Detecting Changing Polarization Structures in Sagittarius A* with High Frequency VLBI (2009)
Fish, Vincent L., Doeleman, Sheperd S., Broderick, Avery E., Loeb, Abraham, Rogers, Alan E. E.
Sagittarius A* is the source of near infrared, X-ray, radio, and (sub)millimeter emission associated with the supermassive black hole at the Galactic Center. In the submillimeter regime, Sgr A*...
Mergers of gas-rich galaxies lead to black hole binaries that coalesce as a result of dynamical friction on the ambient gas. Once the binary tightens to
Moro-Martin, Amaya, Turner, Edwin L., Loeb, Abraham
Planetesimal formation is a common by-product of the star formation process. Taking the dynamical history of the Solar system as a guideline -- in which the planetesimal belts were heavily depleted...
Pritchard, Jonathan R., Loeb, Abraham, Wyithe, J. Stuart B.
In this paper, we explore the constraints on the reionization history that are provided by current observations of the Lyman-alpha forest and the CMB. Rather than using a particular semi-analytic...
Signatures of Relativistic Helical Motion in the Rotation Measures of AGN Jets (2009)
Broderick, Avery E, Loeb, Abraham
Polarization has proved an invaluable tool for probing magnetic fields in relativistic jets. Maps of the intrinsic polarization vectors have provided the best evidence to date for uniform, toroidally...
Barkana, Rennan, Loeb, Abraham
Gravitational lensing observations of massive X-ray clusters imply a steep characteristic density profile marked by a central concentration of dark matter. The observed mass fraction within a...
Probing the Epoch of Reionization with the Lyman Alpha Forest at z~4-5 (2009)
Cen, Renyue, McDonald, Patrick, Trac, Hy, Loeb, Abraham
The inhomogeneous cosmological reionization process leaves tangible imprints in the intergalactic medium down to z=4-5. The Lyman-alpha forest flux power spectrum provides a potentially powerful...
Galaxy Statistics in Pencil-beam Surveys at High Redshifts (2009)
Muñoz, Joseph A., Trac, Hy, Loeb, Abraham
Surveys of faint galaxies at high redshifts often result in a "pencil-beam" geometry that is much longer along the line-of-sight than across the sky. We explore the effects of this geometry on the...
Probing the Epoch of Reionization with Milky Way Satellites (2009)
Muñoz, Joseph A., Madau, Piero, Loeb, Abraham, Diemand, Jürg
While the connection between high-redshift star formation and the local universe has recently been used to understand the observed population of faint dwarf galaxies in the Milky Way (MW) halo, we...
The hyperfine transition of 3He+ as a probe of the intergalactic medium (2009)
We explore the prospects of using the hyperfine transition of 3He+ as a probe of the intergalactic medium. The emission signal from ionized regions during reionization is expected to be...
The Pulsar Contribution to the Gamma-Ray Background (2009)
We estimate the contribution of Galactic pulsars, both ordinary and millisecond pulsars (MSPs), to the high-energy (>100 MeV) gamma-ray background. We pay particular attention to the high-latitude...
The Kinetic Sunyaev-Zel'dovich effect of the Milky Way Halo (2009)
Birnboim, Yuval, Loeb, Abraham
We calculate the expected imprint of the ionized gas in the Milky-Way halo on the Cosmic Microwave Background (CMB) through the kinetic Sunyaev-Zel'dovich (kSZ) effect. Unlike other Galactic...
The Event Horizon of Sagittarius A* (2009)
Broderick, Avery E., Loeb, Abraham, Narayan, Ramesh
Black hole event horizons, causally separating the external universe from compact regions of spacetime, are one of the most exotic predictions of General Relativity (GR). Until recently, their...
Active Galactic Nuclei (AGN) produce a dominant fraction (~80%) of the Soft X-ray background (SXB) at photon energies 0.5
In Situ Probes of the First Galaxies and Reionization: Gamma-ray Bursts (2009)
McQuinn, Matthew, Bloom, Joshua S., Grindlay, Jonathan, Band, David, Barthelmy, S. D., Berger, E., ...
The first structures in the Universe formed at z>7, at higher redshift than all currently known galaxies. Since GRBs are brighter than other cosmological sources at high redshift and exhibit simple...
Strong gravitational lensing probes of the particle nature of dark matter (2009)
Moustakas, Leonidas A., Abazajian, Kevork, Benson, Andrew, Bolton, Adam S., Bullock, James S., Chen, Jacqueline, ...
There is a vast menagerie of plausible candidates for the constituents of dark matter, both within and beyond extensions of the Standard Model of particle physics. Each of these candidates may have...
Cosmology from the Highly-Redshifted 21 cm Line (2009)
Furlanetto, Steven, Lidz, Adam, Loeb, Abraham, McQuinn, Matthew, Pritchard, Jonathan, Shapiro, Paul, ...
One of the next decade's most exciting prospects is to explore the cosmic "dark ages," during which the first stars in the Universe formed, with the 21 cm line of neutral hydrogen. At z>6, this light...
Explaining the Observed Lyman Alpha `Blobs' as Cold Streams of Gas in the Halos of Galaxies (2009)
Over the past decade, mysterious blobs of Lyman alpha (Lya) emission by hydrogen have been discovered in the vicinity of galaxies at early cosmic times. Although a number of possible models were...
Astrophysics from the Highly-Redshifted 21 cm Line (2009)
Furlanetto, Steven, Lidz, Adam, Loeb, Abraham, McQuinn, Matthew, Pritchard, Jonathan, Aguirre, James, ...
The cosmic dark ages and the epoch of reionization, during which the first generations of stars and galaxies formed, are among the most compelling frontiers of extragalactic astrophysics and...
Bloom, Joshua S., Holz, Daniel E., Hughes, Scott A., Menou, Kristen, Adams, Allan, Anderson, Scott F., ...
It is widely expected that the coming decade will witness the first direct detection of gravitational waves (GWs). The ground-based LIGO and Virgo GW observatories are being upgraded to advanced...
Imprint of distortions in the Oort Cloud on the CMB anisotropies (2009)
We study the effect of a close encounter of a passing star on the shape of the inner Oort Cloud, using the impulse approximation. The deviation of the perturbed Oort Cloud from sphericity adds...
Imaging the Black Hole Silhouette of M87: Implications for Jet Formation and Black Hole Spin (2008)
Broderick, Avery E., Loeb, Abraham
The silhouette cast by the horizon of the supermassive black hole in M87 can now be resolved with the emerging millimeter very-long baseline interferometry (VLBI) capability. Despite being ~2000...
Cosmological Constraints from 21cm Surveys After Reionization (2008)
Visbal, Eli, Loeb, Abraham, Wyithe, Stuart
21cm emission from residual neutral hydrogen after the epoch of reionization can be used to trace the cosmological power spectrum of density fluctuations. Using a Fisher matrix formulation, we...
The Race Between Stars and Quasars in Reionizing Cosmic Hydrogen (2008)
The cosmological background of ionizing radiation has been dominated by quasars once the Universe aged by ~2 billion years. At earlier times (redshifts z>3), the observed abundance of bright quasars...
Evidence for Merger-Driven Activity in the Clustering of High Redshift Quasars (2008)
Recently, a very large clustering length has been measured for quasars at a redshift of z~4. In combination with the observed quasar luminosity function we assess the implications of this clustering...
Using Millimeter VLBI to Constrain RIAF Models of Sagittarius A* (2008)
Fish, Vincent L., Broderick, Avery E., Doeleman, Sheperd S., Loeb, Abraham
The recent detection of Sagittarius A* at lambda = 1.3 mm on a baseline from Hawaii to Arizona demonstrates that millimeter wavelength very long baseline interferometry (VLBI) can now spatially...
Estimating the Parameters of Sgr A*'s Accretion Flow Via Millimeter VLBI (2008)
Broderick, Avery E., Fish, Vincent L., Doeleman, Sheperd S., Loeb, Abraham
Recent millimeter-VLBI observations of Sagittarius A* (Sgr A*) have, for the first time, directly probed distances comparable to the horizon scale of a black hole. This provides unprecedented access...
Star Clusters Around Recoiled Black Holes in the Milky Way Halo (2008)
O'Leary, Ryan M., Loeb, Abraham
Gravitational wave emission by coalescing black holes (BHs) kicks the remnant BH with a typical velocity of hundreds of km/s. This velocity is sufficiently large to remove the remnant BH from a...
Constraints on the Local Sources of Ultra High-Energy Cosmic Rays (2008)
Ultra high-energy cosmic rays (UHECRs) are believed to be protons accelerated in magnetized plasma outflows of extra-Galactic sources. The acceleration of protons to ~10^{20} eV requires a source...
