Nir J. Shaviv

Nir J. Shaviv
Hebrew University of Jerusalem | HUJI · Racah Institute of Physics

PhD

About

143
Publications
14,018
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4,377
Citations
Citations since 2017
14 Research Items
1556 Citations
2017201820192020202120222023050100150200250300
2017201820192020202120222023050100150200250300
2017201820192020202120222023050100150200250300
2017201820192020202120222023050100150200250300

Publications

Publications (143)
Article
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We review the long-term climate variations during the last 540 million years (Phanerozoic Eon). We begin with a short summary of the relevant geological and geochemical datasets available for the reconstruction of long-term climate variations. We then explore the main drivers of climate that appear to explain a large fraction of these climatic osci...
Article
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Experiments on sulphuric acid nucleation in low oxygen atmospheres were done in order to investigate the role of nucleation in the Archean atmosphere. Nu-cleation initiated by photolysis of SO2 and subsequent reaction between atomic O and SO2 was measured with a PSM and a separate CPC. The parameters were <10 ppm O2 with varying levels of SO2 (4 le...
Article
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Atmospheric ionization produced by cosmic rays has been suspected to influence aerosols and clouds, but its actual importance has been questioned. If changes in atmospheric ionization have a substantial impact on clouds, one would expect to observe significant responses in Earth’s energy budget. Here it is shown that the average of the five stronge...
Article
Interaction-powered supernovae (SNe) explode within an optically thick circumstellar medium (CSM) that could be ejected during eruptive events. To identify and characterize such pre-explosion outbursts, we produce forced-photometry light curves for 196 interacting SNe, mostly of Type IIn, detected by the Zwicky Transient Facility between early 2018...
Preprint
Interaction-powered supernovae (SNe) explode within an optically-thick circumstellar medium (CSM) that could be ejected during eruptive events. To identify and characterize such pre-explosion outbursts we produce forced-photometry light curves for 196 interacting SNe, mostly of Type IIn, detected by the Zwicky Transient Facility between early 2018...
Article
Full-text available
Abstract The presence of small ions influences the growth dynamics of a size distribution of aerosols. Specifically, the often neglected mass of small ions influences the aerosol growth rate, which may be important for terrestrial cloud formation. To this end, we develop the Ion and Charged Aerosol Growth Enhancement (ION‐CAGE) code, a numerical mo...
Preprint
The presence of small ions influences the growth dynamics of a size distribution of aerosols. Specifically the often neglected mass of small ions influences the aerosol growth rate, which may be important for terrestrial cloud formation. To this end, we develop a numerical model to calculate the growth of a species of aerosols in the presence of ch...
Article
We have previously focused on studying the electron-capture isotopes within the dynamic spiral-arms cosmic-rays propagation model and empirically derived the energy dependence of the electron attachment rate using the observation of ⁴⁹Ti/⁴⁹V and ⁵¹V/⁵¹Cr ratios in cosmic rays. We have also shown how this relation recovers the energy dependence seen...
Article
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Ions produced by cosmic rays have been thought to influence aerosols and clouds. In this study, the effect of ionization on the growth of aerosols into cloud condensation nuclei is investigated theoretically and experimentally. We show that the mass-flux of small ions can constitute an important addition to the growth caused by condensation of neut...
Article
We have previously focused on studying the electron-capture isotopes within the dynamic spiral-arms model and empirically derived the energy dependence of the electron attachment rate using the observation of $^{49}$Ti/$^{49}$V and $^{51}$V/$^{51}$Cr ratios in cosmic rays (Benyamin et al. 2017). We have also shown how this relation recovers the ene...
Article
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Every supernova hitherto observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower moving material that was previously hidden. In addition, every supernova that exhibits the ab...
Article
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Electron capture (EC) isotopes are known to provide constraints on the low energy behavior of cosmic rays (CRs), such as re-acceleration. Here we study the EC isotopes within the framework of the dynamic spiral-arms CR propagation model in which most of the CR sources reside in the galactic spiral arms. The model was previously used to explain the...
