allowing the photons to decouple sooner than if there were no neutrons present. Understanding the details of this process could therefore allow us to probe the central engine of LGRBs, which is otherwise hidden. Here, we present results of the photospheric emission from an LGRB jet, using a combination of relativistic hydrodynamic simulations and radiative transfer post-processing using the Monte Carlo Radiation Transfer (MCRaT) code. We control the size of the neutron component in the jet material by varying the equilibrium electron fraction Y e , and we find that the presence of neutrons in the GRB fireball affects the Band parameters α and E 0 , while the picture with the β parameter is less clear. In particular, the break energy E 0 is shifted to higher energies. Additionally, we find that increasing the size of the neutron component also increases the total radiated energy of the outflow across multiple viewing angles. Our results not only shed light on LGRBs, but are also relevant to short-duration gamma-ray bursts associated with binary neutron star mergers, due to the likelihood of a prominent neutron component in such systems.

Gamma-ray bursts↗
NASA NTRS1975

Do comets play a role in galactic chemistry and gamma-ray bursts

This paper explores the plausibility of the assumption that enough material from interstellar space is locked up in comets to reduce significantly the apparent growth rate of 'heavy' elements (mass greater than He) and, therefore, the present abundance of heavy elements in the interstellar medium and in the disk stars. A related suggestion concerns the influx of comets on neutron stars as a source of gamma-ray bursts. Although no interstellar comets have been observed, reasonable upper limits to the observed numbers and masses do not rule out the first suggestion. The gamma-ray-burst suggestion appears unlikely. A surprisingly large total mass of comets could be gravitationally bound to the sun and, of course, to other stars, but remain undetected. The nature of the 1908 Tunguska explosion is discussed briefly. It was probably not an encounter with an active comet.

Whipple, F. L.↗
NASA NTRS1986

Stellar activity at radio wavelengths

Hundreds of stars have now been detected at radio wavelengths. At least four processes are believed to cause the radio emission: thermal bremsstrahlung, gyrosynchrotron, cyclotron maser, and plasma radiation. Here the characteristics of the various classes of detected stars are reviewed, along with the putative reasons for the radio emission. The classes of stars described include: single stars, binaries containing two main sequences and/or giant stars, binaries containing one white dwarf, and binaries containing one neutron star or black hole.

Dulk, George A.↗
NASA NTRS1981

Evolution of X-ray astronomy

The development of X-ray astronomy, stopping short of recent observations by grazing incidence telescope, is surveyed. The discovery in 1962 of an extrasolar X-ray source, Sco X-1, with orders of magnitude stronger than astronomers believed might exist is recounted. It turned out to belong to a class of previously unknown galactic objects, the X-ray stars. The identification of a strong X-ray source with the Crab Nebula and the identification of Sco X-1 with a faint, peculiar optical object soon followed. The demonstration that X-ray stars are binary systems, each consisting of a collapsed object (a neutron star, occasionally a black hole) accreting matter from an ordinary star, and the discovery of X-ray bursts are further milestones. The discovery of exceedingly strong X-ray emission from active galaxies, quasars and clusters of galaxies and the demonstration that in these the principal X-ray source is a hot gas filling the space between galaxies sum up results.

Rossi, B.↗
NASA NTRS1989

Windows on the axion

Peccei-Quinn symmetry with attendant axion is a most compelling, and perhaps the most minimal, extension of the standard model, as it provides a very elegant solution to the nagging strong CP-problem associated with the theta vacuum structure of QCD. However, particle physics gives little guidance as to the axion mass; a priori, the plausible values span the range: 10(-12)eV is approx. less than m(a) which is approx. less than 10(6)eV, some 18 orders-of-magnitude. Laboratory experiments have excluded masses greater than 10(4)eV, leaving unprobed some 16 orders-of-magnitude. Axions have a host of interesting astrophysical and cosmological effects, including, modifying the evolution of stars of all types (our sun, red giants, white dwarfs, and neutron stars), contributing significantly to the mass density of the Universe today, and producting detectable line radiation through the decays of relic axions. Consideration of these effects has probed 14 orders-of-magnitude in axion mass, and has left open only two windows for further exploration: 10(-6)eV is approx. less than m(a) is approx. less than 10(-3)eV and 1eV is approx. less than m(a) is approx. less than 5eV (hadronic axions only). Both these windows are accessible to experiment, and a variety of very interesting experiments, all of which involve heavenly axions, are being planned or are underway.

Turner, Michael S.↗
NASA NTRS1977

Exploding stars, pulsars and black holes in space

Brief factual reviews are provided for supernovae, pulsars and neutron stars, and black holes. Also discussed in general terms are red giants, white dwarfs, quasars and radio galaxies.

Panagakos, N.↗
NASA NTRS1975

Electromagnetic pulse from supernovae

Upper and lower limits to the radiated electromagnetic pulse from a supernova are calculated assuming that the mass fraction of the matter expanding inside the dipole magnetic field shares energy and maintains the pressure balance in the process. A supernova model is described in which the explosion occurs in old low-mass stars containing less than 10% hydrogen in their ejecta and a remnant neutron star is produced. The analysis indicates that although the surface layer of a star of 1 g/cu thickness may be shock-accelerated to an energy factor of about 100 and may expand into the vacuum with an energy factor approaching 10,000, the equatorial magnetic field will retard this expansion so that the inner, more massive ejecta layers will effectively accelerate the presumed canonical dipole magnetic field to greater velocities than would the surface layer alone. A pulse of 10 to the 46th power ergs in a width of about 150 cm will result which will not be affected by circumstellar matter or electron self-radiation effects. It is shown that interstellar matter will attenuate the pulse, but that charge separation may reduce the attenuation and allow a larger pulse to escape.