Methods for detecting flaring structures in Sagittarius A* with high frequency VLBI (2008)
Doeleman, Sheperd S., Fish, Vincent L., Broderick, Avery E., Loeb, Abraham, Rogers, Alan E. E.
The super massive black hole candidate, Sagittarius A*, exhibits variability from radio to X-ray wavelengths on time scales that correspond to < 10 Schwarzschild radii. We survey the potential of...
Acceleration of Galactic Supershells by Lyman Alpha Radiation (2008)
Scattering of Lyman Alpha (hereafter Lya) photons by neutral hydrogen gas in a single outflowing 'supershell' around star forming regions often explains the shape and offset of the observed Lya...
The 21cm Power Spectrum After Reionization (2008)
We discuss the 21cm power spectrum (PS) following the completion of reionization. In contrast to the reionization era, this PS is proportional to the PS of mass density fluctuations, with only a...
Shattow, Genevieve, Loeb, Abraham
We examine the implications of recent measurements of the Milky Way rotation for the trajectory of the Large Magellanic Cloud. The ~ 14+/-6% increase in the MW circular velocity relative to the IAU...
Trac, Hy, Cen, Renyue, Loeb, Abraham
We study the impact of inhomogeneous hydrogen reionization on the thermal evolution of the intergalactic medium (IGM) using hydrodynamic + radiative transfer simulations where reionization is...
Gravitational waves from scattering of stellar-mass black holes in galactic nuclei (2008)
O'Leary, Ryan M., Kocsis, Bence, Loeb, Abraham
Stellar mass black holes (BHs) are expected to segregate and form a steep density cusp around supermassive black holes (SMBHs) in galactic nuclei. We follow the evolution of a multi-mass system of...
Lyman Alpha Driven Outflows Around Star Forming Galaxies (2008)
We present accurate Monte-Carlo calculations of Lyman Alpha (hereafter Lya) radiation pressure in a range of models which represent galaxies during various epochs of our Universe. We show that the...
Detecting Flaring Structures in Sagittarius A* with (Sub)Millimeter VLBI (2008)
Fish, Vincent L., Doeleman, Sheperd S., Broderick, Avery E., Loeb, Abraham, Rogers, Alan E. E.
Multiwavelength monitoring observations of Sagittarius A* exhibit variability on timescales of minutes to hours, indicating emission regions localized near the event horizon....
Existing upper limits on variations in the photospheric radius of the Sun during the solar magnetic activity cycle are at a fractional amplitude of 2x10^{-4}. At that level, the transit duration of a...
Effects of gravitational-wave recoil on the dynamics and growth of supermassive black holes (2008)
Simulations of binary black hole mergers indicate that asymmetrical gravitational wave (GW) emission can cause black holes to recoil at speeds up to thousands of km/s. These GW recoil events can...
The Density Contrast of the Shapley Supercluster (2008)
Muñoz, Joseph A., Loeb, Abraham
We calculate the density contrast of the Shapley Supercluster (SSC) based on the enhanced abundance of X-ray clusters in it using the extended Press-Schechter formalism. We derive a total SSC mass of...
Let there be Light: the Emergence of Structure out of the Dark Ages in the Early Universe (2008)
The initial conditions of our Universe can be summarized on a single sheet of paper. Yet the Universe is full of complex structures today, such as stars, galaxies and groups of galaxies. In this...
Mergers of supermassive black hole binaries release peak power of up to ~10^57 erg/s in gravitational waves (GWs). As the GWs propagate through ambient gas, they induce shear and a small fraction of...
21cm Absorption by Compact Hydrogen Disks Around Black Holes in Radio-Loud Nuclei of Galaxies (2008)
The clumpy maser disks observed in some galactic nuclei mark the outskirts of the accretion disk that fuels the central black hole and provide a potential site of nuclear star formation....
Evolution of the 21 cm signal throughout cosmic history (2008)
Pritchard, Jonathan R., Loeb, Abraham
The potential use of the redshifted 21 cm line from neutral hydrogen for probing the epoch of reionization is motivating the construction of several low-frequency interferometers. There is also much...
Limits on the Position Wander of Sgr A* (2008)
Reid, Mark J., Broderick, Avery E., Loeb, Abraham, Honma, Mareki, Brunthaler, Andreas
We present measurements with the VLBA of the variability in the centroid position of Sgr A* relative to a background quasar at 7-mm wavelength. We find an average centroid wander of 71 +/- 45...
Measurements of the 21cm line emission by residual cosmic hydrogen after reionization can be used to trace the power spectrum of density perturbations through a significant fraction of the observable...
The classical radiometer equation is commonly used to calculate the detectability of the 21cm emission by diffuse cosmic hydrogen at high redshifts. However, the classical description is only valid...
Dynamical Constraints on the Local Group from the CMB and 2MRS Dipoles (2007)
Loeb, Abraham, Narayan, Ramesh
We place constraints on the dynamics of the Local Group (LG) by comparing the dipole of the Cosmic Microwave Background (CMB) with the peculiar velocity induced by the 2MRS galaxy sample. The...
Formation and Signatures of the First Stars and Quasars (2007)
Zoltan Haiman, An Haiman, Abraham Loeb
. We examine various observable signatures of the first generation of stars and low-- luminosity quasars, including the metal enrichment, radiation background, and dust opacity/emission that they...
Optical Appearance of the Debris of a Star Disrupted by a Massive Black Hole (2007)
Abraham Loeb, Andrew Ulmer, Erg S
We show that the disruption of a star by a ¸ 10 6 M fi black hole in a galactic nucleus could under favorable circumstances produce an optically--thick envelope that radiates with a thermal spectrum...
The Frontier of Reionization: Theory and Forthcoming Observations (2007)
The cosmic microwave background provides an image of the Universe 0.4 million years after the big bang, when atomic hydrogen formed out of free electrons and protons. One of the primary goals of...
The Polarization of Scattered Lyman Alpha Radiation Around High-Redshift Galaxies (2007)
The high-redshift Universe contains luminous Lyman Alpha (hereafter Lya) emitting sources such as galaxies and quasars. The emitted Lya radiation is often scattered by surrounding neutral hydrogen...
Light-Cone Distortion of the Clustering and Abundance of Massive Galaxies at High-Redshifts (2007)
Muñoz, Joseph A., Loeb, Abraham
Observational surveys of galaxies are not trivially related to single-epoch snapshots from computer simulations. Observationally, an increase in the distance along the line-of-sight corresponds to an...
Muñoz, Joseph A., Loeb, Abraham
Massive high-redshift galaxies form in over-dense regions where the probability of forming other galaxies is also strongly enhanced. Given an observed flux of a galaxy, the inferred mass of its host...
Baryonic Acoustic Oscillations in 21cm Emission: A Probe of Dark Energy out to High Redshifts (2007)
Wyithe, Stuart, Loeb, Abraham, Geil, Paul
Low-frequency observatories are currently being constructed with the goal of detecting redshifted 21cm emission from the epoch of reionization. These observatories will also be able to detect...
Hypervelocity Stars from the Andromeda Galaxy (2007)
Sherwin, Blake D., Loeb, Abraham, O'Leary, Ryan M.
Hypervelocity stars (HVSs) discovered in the Milky Way (MW) halo are thought to be ejected from near the massive black hole (MBH) at the galactic centre. In this paper we investigate the spatial and...
Fluctuations in 21cm Emission After Reionization (2007)
The fluctuations in the emission of redshifted 21cm photons from neutral inter-galactic hydrogen will provide an unprecedented probe of the reionization era. Conventional wisdom assumes that this...
Current observations are about to open up a direct window into the final frontier of cosmology: the first billion years in cosmic history when the first stars and galaxies formed. Even before the...
Barkana, Rennan, Loeb, Abraham
A new generation of radio telescopes are currently being built with the goal of tracing the cosmic distribution of atomic hydrogen at redshifts 6-15 through its 21-cm line. The observations will...
The Collision Between The Milky Way And Andromeda (2007)
We use a N--body/hydrodynamic simulation to forecast the future encounter between the Milky Way and the Andromeda galaxies, given current observational constraints on their relative distance,...
Imprint of Distortions in the Oort Cloud on the CMB Anisotropies (2007)
We study the effect of a close encounter of a passing star on the shape of the inner Oort Cloud, using the impulse approximation. The deviation of the perturbed Oort Cloud from sphericity adds...
Distortion of Gravitational-Wave Packets Due to their Self-Gravity (2007)
When a source emits a gravity-wave (GW) pulse over a short period of time, the leading edge of the GW signal is redshifted more than the inner boundary of the pulse. The GW pulse is distorted by the...