Article
Most of the diffuse Galactic GeV gamma-ray emission is produced via collisions of cosmic ray (CR) protons with ISM protons. As such the observed spectra of the gamma-rays and the CRs should be strongly linked. Recent observations of Fermi-LAT exhibit a hardening of the gamma-ray spectrum at around a hundred GeV, between the Sagittarius and Carina t...
Article
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A method is developed to rank Forbush Decreases (FDs) in the galactic cosmic ray radiation according to their expected impact on the ionization of the lower atmosphere. Then a Monte Carlo bootstrap based statistical test is formulated to estimate the significance of the apparent response in physical and micro-physical cloud parameters to FDs. The t...
Article
The detection by Rest et al. (2012) of light echoes from η Carinae has provided important new observational constraints on the nature of its 1840’s era giant eruption. Spectra of the echoes suggest a relatively cool spectral temperature of about 5500K, lower than the lower limit of about 7000K suggested in the optically thick wind outflow analysis...
Article
Using a recent geochemical reconstruction of the Phanerozoic climate which exhibits a 32 Ma oscillation with a phase and the secondary modulation expected from the vertical the motion of the solar system perpendicular to the galactic plane (shaviv et al. 2014), we show that a kinematically cold strongly interacting disk dark matter (dDM) component...
Article
We analyze the motion of stars in the direction perpendicular to the galactic plane following a spiral arm passage. We show that the fast change in the vertical galactic potential causes a thermalized distribution to develop a distinctive "ringing"-like non-thermal signature. We use A and F-stars from the extended Hipparocos catalogue to show that...
Article
The progenitors of some supernovae (SNe) exhibit outbursts with super-Eddington luminosities prior to their final explosions. This behavior is common among Type IIn SNe, but the driving mechanisms of these precursors are not yet well understood. SNHunt 275 was announced as a possible new SN during May 2015. Here we report on pre-explosion observati...
Article
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The Boron to Carbon (B/C) and sub-Fe/Fe ratios provides an important clue on Cosmic Ray (CR) propagation within the Galaxy. These ratios estimate the grammage that the CR path as they propagate from their sources to Earth. Attempts to explain these ratios within the standard CR propagation models require ad hoc modifications and even with those the...
Article
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The progenitor stars of several Type IIb supernovae (SNe) show indications for extended hydrogen envelopes. These envelopes might be the outcome of luminous energetic pre-explosion events, so-called precursor eruptions. We use the Palomar Transient Factory (PTF) pre-explosion observations of a sample of 27 nearby Type IIb SNe to look for such precu...
Article
Stars with a different vertical motion relative to the galactic disk have a different average acceleration. According to Modified Newtonian Dynamics (MOND) theories they should therefore have a different average orbital velocity while revolving around the Milky Way. We show that this property can be used to constrain MOND theories by studying stars...
Article
With satellite altimetry data accumulating over the past two decades, the mean sea level (MSL) can now be measured to unprecedented accuracy. We search for physical processes which can explain the sea level variations and find that at least 70% of the variance in the annually smoothed detrended altimetry data can be explained as the combined effect...
Article
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We present analytical solutions to the steady state injection-condensation-coagulation equation of aerosols in the atmosphere. These solutions are appropriate under different limits but more general than previously derived analytical solutions. For example, we provide an analytic solution to the coagulation limit plus a condensation correction. Our...
Article
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One of the most interesting problems in Cataclysmic Variables is the long time scale evolution. This problem appears in long time evolution, which is also very important in the search for the progenitor of SN Ia. The classical approach to overcome this problem in the simulation of novae evolution is to assume: (1) A constant in time, rate of mass t...
Article
We suggest several ideas which when combined could lead to a new mechanism for long-term pulsations of very hot and luminous stars. These involve the interplay between convection, radiation, atmospheric clumping and winds, which collectively feed back to stellar expansion and contraction. We discuss these ideas and point out the future work require...