Colgate, S. A.↗
NASA NTRS1991

Cold equation of state in a strong magnetic field - Effects of inverse beta-decay

The influence of a high magnetic field (B is greater than 10 exp 12 G) on the degenerate matter equation of state appropriate to a neutron star is studied. The regime dominated by relativistic electrons up to the neutron drip density is highlighted. The equilibrium matter composition and equation of state, allowing for inverse beta-decay. Two different equilibrium models are determined: an ideal neutron-proton-electron (npe) gas and the more realistic model of Baym, Pethick, and Sutherland (1971) consisting of a Coulomb lattice of heavy nuclei embedded in an electron gas. For a sufficiently high field strength, the magnetic field has an appreciable effect, changing the adiabatic index of the matter and the nuclear transition densities. The influence of a strong field on some simple nonequilibrium processes, including beta-decay and inverse beta-decay (electron capture) is also considered. The effects produced by the magnetic field are mainly due to the changes in the transverse electron quantum orbits and the allowed electron phase space induced by the field.

Lai, Dong↗
NASA NTRS2008

Gamma Ray Burst Discoveries with the Swift Mission

Gamma-ray bursts (GRBs) are among the most fascinating occurrences in the universe. They are powerful explosions, visible to high redshift, and thought to be the signature of black hole formation. The Swift Observatory has been detecting 100 bursts per year for 3 years and has greatly stimulated the field with new findings. Observations are made of the X-ray and optical afterglow from approximately 1 minute after the burst, continuing for days. Evidence is building that the long and short duration subcategories of GRBs have very different origins: massive star core collapse to a black hole for long bursts and binary neutron star coalescence to a black hole for short bursts. The similarity to Type II and Ia supernovae originating from young and old stellar progenitors is striking. Bursts are providing a new tool to study the high redshift universe. Swift has detected several events at z greater than 5 and one at z=6.3 giving metallicity measurements and other data on galaxies at previously inaccessible distances. The talk will present the latest results from Swift in GRB astronomy.

Gehrels, Neil↗
NASA NTRS2008

Gamma Ray Burst Discoveries with the Swift Mission

Gamma-ray bursts (GRBs) are among the most fascinating occurrences in the universe. They are powerful explosions, visible to high redshift, and thought to be the signature of black hole formation. The Swift Observatory has been detecting 100 bursts per year for 3 years and has greatly stimulated the field with new findings. Observations are made of the X-ray and optical afterglow from - 1 minute after the burst, continuing for days. Evidence is building that the long and short duration subcategories of GRBs have very different origins: massive star core collapse to a black hole for long bursts and binary neutron star coalescence to a black hole for short bursts. The similarity to Type I1 and Ia supernovae originating from young and old stellar progenitors is striking. Bursts are providing a new tool to study the high redshift universe. Swift has detected several events at z>5 and one at z=6.3 giving metallicity measurements and other data on galaxies at previously inaccessible distances. The talk will present the latest results from Swift in GRB astronomy.

Gehrels, Neil↗
NASA NTRS2009

Gamma Ray Burst Discoveries with the Swift Mission

Gamma-ray bursts (GRBs) are among the most fascinating occurrences in the universe. They are powerful explosions, visible to high redshift, and thought to be the signature of black hole formation. The Swift Observatory has been detecting 100 bursts per year for 4 years and has greatly stimulated the field with new findings. Observations are made of the X-ray and optical afterglow from approximately 1 minute after the burst, continuing for days. Evidence is building that the long and short duration subcategories of GRBs have very different origins: massive star core collapse to a black hole for long bursts and binary neutron star coalescence to a black hole for short bursts. The similarity to Type II and Ia supernovae originating from young and old stellar progenitors is striking. Bursts are providing a new tool to study the high redshift universe. Swift has detected several events at z>5 and one at z=6.7 giving metallicity measurements and other data on galaxies at previously inaccessible distances. The talk will present the latest results from Swift in GRB astronomy.

Gehrels, Neil↗
NASA NTRS2009

Gamma Ray Bursts and the Birth of Black Holes

Black holes have been predicted since the 1940's from solutions of Einstein's general relativity field equation. There is strong evidence of their existence from astronomical observations, but their origin has remained an open question of great interest. Gamma-ray bursts may the clue. They are powerful explosions, visible to high redshift, and appear to be the birth cries of black holes. The Swift and Fermi missions are two powerful NASA observatories currently in orbit that are discovering how gamma-ray bursts work. Evidence is building that the long and short duration subcategories of GRBs have very different origins: massive star core collapse to a black hole for long bursts and binary neutron star coalescence to a black hole for short bursts. The similarity to Type II and Ia supernovae originating from young and old stellar progenitors is striking. Bursts are tremendously luminous and are providing a new tool to study the high redshift universe. One Swift burst at z=8.3 is the most distant object known in the universe. The talk will present the latest gamma-ray burst results from Swift and Fermi and will highlight what they are teaching us about black holes and jet outflows.

Gehrels, Neil↗