According to recent general-relativistic simulations, the coalescence of two spinning black holes (BHs) could lead to recoil speeds of the BH remnant of up to thousands of km/s as a result of the...
Missing Pages in Our Photo Album of the Infant Universe (2007)
Existing data sets include an image of the Universe when it was 0.4 million years old (in the form of the cosmic microwave background), as well as images of individual galaxies when the Universe was...
Properties of the Radio-Emitting Gas Around SgrA* (2007)
We show that the radial profiles of the temperature and density of the electrons as well as the magnetic field strength around the massive black hole at the Galactic center, SgrA*, may be constrained...
Cosmic microwave background anisotropies from outflows in Lyman break galaxies (2007)
Babich, Daniel, Loeb , Abraham
Thomson scattering of the cosmic microwave background (CMB) on moving electrons in the outflows of Lyman break galaxies (LBGs) at redshifts 2–8 contributes to the small-scale CMB anisotropies. The...
Dynamics of triple black hole systems in hierarchically merging massive galaxies (2006)
Galaxies with stellar bulges are generically observed to host supermassive black holes (SMBHs). The hierarchical merging of galaxies should therefore lead to the formation of SMBH binaries. Merging...
The Physics and Early History of the Intergalactic Medium (2006)
Barkana, Rennan, Loeb, Abraham
The intergalactic medium - the cosmic gas that fills the great spaces between the galaxies - is affected by processes ranging from quantum fluctuations in the very early universe to radiative...
Loeb, Abraham, Zaldarriaga, Matias
The question of whether intelligent life exists elsewhere is one of the fundamental unknowns about our Universe. Over the past decade more than 200 extra-solar planets have been discovered, providing...
Hypervelocity Collisions of Binary Stars at the Galactic Centre (2006)
Recent surveys have identified seven hypervelocity stars (HVSs) in the halo of the Milky Way. Most of these stars may have originated from the breakup of binary star systems by the nuclear black hole...
CMB Anisotropies from Outflows in Lyman Break Galaxies (2006)
Thomson scattering of the Cosmic Microwave Background (CMB) on moving electrons in the outflows of Lyman Break Galaxies (LBGs) at redshifts 2-8 contributes to the small-scale CMB anisotropies. The...
O'Leary, Ryan M., Loeb, Abraham
Stars within 0.1 pc of the supermassive black hole Sgr A* at the Galactic centre are expected to encounter a cluster of stellar-mass black holes (BHs) that have segregated to that region. Some of...
Assessing The Starburst Contribution to the Gamma-Ray and Neutrino Backgrounds (2006)
Thompson, Todd A., Quataert, Eliot, Waxman, Eli, Loeb, Abraham
If cosmic ray protons interact with gas at roughly the mean density of the interstellar medium in starburst galaxies, then pion decay in starbursts is likely to contribute significantly to the...
Requirements for Cosmological 21-cm Masers (2006)
We perform Monte-Carlo calculations of the radiative transfer of Lyman Alpha (hereafter Lya) photons emitted by a source embedded in a neutral collapsing gas cloud. This represents a young galaxy or...
Testing General Relativity with High-Resolution Imaging of Sgr A* (2006)
Broderick, Avery, Loeb, Abraham
Submilliarcsecond astrometry and imaging of the black hole Sgr A* at the Galactic Center may become possible in the near future at infrared and submillimetre wavelengths. This resolution is...
Smooth Boundaries to Cosmological HII Regions from Galaxy Clustering (2006)
The HII regions around quasars and galaxies at redshifts beyond the epoch of reionisation will provide prime targets for upcoming 21cm campaigns using a new generation of low-frequency radio...
Thermal Evaporation of Gas from X-ray Clusters (2006)
A fraction of the thermal protons in the outer envelope of an X-ray cluster have velocities that exceed the local escape speed from the cluster gravitational potential. The Coulomb mean-free-path of...
An Observational Test for the Anthropic Origin of the Cosmological Constant (2006)
The existence of multiple regions of space beyond the observable Universe (within the so-called "multiverse") where the vacuum energy density takes different values, has been postulated as an...
Dwarf Galaxy Formation Was Suppressed By Cosmic Reionization (2006)
A large number of faint galaxies, born less than a billion years after the big bang, have recently been discovered. The fluctuations in the distribution of these galaxies contributed to a scatter in...
The first dwarf galaxies, which constitute the building blocks of the collapsed objects we find today in the Universe, had formed hundreds of millions of years after the big bang. This pedagogical...
The Cumulative Bakground of High-Energy Neutrinos from Starburst Galaxies (2006)
We show that starburst galaxies convert efficiently cosmic-rays into pions, which in turn decay into high-energy neutrinos and photons. The cumulative background of GeV neutrinos is...
GRB Cosmology and the First Stars (2006)
Gamma-Ray Bursts (GRBs) are unique probes of the cosmic star formation history and the state of the intergalactic medium up to the redshifts of the first stars. In particular, the ongoing {\it Swift}...
Light-cone anisotropy in 21cm fluctuations during the epoch of reionization (2005)
Barkana, Rennan, Loeb, Abraham
The delay in light travel time along the line of sight generates an anisotropy in the power spectrum of 21cm brightness fluctuations from the epoch of reionization. We show that when the fluctuations...
Three-Body Kick to a Bright Quasar out of Its Galaxy During a Merger (2005)
The quasar HE0450-2958 was recently discovered to reside ~7kpc away from a galaxy that was likely disturbed by a recent merger. The lack of a massive spheroid of stars around the quasar raised the...
The Fate of Former Companions to Hypervelocity Stars Originating at the Galactic Center (2005)
The hypervelocity star SDSS J090745.0+024507 in the halo of the Milky Way galaxy (Brown et al. 2005) most likely originated from the breakup of a binary star system by the central black hole, SgrA*...
Detecting Reionization in the Star Formation Histories of High-Redshift Galaxies (2005)
Barkana, Rennan, Loeb, Abraham
The reionization of cosmic hydrogen, left over from the big bang, increased its temperature to >~ 1.e4 K. This photo-heating resulted in an increase of the minimum mass of galaxies and hence a...
We consider the effects of inhomogeneous reionization on the distribution of galaxies at high redshifts. Modulation of the formation process of the ionizing sources by large scale density modes makes...
High-Redshift Gamma-Ray Bursts from Population III Progenitors (2005)
Detection of gamma-ray bursts (GRBs) from redshifts z > 7 would open a new window into the earliest epoch of cosmic star formation. We construct separate star formation histories at high redshifts...
Nonthermal THz to TeV Emission from Stellar Wind Shocks in the Galactic Center (2005)
Quataert, Eliot, Loeb, Abraham
The central parsec of the Galaxy contains dozens of massive stars with a cumulative mass loss rate of ~ 10^{-3} solar masses per year. Shocks among these stellar winds produce the hot plasma that...
Broderick, Avery E., Loeb, Abraham
Sub milli-arcsecond astrometry and imaging of the black hole Sgr A* at the Galactic centre may become possible in the near future at infrared and sub-millimetre wavelengths. Motivated by observations...
Cosmic Variance In the Transparency of the Intergalactic Medium After Reionization (2005)
Following the completion of cosmic reionization, the mean-free-path of ionizing photons was set by a population of Ly-limit absorbers. As the mean-free-path steadily grew, the intensity of the...
Broderick, Avery E., Loeb, Abraham
The inferred black hole in the Galactic center spans the largest angle on the sky among all known black holes. Forthcoming observational programs plan to localize or potentially resolve the image of...
Loeb, Abraham, Reid, Mark J., Brunthaler, Andreas, Falcke, Heino
A major uncertainty in the dynamical history of the local group of galaxies originates from the unknown transverse speed of the Andromeda galaxy (M31) relative to the Milky Way. We show that the...
Imaging Bright Spots in the Accretion Flow Near the Black Hole Horizon of Sgr A* (2005)
Broderick, Avery E., Loeb, Abraham
Images from the vicinity of the black hole horizon at the Galactic centre (Sgr A*) could be obtained in the near future with a Very Large Baseline Array of sub-millimetre telescopes. The recently...
The Remnants of Intergalactic Supernovae (2005)
Maoz, Dan, Waxman, Eli, Loeb, Abraham
Intergalactic type-Ia supernovae (SNe-Ia) have been discovered recently in rich galaxy clusters, likely the descendants of an intergalactic stellar population found in recent years through a variety...
Prospects for Redshifted 21-cm observations of quasar HII regions (2005)
Wyithe, Stuart, Loeb, Abraham, Barnes, David
The introduction of low-frequency radio arrays over the coming decade is expected to revolutionize the study of the reionization epoch. Observation of the contrast in redshifted 21cm emission between...