Article
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We describe a new code to simulate the stellar evolution of a close interacting binary system. It is then used to calculate the evolution of a classical nova system composed of a 1.25 Msun Main-Sequence (MS) star and a 1.0 Msun white dwarf (WD) companion. The system begins as a well separated non-interacting binary system. Initially, the two stars...
Article
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A new δ(18)O Phanerozoic database, based on 24,000 low-Mg calcitic fossil shells, yields a prominent 32 Ma oscillation with a secondary 175 Ma frequency modulation. The periodicities and phases of these oscillations are consistent with parameters postulated for the vertical motion of the solar system across the galactic plane, modulated by the radi...
Article
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There is a growing number of supernovae (SNe), mainly of Type IIn, which present an outburst prior to their presumably final explosion. These precursors may affect the SN display, and are likely related to some poorly charted phenomena in the final stages of stellar evolution. Here we present a sample of 16 SNe IIn for which we have Palomar Transie...
Article
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We present a radiative transfer model for Earth-Like-Planets (ELP). The model allows the assessment of the effect of a change in the concentration of an atmospheric component, especially a greenhouse gas (GHG), on the surface temperature of a planet. The model is based on the separation between the contribution of the short wavelength molecular abs...
Article
We present a radiative transfer model for Earth-Like-Planets (ELP). The model allows the assessment of the effect of a change in the concentration of an atmospheric component, especially a greenhouse gas (GHG), on the surface temperature of a planet. The model is based on the separation between the contribution of the short wavelength molecular abs...
Article
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We construct a Galactic cosmic ray (CR) diusion model while considering that CR sources reside predominantly in the Galactic spiral arms. We nd that the CR ux (CRF) reaching the solar system should periodically increase each crossing of a Galactic spiral arm. We search for this signal in the CR exposure age record of Iron meteorites and conrm this...
Article
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We develop a fully three dimensional numerical code describing the diffusion of cosmic rays in the Milky Way. It includes the nuclear spallation chain up to Oxygen, and allows the study of various cosmic ray properties, such as the CR age, grammage traversed, and the ratio between secondary and primary particles. This code enables us to explore a m...
Article
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The binary pulsar J0737−3039 is the only known system having two observable pulsars, thus offering a unique laboratory to test general relativity and explore pulsar physics. Based on the low eccentricity and the position within the galactic plane, two of us have argued that pulsar B had a non-standard formation scenario with little or no mass eject...
Article
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Turbulent processes in the convective envelopes of the Sun and stars have been shown to be a source of internal acoustic excitations. In single stars, acoustic waves having frequencies below a certain cut-off frequency propagate nearly adiabatically and are effectively trapped below the photosphere where they are internally reflected. This reflecti...
Chapter
It is generally tacitly assumed that the atmosphere of a habitable planet absorbs in the infrared and is transparent in the visible. We consider the cases in which the optical depth in the visible is not negligible. We show that such planets can harbor life under conditions similar to those found on Earth. Moreover, it is conceivable that planetary...
Article
Solar variations appear to have a significant effect on climate. I will begin by reviewing the evidence pointing to a large solar/climate link and present measurements quantifying it. I will then discuss the atmospheric effects of cosmic rays, which offer the most consistent mechanism linking between solar variations and climate change. I will end...
Article
Some observations suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae as do several models. Establishing a causal connection between these mass-loss episodes and the final explosion would provide a novel way to study pre-supernova massive-star evolution. Here we report observations of a ma...
Article
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Some observations suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae, as do several models. Establishing a causal connection between these mass-loss episodes and the final explosion would provide a novel way to study pre-supernova massive-star evolution. Here we report observations of a m...
Article
The 20th century temperature anomaly record is reproduced using an energy balance model, with a diffusive deep ocean. The model takes into account all the standard radiative forcings, and in addition the possibility of a non-thermal solar component. The model is parameterized and then optimized to produce the most likely values for the climate para...