Polarization of 21cm Radiation from the Epoch of Reionization (2005)
We consider the polarization of 21cm line radiation from the epoch of reionization due to both intrinsically polarized emission and secondary mechanisms. We argue that Thomson scattering of the 21cm...
Signature of Galactic Outflows as Absorption-Free Gaps in the Ly-alpha Forest (2005)
Fang, Taotao, Loeb, Abraham, Tytler, David, Kirkman, David, Suzuki, Nao
Powerful outflows from star-forming galaxies are expected to push away the neutral intergalactic medium (IGM) around those galaxies, and produce absorption-free gaps in the Ly-alpha forest. We...
The Small-Scale Power Spectrum of Cold Dark Matter (2005)
Loeb, Abraham, Zaldarriaga, Matias
One of the best motivated hypotheses in cosmology states that most of the matter in the universe is in the form of weakly-interacting massive particles that decoupled early in the history of the...
CMB B-mode polarization from Thomson scattering in the local universe (2005)
Hirata, Christopher M., Loeb, Abraham, Afshordi, Niayesh
The polarization of the cosmic microwave background (CMB) is widely recognized as a potential source of information about primordial gravitational waves. The gravitational wave contribution can be...
Probing the Epoch of Early Baryonic Infall Through 21cm Fluctuations (2005)
Barkana, Rennan, Loeb, Abraham
After cosmological recombination, the primordial hydrogen gas decoupled from the cosmic microwave background (CMB) and fell into the gravitational potential wells of the dark matter. The neutral...
A Dynamical Method for Measuring Masses of Stars with Transiting Planets (2005)
As a planet transits the face of a star, it accelerates along the line-of-sight. The changing delay in the propagation of photons produces an apparent deceleration of the planet across the sky...
CMB B-mode polarization from Thomson scattering in the local universe (2005)
Hirata, Christopher M., Loeb, Abraham, Afshordi, Niayesh
[Abridged] The polarization of the CMB is widely recognized as a potential source of information about primordial gravitational waves. The gravitational wave contribution can be separated from the...
Prospects for redshifted 21 cm observations of quasar H II regions (2005)
Wyithe, J. Stuart B., Loeb, Abraham, Barnes, David G.
The introduction of low-frequency radio arrays over the coming decade is expected to revolutionize the study of the reionization epoch. Observation of the contrast in redshifted 21 cm emission...
Prospects for redshifted 21 cm observations of quasar H II regions (2005)
Wyithe, J. Stuart B., Loeb, Abraham, Barnes, David G.
The introduction of low-frequency radio arrays over the coming decade is expected to revolutionize the study of the reionization epoch. Observation of the contrast in redshifted 21 cm emission...
Wyithe, Stuart, Loeb, Abraham, Carilli, Chris
We analyze the evolution of HII regions around the seven known SDSS quasars at z>6. The comparison between observed and model radii of the HII regions generated by these quasars individually,...
Detecting the Earliest Galaxies Through Two New Sources of 21cm Fluctuations (2004)
Barkana, Rennan, Loeb, Abraham
The first galaxies that formed at a redshift ~20-30 emitted continuum photons with energies between the Lyman-alpha and Lyman limit wavelengths of hydrogen, to which the neutral universe was...
Is Double Reionization Physically Plausible? (2004)
Furlanetto, Steven, Loeb, Abraham
Recent observations of z~6 quasars and the cosmic microwave background imply a complex history to cosmic reionization. Such a history requires some form of feedback to extend reionization over a long...
A Method for Separating the Physics from the Astrophysics of High-Redshift 21cm Fluctuations (2004)
Barkana, Rennan, Loeb, Abraham
Fluctuations in the 21cm brightness from cosmic hydrogen at redshifts z > 6 were sourced by the primordial density perturbations from inflation as well as by the radiation from galaxies. We propose a...
A Size of ~10 Mpc for the Ionized Bubbles at the End of Cosmic Reionization (2004)
The first galaxies to appear in the universe at redshifts z>20 created ionized bubbles in the intergalactic medium of neutral hydrogen left over from the Big-Bang. It is thought that the ionized...
The Environmental Impact of Supermassive Black Holes (2004)
The supermassive black holes observed at the centers of almost all present-day galaxies, had a profound impact on their environment. I highlight the principle of self-regulation, by which...
Searching for Intergalactic Shocks with the SKA (2004)
Keshet, Uri, Waxman, Eli, Loeb, Abraham
Strong intergalactic shocks are a natural consequence of structure formation in the universe. These shocks are expected to deposit large fractions of their energy in relativistic electrons (xi_e~0.05...
The discovery of Lyman-alpha emission from galaxies at redshifts beyond z~6.5 should not be naively interpreted as implying that the intergalactic medium (IGM) had been reionized at higher redsifts....
Implications of the Measured Image Size for the Radio Afterglow of GRB 030329 (2004)
Granot, Jonathan, Ramirez-Ruiz, Enrico, Loeb, Abraham
We use data on the image size of the radio afterglow of GRB 030329 (Taylor et al. 2004) to constrain the physical parameters of this explosion. Together with the observed broad band spectrum, this...
A model for the flaring radio emission in the double pulsar system J0737-3039 (2004)
The binary J0737-3039 A & B includes two pulsars in a highly relativistic orbit. The pulsed radio flux from pulsar B brightens considerably during two portions of each orbit. This phenomenon cannot...
Calibrating the Galaxy Halo - Black Hole Relation Based on the Clustering of Quasars (2004)
The observed number counts of quasars may be explained either by long-lived activity within rare massive hosts, or by short-lived activity within smaller, more common hosts. It has been argued that...
Was the Universe Reionized at Redshift 10? (2004)
Loeb, Abraham, Barkana, Rennan, Hernquist, Lars
Recently, Pello et al. (2004) claimed to have discovered a galaxy at a redshift z=10, and identified a feature in its spectrum with a hydrogen Lyman-alpha emission line. If this identification is...
A Limit from the X-ray Background on the Contribution of Quasars to Reionization (2004)
Dijkstra, Mark, Haiman, Zoltan, Loeb, Abraham
A population of black holes (BHs) at high redshifts (z>6) that contributes significantly to the ionization of the intergalactic medium (IGM) would be accompanied by the copious production of hard...
Sagiv, Amir, Waxman, Eli, Loeb, Abraham
(Abr) The origin and structure of magnetic fields in Gamma-Ray Burst (GRB) fireball plasmas are two of the most important open questions in all GRB models. We show that the structure and strength of...
Redshifted 21cm Signatures Around the Highest Redshift Quasars (2004)
The Ly-alpha absorption spectrum of the highest redshift quasars indicates that they are surrounded by giant HII regions, a few Mpc in size. The neutral gas around these HII regions should emit 21cm...
Milosavljevic, Milos, Loeb, Abraham
The discovery of hundreds of young, bright stars within a parsec from the massive black hole at the center of the Galaxy presents a challenge to star formation theories. The requisite Roche densities...
Cosmic Hydrogen Was Significantly Neutral a Billion Years After the Big Bang (2004)
The ionization fraction of cosmic hydrogen, left over from the big bang, provides crucial fossil evidence for when the first stars and quasar black holes formed in the infant universe. Spectra of the...
Early Formation and Late Merging of the Giant Galaxies (2004)
Gao, Liang, Loeb, Abraham, Peebles, P. J. E., White, Simon D. M., Jenkins, Adrian
Element segregation in giant galaxies and X-ray clusters (2003)
Chuzhoy, Leonid, Loeb, Abraham
We examine the process of element segregation by gravity in giant elliptical galaxies and X-ray clusters. We solve the full set of flow equations developed by Burgers for a multi-component fluid,...
Early Formation and Late Merging of the Giant Galaxies (2003)
Gao, Liang, Loeb, Abraham, Peebles, P. J. E., White, Simon D. M., Jenkins, Adrian
The most luminous galaxies in the present Universe are found at the centers of the most massive dark matter haloes, rich galaxy clusters. In the LCDM cosmology, such massive halo cores are present at...
Accretion onto a Primordial Protostar (2003)
We present a three-dimensional numerical simulation that resolves the formation process of a Population III star down to a scale of ~100 AU. The simulation is initialized on the scale of a dark...
Large-Scale Structure Shocks at Low and High Redshifts (2003)
Furlanetto, Steven, Loeb, Abraham
Cosmological simulations show that, at the present time, a substantial fraction of the gas in the intergalactic medium (IGM) has been shock-heated to T>10^5 K. Here we develop an analytic model to...
Loeb, Abraham, Zaldarriaga, Matias
The thermal evolution of the cosmic gas decoupled from that of the cosmic microwave background (CMB) at a redshift z~200. Afterwards and before the first stars had formed, the cosmic neutral hydrogen...
The comoving mass density of massive black hole (MBH) remnants from pre-galactic star formation could have been similar in magnitude to the mass-density of supermassive black holes (SMBHs) in the...
We show that the recently-discovered orbits of massive stars with closest approach of ~10^3 Schwarzschild radii from SgrA*, allow winds from these stars to provide the required mass deposition rate...
The Formation of the First Low-Mass Stars From Gas With Low Carbon and Oxygen Abundances (2003)
The first stars in the Universe are predicted to have been much more massive than the Sun. Gravitational condensation accompanied by cooling of the primordial gas due to molecular hydrogen, yields a...
Nagamine, Kentaro, Loeb, Abraham
We simulate the evolution of the intergalactic medium (IGM) in a universe dominated by a cosmological constant. We find that within a few Hubble times from the present epoch, the baryons will have...
Unusually Large Fluctuations in the Statistics of Galaxy Formation at High Redshift (2003)
Barkana, Rennan, Loeb, Abraham
We show that various milestones of high-redshift galaxy formation, such as the formation of the first stars or the complete reionization of the intergalactic medium, occurred at different times in...
We show that the time-dependent Doppler effect should induce measureable deviations of the time history of the projected orbit of a star around the supermassive black hole in the Galactic center...
The CMB Quadrupole in a Polarized Light (2003)
Doré, Olivier, Holder, Gilbert P., Loeb, Abraham
The low quadrupole of the cosmic microwave background (CMB), measured by COBE and confirmed by WMAP, has generated much discussion recently. We point out that the well-known correlation between...
Observing the First Stars, One Star at a Time (2003)
Gamma-Ray Bursts (GRBs) are believed to originate in compact remnants (black holes or neutron stars) of massive stars. Their high luminosities make them detectable out to the edge of the visible...
The Case for a Low Extragalactic Gamma-ray Background (2003)
Keshet, Uri, Waxman, Eli, Loeb, Abraham
Measurements of the diffuse extragalactic gamma-ray background (EGRB) are complicated by a strong Galactic foreground. Estimates of the EGRB flux and spectrum, obtained by modeling the Galactic...
Barkana, Rennan, Loeb, Abraham
Lyman-alpha absorption is a prominent cosmological tool for probing both galactic halos and the intergalactic medium at high redshift. We consider a variety of sources that can be used as the...
Radio Imaging of GRB Jets in Nearby Supernovae (2003)
Granot, Jonathan, Loeb, Abraham
We calculate the time evolution of the flux, apparent size, and image centroid motion of gamma-ray burst (GRB) radio jets, and show that they can be resolved by the VLBA at distances of hundreds of...
A Method for Mapping the Temperature Profile of X-ray Clusters Through Radio Observations (2003)
Holder, Gilbert, Loeb, Abraham
Many of the most luminous extragalactic radio sources are located at the centers of X-ray clusters, and so their radiation must be scattered by the surrounding hot gas. We show that radio...
Gravitationally redshifted absorption lines of Fe XXVI, Fe XXV, and O VIII were inferred recently in the X-ray spectrum of the bursting neutron star EXO 0748-676. We place an upper limit on the...
We postulate that supermassive black-holes grow in the centers of galaxies until they unbind the galactic gas that feeds them. We show that the corresponding self-regulation condition yields a...
Santos, Michael R., Loeb, Abraham
We present an observational test of the spectrum of the ionizing background at z~5; the test is sufficiently sensitive to determine whether Pop II or Pop III stars are the dominant source of ionizing...
Loeb, Abraham, Gaudi, B. Scott
Upcoming space-based photometric satellites offer the possibility of detecting continuum flux variability at the micro-magnitude level. We show that the Doppler flux variability induced by the reflex...
Effects of Wandering on the Coalescence of Black Hole Binaries in Galactic Centers (2003)
Chatterjee, Pinaki, Hernquist, Lars, Loeb, Abraham
We examine whether massive binary black holes in spherically symmetric bulges of galaxies can achieve coalescence through the emission of gravitational radiation under the action of stellar dynamical...
Was the Universe Reionized by Massive Population-III Stars? (2003)
The WMAP satellite has measured a large optical depth to electron scattering after cosmological recombination of 0.17+-0.04, implying significant reionization of the primordial gas only ~200 million...
The First Sources of Light (2003)
We review recent theoretical results on the formation of the first stars and quasars in the universe, and emphasize related open questions. In particular, we list important differences between the...
Gamma Rays from Intergalactic Shocks (2003)
Keshet, Uri, Waxman, Eli, Loeb, Abraham, Springel, Volker, Hernquist, Lars
Wang, Xiaohu, Loeb, Abraham, Waxman, Eli
We examine the stability of self-similar solutions for an accelerating relativistic blast wave which is generated by a point explosion in an external medium with a steep radial density profile of a...
Formation of the First Supermassive Black Holes (2002)
We consider the physical conditions under which supermassive black holes could have formed inside the first galaxies. Our SPH simulations indicate that metal-free galaxies with a virial temperature...
Metal Absorption Lines as Probes of the Intergalactic Medium Prior to the Reionization Epoch (2002)
Furlanetto, Steven, Loeb, Abraham
Winds from star-forming galaxies provide the most promising explanation for the enrichment of the intergalactic medium with heavy elements. Theoretical and observational arguments indicate that the...
Cosmological Origin of the Stellar Velocity Dispersions in Massive Early-Type Galaxies (2002)
Loeb, Abraham, Peebles, P. J. E.
We show that the observed upper bound on the line-of-sight velocity dispersion of the stars in an early-type galaxy, sigma6. Subsequently, the stars behaved dynamically just as an additional...
Spectral Signature of Cosmological Infall of Gas Around the First Quasars (2002)
Barkana, Rennan, Loeb, Abraham
Recent observations have shown that, only a billion years after the Big Bang, the Universe was already lit up by bright quasars fuelled by the infall of gas onto supermassive black holes. The masses...
Reionization of Hydrogen and Helium by Early Stars and Quasars (2002)
We compute the reionization histories of hydrogen and helium due to the ionizing radiation fields produced by stars and quasars. For the quasars we use a model based on halo-merger rates that...
Natarajan, Priyamvada, Loeb, Abraham, Kneib, Jean-Paul, Smail, Ian
The detailed distribution of mass within clusters of galaxies can be used to probe the nature of dark matter. We show that constraints on the extent of the mass distribution around galaxies in the...
The 21 cm Forest: Radio Absorption Spectra as Probes of Minihalos Before Reionization (2002)
Furlanetto, Steven, Loeb, Abraham
We study the absorption along lines of sight toward high-z radio sources caused by the 21 cm transition of neutral hydrogen in the intergalactic medium (IGM) before reionization. Using semi-analytic...
A Physical Model for the Luminosity Function of High-Redshift Quasars (2002)
We provide a simple theoretical model for the quasar luminosity function at high redshifts that naturally reproduces the statistical properties of the luminous SDSS quasar sample at redshifts z~4.3...
Galactic Constraints on the Sources of Ultra-High Energy Cosmic Rays (2002)
We show that if the sources of ultra-high energy cosmic rays (UHECRs) with energies E>10^{19}eV are associated with galaxies, then the production of UHECRs must occur in transient events. Our galaxy...
Intensive monitoring campaigns have recently attempted to measure the time delays between multiple images of gravitational lenses. Some of the resulting light-curves show puzzling low-level, rapid...
Nagamine, Kentaro, Loeb, Abraham
We simulate the future evolution of the observed inhomogeneities in the local universe assuming that the global expansion rate is dominated by a cosmological constant. We find that within two Hubble...
Effective Screening due to Minihalos During the Epoch of Reionization (2002)
Barkana, Rennan, Loeb, Abraham
We show that the gaseous halos of collapsed objects introduce a substantial cumulative opacity to ionizing radiation, even after the smoothly distributed hydrogen in the intergalactic medium has been...
Are X-ray Clusters Cooled by Heat Conduction to the Surrounding Intergalactic Medium? (2002)
We show that X-ray clusters would have cooled substantially over a Hubble time by transport of heat from their hot interior to the their envelope, if the heat conductivity had not been heavily...
Gravitational Lensing of the SDSS High-Redshift Quasars (2002)
We predict the effects of gravitational lensing on the color-selected flux-limited samples of z~4.3 and z>5.8 quasars, recently published by the Sloan Digital Sky Survey (SDSS). Our main findings...
Gravitational lenses magnify up to one third of the most distant quasars (2002)
Exceptionally bright quasars with redshifts up to z=6.28 have recently been discovered. Quasars are thought to be powered by the accretion of gas onto supermassive black holes at the centres of...