Article
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We study C/O white dwarfs with masses of 1.0 to 1.4 Msun accreting solar-composition material at very high accretion rates. We address the secular changes in the WDs, and in particular, the question whether accretion and the thermonuclear runaways result is net accretion or erosion. The present calculation is unique in that it follows a large numbe...
Article
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We study the dynamics of continuum driven winds from rotating stars, and develop an approximate analytical model. We then discuss the evolution of stellar angular momentum, and show that just above the Eddington limit, the winds are sufficiently concentrated towards the poles to spin up the star. A twin-lobe structure of the ejected nebula is seen...
Article
Supermassive stars (SMSs) are massive hydrogen objects that slowly radiate their gravitational binding energy. Such hypothetical primordial objects may have been the seed of the massive black holes (BHs) observed at the centre of galaxies. Under the standard picture, these objects can be approximately described as n = 3 polytropes, and they are exp...
Article
We generalize the problem of the semi-gray model to cases in which a non-negligible fraction of the stellar radiation falls on the long-wavelength range, and/or that the planetary long-wavelength emission penetrates into the transparent short wavelength domain of the absorption. Second, applying the most general assumptions and independently of any...
Article
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We review the physics of continuum-driven mass loss and the role it plays in η Carinae and other LBVs. Unlike line-driven mass loss, which is inherently lim-ited by self-shadowing, continuum driving can in principle lead to mass-loss rates up to the "photon-tiring" limit, for which the energy to lift the outflow becomes equal to the stellar luminos...
Article
The high luminosities and long decays of classical novae imply that they should be described as evolving super-Eddington (SED) steady states. We begin by describing how such states can exist--through the rise of a ``porous layer" which reduces the effective opacity, and then discuss other characteristics of these states, in particular, that a conti...
Article
We consider a scenario where supermassive black holes form through direct accumulation of gas at the centre of proto-galaxies. In the first stage, the accumulated gas forms a super-massive star whose core collapses when the nuclear fuel is exhausted, forming a black hole of MBH≈ 100 M⊙. As the black hole starts accreting, it inflates the surroundin...
Article
We construct Super-Eddington Slim discs models around both stellar and supermassive black holes by allowing the formation of a porous layer with a reduced effective opacity. Unlike the standard scenario in which the discs become thick, super-Eddington discs remain slim. In addition, they accelerate a significant wind with a ‘thick disc’ geometry. W...
Article
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Rahmstorf et al. (2004) published a "critique" of the article "Celectial driver of Phanerozoic Cli- mate?" (Shaviv & Veizer, 2003). Our rebuttal was published in Eos (and an unabridged version can be found at http://www.phys.huji.ac.il/~shaviv/ClimateDebate), together with with Rahm- storf et al.'s reply. Since Eos denied us the opportunity to resp...
Article
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We construct Super-Eddington Slim Disks models around both stellar and super-massive black holes by allowing the formation of a porous layer with a reduced effective opacity. We show that at high accretion rates, the inner part of the disks become radiation pressure dominated. However, unlike the standard scenario in which the disks become thick, s...
Article
We calculate the effect that CO_2 enhancement has on the radiative transfer in the Earth atmosphere. To this goal, we apply a recent algorithm developed by Wehrse and Shaviv. The calculation differs from previous calculations in that it includes several million molecular lines and in that it iterates for the temperature profile, so as to satisfy ra...
Article
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We briefly review the characteristics of super-Eddington (SED) states which arise in various astrophysical systems. These include classical nova eruptions, giant LBV eruptions, super-massive objects (SMOs) and very high accretion rate flows. The former two have ample observational data to establish the existence of SED states and learn of their beh...
Article
The minimum of solar cycle 23 has been the deepest minimum of the space age. This period has been characterized by an unprecedented number of sunspot-less days (i.e., days without any sunspots) and a very low magnitude of the solar dipole field strength -which have in turn resulted in very low solar irradiance and historically high values of cosmic...
Article
We show that inhomogeneity of cosmic ray (CR) sources, due to the concentration of supernova remnants (SNRs) towards the galactic spiral arms, can naturally explain the anomalous increase in the positron/electron ratio observed by PAMELA. We consistently recover the observed positron fraction between 1 and 100 GeV using SNRs as the sole source of C...
Article
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Recent measurements of the positron/electron ratio in the cosmic ray (CR) flux exhibits an apparent anomaly, whereby this ratio increases between 10 and 100 GeV. In contrast, this ratio should decrease according to the standard scenario, in which CR positrons are secondaries formed by hadronic interactions between the primary CR protons and the int...
Article
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Recent measurements of the positron/electron ratio in the cosmic ray (CR) flux exhibits an apparent anomaly, whereby this ratio increases between 10 and 100 GeV. We show that inhomogeneity of CR sources on a scale of order a kpc, can naturally explain this anomaly. If the nearest major CR source is about a kpc away, then low energy electrons ($\sim...
Article
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We apply the method of Shaviv & Shaviv to evaluate from first principles the plasma screening correction to the rate of nuclear reactions under conditions similar to those prevailing in the present-day Sun. We calculate the screening factor for the p-p chain and the CN cycle nuclear reactions. We find the following:
Article
We investigate the following two questions of principle: (1) Does the ion's kinetic energy affect its electrostatic potential energy when the ion is in statistical equilibrium with the plasma? In other words, is there a difference between a potential energy of a test particle moving in the plasma and the potential energy of a particle in statistica...
Article
Stars can produce steady-state winds through radiative driving as long as the mechanical luminosity of the wind does not exceed the radiative luminosity at its base. This upper bound on the mass-loss rate is known as the photon-tiring limit. Once above this limit, the radiation field is unable to lift all the material out of the gravitational poten...
Article
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1] Over the 11-year solar cycle, small changes in the total solar irradiance (TSI) give rise to small variations in the global energy budget. It was suggested, however, that different mechanisms could amplify solar activity variations to give large climatic effects, a possibility which is still a subject of debate. With this in mind, we use the oce...
Article
We present the results of numerical simulations of continuum-driven winds of stars that exceed the Eddington limit and compare these against predictions from earlier analytical solutions. Our models are based on the assumption that the stellar atmosphere consists of clumped matter, where the individual clumps have a much larger optical thickness th...
Article
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Continuum driving is an effective method to drive a strong stellar wind. It is governed by two limits: the Eddington limit and the photon-tiring limit. A star must exceed the effective Eddington limit for continuum driving to overcome the stellar gravity. The photon-tiring limit places an upper limit on the mass loss rate that can be driven to infi...
Article
The Milky Way spiral arm kinematics is studied using the birth place of open clusters. We separately study the nearby spiral arms, and find evidence for multiple spiral sets. In particular, the Sagittarius–Carina arm appears to be a superposition of two sets. The first has a pattern speed of , while the second has . The Perseus arm located at large...
Chapter
We present the effects that inhomogeneities have on radiating atmospheres. It is shown that nonuniformities in a medium induce a reduction of the effective opacity which subsequently increases the Eddington Luminosity. The most striking effect however that arises from the dependence of the opacity on the inhomogeneities, is the possibility of a pha...
Article
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In recent years the variability of the cosmic ray flux has become one of the main issues interpreting cosmogenic elements and especially their connection with climate. In this review, an interdisciplinary team of scientists brings together our knowledge of the evolution and modulation of the cosmic ray flux from its origin in the Milky Way, during...
Chapter
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We review the long-term variations in the galactic environment in the vicinity of the solar system. These include changes in the cosmic ray flux, in the pressure of the different interstellar components and possibly even gravitational tides. On very long time scales, the variations arise from the variable star formation rate of the MilkyWay, while...
Article
Shortly after the discovery of the binary system PSR J0737-3039 we predicted that it has a small proper motion and suggested that this implies that the progenitor mass of the younger pulsar (B) must be around 1.45M_sun. This is in contradiction to standard evolutionary scenarios that suggest a He-star progenitor with M >2.1-2.3M_sun and in sharp co...