Identifying Gamma-Ray Burst Remnants Through Positron Annihilation Radiation (2002)
Furlanetto, Steven, Loeb, Abraham
We model the annihilation of relic positrons produced in a gamma-ray burst (GRB) after its afterglow has faded. We find that the annihilation signal from at least one GRB remnant in the Milky Way...
Gamma-Rays from Intergalactic Shocks (2002)
Keshet, Uri, Waxman, Eli, Loeb, Abraham, Springel, Volker, Hernquist, Lars
Structure formation in the intergalactic medium (IGM) produces large-scale, collisionless shock waves, where electrons can accelerate to highly relativistic energies. Such electrons can Compton...
Brownian Motion in Gravitationally-Interacting Systems (2002)
Chatterjee, Pinaki, Hernquist, Lars, Loeb, Abraham
We derive a model that describes the motion of a Brownian particle in a system which is dominated by gravitational forces. An example of such a system is a massive black hole immersed in a cluster of...
The Expected Redshift Distribution of Gamma-Ray Bursts (2002)
We predict the redshift distribution of Gamma-Ray Bursts (GRBs) assuming that they trace the cosmic star formation history. We find that a fraction >~50% of all GRBs on the sky originate at a...
Emission of Positron Annihilation Line Radiation by Clusters of Galaxies (2002)
Furlanetto, Steven, Loeb, Abraham
Clusters of galaxies are enriched with positrons from jets of active galactic nuclei (AGNs) or from the interaction of cosmic rays with the intracluster gas. We follow the cooling of these positrons...
Vacuum Decay Constraints on a Cosmological Scalar Field (2001)
Heyl, Jeremy S., Loeb, Abraham
If the potential of a scalar field, Phi, which currently provides the ``dark energy'' of the universe, has a negative minimum -M_0^4, then quantum-mechanical fluctuations could nucleate a bubble of...
An Intergalactic Magnetic Field from Quasar Outflows (2001)
Furlanetto, Steven, Loeb, Abraham
Outflows from quasars inevitably pollute the intergalactic medium (IGM) with magnetic fields. The short-lived activity of a quasar leaves behind an expanding magnetized bubble in the IGM. We model...
Element Diffusion During Cosmological Structure Formation (2001)
We consider element diffusion during the linear growth of structure in the intergalactic medium (IGM) before the redshift of reionization. The elements produced during big bang nucleosynthesis (such...
Wang, Xiaohu, Loeb, Abraham, Waxman, Eli
We analyze the stability of a relativistic double (forward/reverse) shock system which forms when the fireball of a Gamma-Ray Burst (GRB) impacts on the surrounding medium. We find this shock system...
Novel Ways to Probe the Universe with Gamma-Ray Bursts and Quasars (2001)
I consider novel ways by which Gamma-Ray Bursts (GRBs) and quasars can be used to probe the universe. Clues about how and when was the intergalactic medium ionized can be read off the UV emission...
Furlanetto, Steven, Loeb, Abraham
We propose to use gravitational wakes as a direct observational probe of the collisional nature of the dark matter. We calculate analytically the structure of a wake generated by the motion of a...
The Long-Term Future of Extragalactic Astronomy (2001)
If the current energy density of the universe is indeed dominated by a cosmological constant, then high-redshift sources will remain visible to us only until they reach some finite age in their...
Dynamics of a Massive Black Hole at the Center of a Dense Stellar System (2001)
Chatterjee, Pinaki, Hernquist, Lars, Loeb, Abraham
We develop a simple physical model to describe the dynamics of a massive point-like object, such as a black hole, near the center of a dense stellar system. It is shown that the total force on this...
Cosmological Studies with Gamma-Ray Bursts (2001)
Gamma-Ray Burst (GRB) explosions from the first generation of stars offer an exciting opportunity to probe the epoch of reionization. Clues about how and when the intergalactic medium was ionized can...
Constraining Cosmological Parameters Based on Relative Galaxy Ages (2001)
We propose to use relative galaxy ages as a means of constraining cosmological parameters. By measuring the age difference between two ensembles of old galaxies at somewhat different redshifts, one...
The Imprint of Lithium Recombination on the Microwave Background Anisotropies (2001)
Zaldarriaga, Matias, Loeb, Abraham
Following Loeb (2001), we explore the imprint of the resonant 6708A line opacity of neutral lithium on the temperature and polarization anisotropies of the cosmic microwave background (CMB) at...
Microlensing and the Surface Brightness Profile of the Afterglow Image of GRB 000301C (2001)
Gaudi, B. Scott, Granot, Jonathan, Loeb, Abraham
The optical afterglow of Gamma-Ray Burst (GRB) 000301C exhibited a significant, short-timescale deviation from the power-law flux decline expected in the standard synchrotron shock model. Garnavich,...
I show that neutral lithium couples strongly to the cosmic microwave background (CMB) through its 6708A resonant transition after it recombines at z~500. At observed wavelengths of 100). Observations...
TeV Neutrinos and GeV Photons from Shock Breakout in Supernovae (2001)
We show that as a Type II supernova shock breaks out of its progenitor star, it becomes collisionless and may accelerate protons to energies >10 TeV. Inelastic nuclear collisions of these protons...
Intergalactic Magnetic Fields from Quasar Outflows (2001)
Furlanetto, Steven, Loeb, Abraham
Outflows from quasars inevitably pollute the intergalactic medium (IGM) with magnetic fields. The short-lived activity of a quasar leaves behind an expanding magnetized bubble in the IGM. We model...
Resolving the Image of Gamma-Ray Burst Afterglows with Gravitational Microlensing (2001)
Gaudi, B. Scott, Loeb, Abraham
Microlensing of a gamma-ray burst afterglow by an intervening star can be used to infer the radial structure of the afterglow image. Near the peak of the microlensing event, the outer edge of the...
Chromatic Signatures in the Microlensing of GRB Afterglows (2001)
Granot, Jonathan, Loeb, Abraham
We calculate the radial surface brightness profile of the image of a Gamma-Ray-Burst (GRB) afterglow. The afterglow spectrum consists of several power-law segments separated by breaks. The image...
Steady-state structure of relativistic collisionless shocks (2000)
We explore analytically the structure of relativistic shock and solitary wave solutions in collisionless plasmas. In the wave frame of reference, a cold plasma is flowing from one end and impacting...
What is the Highest Plausible Redshift of Luminous Quasars? (2000)
The recent discoveries of luminous quasars at high redshifts imply that black holes more massive than a few billion solar masses have been assembled already when the universe was less than a billion...
In the Beginning: The First Sources of Light and the Reionization of the Universe (2000)
Barkana, Rennan, Loeb, Abraham
The formation of the first stars and quasars marks the transformation of the universe from its smooth initial state to its clumpy current state. In popular cosmological models, the first sources of...
The Reionization of the Universe by the First Stars and Quasars (2000)
Loeb, Abraham, Barkana, Rennan
The first light from stars and quasars ended the ``dark ages'' of the universe and led to the reionization of hydrogen by redshift 7. Current observations are at the threshold of probing this epoch....
Does the Mass Accretion Rate Depend On the Radius of the Accreting Star? (2000)
Loeb, Abraham, Narayan, Ramesh, Raymond, John
In some circumstances, the mass accretion rate M^dot onto a compact star may depend not only on external boundary conditions, but also on the radius R of the star. Writing the dependence as a...
Gravitational Microlensing of Gamma-Ray Burst Afterglows by Single and Binary Stars (2000)
We calculate the magnification light curves due to stellar microlensing of gamma-ray burst (GRB) afterglows. A GRB source appears on the sky as a thin ring which expands faster than the speed of...
Emission from Bow Shocks of Beamed Gamma-Ray Bursts (2000)
Beamed gamma-ray burst (GRB) sources produce a bow shock in their gaseous environment. The emitted flux from this bow shock may dominate over the direct emission from the jet for lines of sight which...
Enhanced Microlensing by Stars Around the Black Hole in the Galactic Center (2000)
The effect of stars on the lensing properties of the supermassive black hole in the Galactic Center is similar to the effect of planets on microlensing by a star. We show that the dense stellar...
Bromm, Volker, Kudritzki, Rolf P., Loeb, Abraham
We calculate the generic spectral signature of an early population of massive stars at high redshifts. For metal-free stars in the mass range of 100-1000 solar masses, we find that the combined...
Fluctuations in the Radio Background from Intergalactic Synchrotron Emission (2000)
The shocks produced in the intergalactic medium during large-scale structure formation accelerate a population of highly relativistic electrons which emit synchrotron radiation due to intergalactic...