Article
We review the expect role of the cosmic ray climate link on different time scales We show that while it is dominant over some scales it is only expected to be secondary over others We then continue with an estimate of the climate sensitivity to changes in the radiative budget based on empirical comparison between reconstructed changes in the global...
Article
We discuss the problem of cosmic ray diffusion in the Milky Way and show that the spiral arm dynamics gives rise to a ~ 150 Myr periodic modulation of the cosmic ray density in the vicinity of the solar system. We show that these predicted variations are recorded in the exposure ages of Iron meteorites. Given the suspected cosmic ray-climate link,...
Article
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We review the current theory describing the existence of steady state super-Eddington atmospheres. The key to the understanding of these atmospheres is the existence of a porous layer responsible for a reduced effective opacity. We show how porosity arises from radiative-hydrodynamic instabilities and why the ensuing inhomogeneities reduce the effe...
Article
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In the presence of strong magnetic fields, the vacuum becomes a birefringent medium. We show that this QED effect couples the direction of the polarization of photons leaving the NS surface, to the direction of the magnetic field along the ray's path. We analyze the consequences that this effect has on aligning the polarization vectors to generate...
Article
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Evolutionary scenarios suggest that the progenitor of the new binary pulsar J0737-3039B was a He star with M>(2.1-2.3)M. . We show that this case implies that the binary must have a large (>120 km/s) center of mass velocity. However, the location, approximately 50 pc from the Galactic plane, suggests that the system has, at high likelihood, a signi...
Chapter
We map and study the dynamics of the Milky Way’s spiral arms in our vicinity, using the birth place of open clusters. Since these objects are located in the galactic plane and are born primarily in the arms, they are an excellent tool for analyzing the dynamics of the spiral structure. Using their birth place, we find evidence for multiple spiral p...
Article
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Rahmstorf et al. [2004], in their “critique” of Shaviv and Veizer [2003], assert that the proposed correlation between cosmic ray flux (CRF) and paleoclimate during the Phanerozoic does not “hold up under scrutiny” because its astrophysical background is based on “questionable assumptions” and circular reasoning, and because the meteoritic and terr...
Article
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We examine the results linking cosmic ray flux (CRF) variations to global climate change. We then proceed to study various periods over which there are estimates for the radiative forcing, temperature change and CRF variations relative to today. These include the Phanerozoic as a whole, the Cretaceous, the Eocene, the Last Glacial Maximum, the 20th...
Article
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Royer et al. (2004) introduce a seawater pH correction to the Phanerozoic temperature recon- struction based on �18O variations in marine fossils. Although this correction is a novel idea and it is likely to have played some role in offsetting the �18O record, we show that (a) The correction cannot be as large as claimed by Royer et al. (b) Irrespe...
Article
The ionization state of ⁷Be in the solar core affects the prediction of the solar ⁸B neutrino flux. Recently, Shaviv & Shaviv (2003) examined the theory and the effect of pressure ionization on the ionization state of ⁷Be and all elements with 12 ⩾ Z ⩾ 4. It was shown that under the conditions prevailing in the solar core, the ionization state is d...
Article
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We examine radiatively driven mass loss from stars near and above the Eddington limit (Ledd). We begin by reviewing the instabilities that are expected to form extensive structure near Ledd. We investigate how this "porosity" can reduce the effective coupling between the matter and radiation. Introducing a new "porosity-length'' formalism, we deriv...
Article
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The observed orbital parameters of the recently discovered binary pulsar J0737-3039 are used to constrain the progenitor system. In particular, the small observed eccentricity and the small inferred peculiar velocity imply that during the formation of the second NS in the system, a very small mass Delta M <~ 0.15 Msun, was ejected. A progenitor mor...
Article
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Standard solar models predict a solar luminosity that gradually increased by about 30% over the past 4.5 billion years. Under the faint sun, Earth should have been frozen solid for most of its existence. Yet, running water is observed to have been present since very early in Earth's history. This enigma is known as the faint sun paradox. We show he...
Article
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