Gamma-Ray Background from Structure Formation in the Intergalactic Medium (2000)
The universe is filled with a diffuse and isotropic extragalactic background of gamma-ray radiation, containing roughly equal energy flux per decade in photon energy between 3 MeV-100 GeV. The origin...
Expected Number and Flux Distribution of Gamma-Ray-Burst Afterglows with High Redshifts (2000)
Ciardi, Benedetta, Loeb, Abraham
If Gamma-Ray-Bursts (GRBs) occur at high redshifts, then their bright afterglow emission can be used to probe the ionization and metal enrichment histories of the intervening intergalactic medium...
Gravitational Lensing of High Redshift Sources (2000)
Barkana, Rennan, Hogg, David, Loeb, Abraham, Blandford, Roger
The combination of deep exposures and high resolution offered by telescopes in space allows the detection of lensing over a wide range of source redshifts and lens masses. As an example, we model a...
Identifying the Reionization Redshift from the Cosmic Star Formation Rate (2000)
Barkana, Rennan, Loeb, Abraham
We show that the cosmic star formation rate per comoving volume should exhibit a distinct drop around the reionization redshift, when the HII regions in the intergalactic medium around individual...
Escape of Ionizing Radiation from High-Redshift Galaxies (1999)
We use a three-dimensional radiation transfer code to calculate the steady-state escape fraction of ionizing photons from disk galaxies as a function of redshift and galaxy mass. The gaseous disks...
Variability of GRB Afterglows Due to Interstellar Turbulence (1999)
Gamma-Ray Burst (GRB) afterglows are commonly interpreted as synchrotron emission from a relativistic blast wave produced by a point explosion in an ambient medium, plausibly the interstellar medium...
The First Sources of Light in the Universe (1999)
The formation of the first stars and quasars marks the transition between the smooth initial state and the clumpy current state of the Universe. In popular CDM cosmologies, the first sources of light...
Radio Detection of Old GRB Remnants in the Local Universe (1999)
We investigate the hydrodynamic evolution of Gamma--Ray Burst (GRB) remnants at late times (>> 1 year), by extending the standard fireball model into the nonrelativistic Sedov--Taylor regime. We...
Barkana, Rennan, Loeb, Abraham
Direct observations of the first generation of luminous objects will likely become feasible over the next decade. The advent of the Next Generation Space Telescope (NGST) will allow imaging of...
Generation of Magnetic Fields in the Relativistic Shock of Gamma-Ray-Burst Sources (1999)
Medvedev, Mikhail V., Loeb, Abraham
We show that the relativistic two-stream instability can naturally generate strong magnetic fields with 1e-5 - 1e-1 of the equipartition energy density, in the collisionless shocks of Gamma-Ray-Burst...
X-Ray Emission from the First Quasars (1999)
It is currently unknown whether the Universe was reionized by quasars or stars at z>5. We point out that quasars can be best distinguished from stellar systems by their X-ray emission. Based on a...
Identifying Gamma-Ray Burst Remnants in Nearby Galaxies (1999)
Perna, Rosalba, Raymond, John, Loeb, Abraham
We study the spectral signatures arising from cooling and recombination of an interstellar medium whose equilibrium state has been altered over \sim 100 pc by the radiation of a Gamma-Ray Burst (GRB)...
Constraints on Off-Axis X-Ray Emission from Beamed GRBs (1999)
We calculate the prompt x-ray emission as a function of viewing angle for beamed Gamma-Ray Burst (GRB) sources. Prompt x-rays are inevitable due to the less highly blueshifted photons emitted at...
Polarization of the \lya Halos Around Sources Before Cosmological Reionization (1999)
Rybicki, George B., Loeb, Abraham
In Loeb & Rybicki (1999; paper I) it was shown that before reionization, the scattering of \lya photons from a cosmological source might lead to a fairly compact ($\sim 15''$) \lya halo around the...
Probing Red Giant Atmospheres with Gravitational Microlensing (1999)
Heyrovsky, David, Sasselov, Dimitar, Loeb, Abraham
Gravitational microlensing provides a new technique for studying the surfaces of distant stars. Microlensing events are detected in real time and can be followed up with precision photometry and...
Scattered Lyman-alpha Radiation Around Sources Before Cosmological Reionization (1999)
Loeb, Abraham, Rybicki, George
The spectra of the first galaxies and quasars in the Universe should be strongly absorbed shortward of their rest-frame Lyman-alpha wavelength by neutral hydrogen (HI) in the intervening...
The Photo-Evaporation of Dwarf Galaxies During Reionization (1999)
Barkana, Rennan, Loeb, Abraham
During the period of reionization the Universe was filled with a cosmological background of ionizing radiation. By that time a significant fraction of the cosmic gas had already been incorporated...
Constraining the Beaming of Gamma-Ray Bursts With Radio Surveys (1998)
The degree of beaming in Gamma-Ray Bursts (GRBs) is currently unknown. The uncertainty in the gamma-ray beaming angle, theta, leaves the total energy release (proportional to theta^2) and the event...
Semi-analytic models of galaxy formation postulate the existence of virialized gaseous halos around galaxies at high redshifts. A small fraction of the light emitted by any high-redshift quasar is...
A Sub-Relativistic Shock Model for the Radio Emission of SN1998bw (1998)
SN1998bw is the most luminous radio supernova ever observed. Previous discussions argued that its exceptional radio luminosity, 4e38 erg/s, must originate from a highly relativistic shock which is...
Determining the Redshift of Reionization From the Spectra of High-Redshift Sources (1998)
The redshift at which the universe was reionized is currently unknown. We examine the optimal strategy for extracting this redshift, z_{reion}, from the spectra of early sources. For a source located...
The First Stars and Quasars (1998)
The first star clusters and quasars resulted directly from the growth of linear density fluctuations in the early Universe. Since they emerged from a well-defined set of initial conditions, the...
Constraints from the Hubble Deep Field on High Redshift Quasar Models (1998)
Haiman, Zoltan, Madau, Piero, Loeb, Abraham
High resolution, deep imaging surveys are instrumental in setting constraints on semi-analytical structure formation models in Cold Dark Matter (CDM) cosmologies. We show here that the lack of...
Are HI Supershells the Remnants of Gamma-Ray Bursts? (1998)
Gamma-Ray Bursts (GRBs) are thought to originate at cosmological distances from the most powerful explosions in the Universe. If GRBs are not beamed then the distribution of their number as a...
X-Ray Absorption by the Hot Intergalactic Medium (1998)
The current census of observed baryons in the local Universe is still missing a significant fraction of them according to standard Big-Bang nucleosynthesis. Numerical simulations predict that most of...
The Expected Rate of Gamma-Ray Burst Afterglows In Supernova Searches (1998)
We predict the rate at which Gamma-Ray Burst (GRB) afterglows should be detected in supernova searches as a function of limiting flux. Although GRB afterglows are rarer than supernovae, they are...
The redshift of all cosmological sources drifts by a systematic velocity of order a few m/s over a century due to the deceleration of the Universe. The specific functional dependence of the predicted...
Gamma Ray Bursts from Baryon Decay in Neutron Stars (1997)
Pen, Ue-Li, Loeb, Abraham, Turok, Neil
The standard unbroken electroweak theory is known to erase baryon number. The baryon number symmetry can be restored in the core of a neutron star as its density diverges via gravitational...
Effects of Disks on Gravitational Lensing by Spiral Galaxies (1997)
Bartelmann, Matthias, Loeb, Abraham
Gravitational lensing of a quasar by a spiral galaxy should often be accompanied by damped Lyman-alpha absorption and dust extinction due to the intervening gaseous disk. In nearly edge-on...
The discovery of Gamma-Ray Burst (GRB) afterglows revealed a new class of variable sources at optical and radio wavelengths. At present, the environment and precise redshift of the detected...
Spectral Implications of Variability in GRB Fireballs (1997)
Cosmological $\gamma$-ray bursts originate from relativistic winds. Temporal fluctuations in the wind velocity can give rise to internal shocks which dissipate a significant fraction of the wind...
Observational Signatures of the First Quasars (1997)
We study the observational signatures of a potential population of low-luminosity quasars at high redshifts in a LambdaCDM cosmology. We derive the evolution of the quasar luminosity function at...
Emission Spectra from Internal Shocks in Gamma-Ray-Burst Sources (1997)
Unsteady activity of gamma-ray burst sources leads to internal shocks in their emergent relativistic wind. We study the emission spectra from such shocks, assuming that they produce a power-law...
Getting around cosmic variance (1997)
Kamionkowski, Marc, Loeb, Abraham
Cosmic microwave background (CMB) anisotropies probe the primordial density field at the edge of the observable Universe. There is a limiting precision (“cosmic variance”) with which anisotropies...
Microlensing of $\gamma$-Ray Burst Afterglows (1997)
The afterglow of a cosmological Gamma-Ray Burst (GRB) should appear on the sky as a narrow emission ring of radius 3x10^{16}cm(t/day)^{5/8} which expands faster than light. After a day, the ring...
Do the Electrons and Ions in X-ray Clusters Share the Same Temperature? (1997)
The virialization shock around an X-ray cluster primarily heats the ions, since they carry most of the kinetic energy of the infalling gas. Subsequently, the ions share their thermal energy with the...
Probing the Mass Fraction of MACHOs in Extragalactic Halos (1997)
Current microlensing searches calibrate the mass fraction of the Milky Way halo which is in the form of Massive Compact Halo Objects (MACHOs). We show that surveys like the Sloan Digital Sky Survey...
Effects of Dust on Gravitational Lensing by Spiral Galaxies (1997)
Perna, Rosalba, Loeb, Abraham, Bartelmann, Matthias
Gravitational lensing of an optical QSO by a spiral galaxy is often counteracted by dust obscuration, since the line-of-sight to the QSO passes close to the center of the galactic disk. The dust in...
Detection of the First Star Clusters With NGST (1997)
We calculate the observable signatures of the first generation of stars at high redshift (5
The First Stars and Quasars in the Universe (1997)
The transition between the nearly smooth initial state of the Universe and its clumpy state today occurred during the epoch when the first stars and low-luminosity quasars formed. For Cold Dark...
Signatures of Intergalactic Dust From the First Supernovae (1997)
We quantify the consequences of intergalactic dust produced by the first Type II supernovae in the universe. The fraction of gas converted into stars is calibrated based on the observed C/H ratio in...
Getting Around Cosmic Variance (1997)
Kamionkowski, Marc, Loeb, Abraham
Cosmic microwave background (CMB) anisotropies probe the primordial density field at the edge of the observable Universe. There is a limiting precision (``cosmic variance'') with which anisotropies...
Constraints on Galaxy Evolution and the Cosmological Constant From Damped Ly-alpha Absorbers (1997)
We use the existing catalog of Damped Lyman-Alpha (DLA) systems to place constraints on the amount of evolution in the baryonic content of galaxies and on the value of the cosmological constant. The...
Optical Appearance of the Debris of a Star Disrupted by a Massive Black Hole (1997)
We show that the disruption of a star by a 10^6 solar mass black hole in a galactic nucleus could under favorable circumstances produce an optically-thick envelope that radiates with a thermal...
Microlensing of an Elliptical Source by a Point Mass (1997)
Heyrovsky, David, Loeb, Abraham
We present an efficient method for computing lightcurves of an elliptical source which is microlensed by a point mass. The amplification of an extended source involves a two-dimensional integral over...
Formation and Signatures of the First Stars (1997)
We use a spherical hydrodynamics code to show that in cold dark matter cosmologies, the first stars form at z=50 through the direct collapse of gas in low-mass systems (approx 10^4 solar masses)....
Microlensing of Quasars By Stars In Their Damped Lyman alpha Absorbers (1997)
The damped Lyman alpha absorbers (DLAs) in quasar spectra are believed to be the progenitors of present-day disk galaxies. We examine the probability for microlensing of background quasars by stars...
Gravitational Lensing of Quasars by Spiral Galaxies (1997)
Gravitational lensing by a spiral galaxy occurs when the line-of-sight to a background quasar passes within a few kpc from the center of the galactic disk. Since galactic disks are rich in neutral...
Signatures of Stellar Reionization of the Universe (1996)
The high ionization level and universal metallicity (1% solar) of the intergalactic gas at redshifts z10 and damps the amplitude of anisotropies on angular scales 5. The cumulative Bremsstrahlung...
Gravitational Lensing of the X-Ray Background by Clusters of Galaxies (1996)
Refregier, Alexandre, Loeb, Abraham
Gravitational lensing by clusters of galaxies affects the cosmic X-ray background (XRB) by altering the observed density and flux distribution of background X-ray sources. At faint detection flux...
Effect of Gravitational Lensing on Measurements of the Sunyaev-Zel'dovich Effect (1996)
Loeb, Abraham, Refregier, Alexandre
The Sunyaev-Zel'dovich (SZ) effect of a cluster of galaxies is usually measured after background radio sources are removed from the cluster field. Gravitational lensing by the cluster potential leads...
Destruction of Molecular Hydrogen During Cosmological Reionization (1996)
Haiman, Zoltan, Rees, Martin, Loeb, Abraham
We investigate the ability of primordial gas clouds to retain molecular hydrogen (H_2) during the initial phase of the reionization epoch. We find that before the Stromgren spheres of the individual...
Dynamical Mass Estimates of Large-Scale Filaments in Redshift Surveys (1996)
Eisenstein, Daniel J., Loeb, Abraham, Turner, Edwin L.
We propose a new method to measure the mass of large-scale filaments in galaxy redshift surveys. The method is based on the fact that the mass per unit length of isothermal filaments depends only on...
The Lyman-alpha absorption systems observed in the spectra of QSOs are likely to possess bulk peculiar velocities. The free electrons in these systems scatter the microwave background and distort its...
Faraday Rotation of Microwave Background Polarization by a Primordial Magnetic Field (1996)
Loeb, Abraham, Kosowsky, Arthur
The existence of a primordial magnetic field at the last scattering surface may induce a measurable Faraday rotation in the polarization of the cosmic microwave background. We calculate the magnitude...
Probing Cluster Potentials through Gravitational Lensing of Background X-Ray Sources (1995)
Refregier, Alexandre, Loeb, Abraham
We examine the gravitational lensing effect of a foreground galaxy cluster on the number count statistics of background X-ray sources. The lensing produces a deficit in the number of resolved sources...
H_2 Cooling of Primordial Gas Triggered by UV Irradiation (1995)
Haiman, Zoltan, Rees, Martin, Loeb, Abraham
We investigate the formation of molecular hydrogen (H_2) in a primordial H+He gas cloud irradiated by a power-law UV flux. We find that at high densities (>1 cm^{-3}) and low temperatures (
I calculate the contribution of Bremsstrahlung emission from Lyman-alpha absorption clouds to the brightness of the microwave sky. The calculation is based only on the assumption that the clouds...
Cosmological Formation of Low-Mass Objects (1995)
Haiman, Zoltan, Thoul, Anne A., Loeb, Abraham
We investigate the early formation of bound objects with masses comparable to the cosmological Jeans mass (10^5 solar masses). We follow the growth of isolated spherically symmetric density peaks...
Can the Tully-Fisher Relation be the Result of Initial Conditions? (1995)
Eisenstein, Daniel J., Loeb, Abraham
We use Monte Carlo realizations of halo formation histories and a spherical accretion model to calculate the expected scatter in the velocity dispersions of galactic halos of a given mass due to...
GRAVITATIONAL LENSING OF QUASARS BY THEIR DAMPED LYMAN-ALPHA ABSORBERS (1995)
Bartelmann, Matthias, Loeb, Abraham
Damped Lyman-alpha absorbers are believed to be associated with galactic disks. We show that gravitational lensing can therefore affect the statistics of these systems. First, the magnification bias...
Stable and Unstable Accretion Flows with Angular Momentum near a Point Mass (1995)
Ryu, Dongsu, Brown, Garry L., Ostriker, Jeremiah P., Loeb, Abraham
The properties of axisymmetric accretion flows of cold adiabatic gas with zero total energy in the vicinity of a Newtonian point mass are characterized by a single dimensionless parameter, the...
REMOVING DEGENERACY OF MICROLENSING LIGHT CURVES THROUGH NARROW-BAND PHOTOMETRY OF GIANTS (1995)
Loeb, Abraham, Sasselov, Dimitar
The standard light curve of a microlensing event provides only two constraints on the six unknown parameters of the lens. We show that narrow-band photometry during a microlensing event of a giant...
Empirical Constraints on Source Properties and Host Galaxies of Cosmological Gamma-Ray Bursts (1995)
We discuss several constraints on the properties of gamma-ray bursts (GRB) at cosmological distances. First we use the requirement that burst sources must be optically thin to pair production by...
COSMOLOGICAL ORIGIN OF QUASARS (1995)
Quasars are the earliest objects known to exist. We examine their origin in the context of popular models for structure formation in the universe. We show that seeds for quasar black holes could have...
Probing Early Clustering with Lyman-Alpha Absorption Lines Beyond the Quasar Redshift (1994)
Loeb, Abraham, Eisenstein, Daniel J.
Groups and clusters of galaxies hosting a quasar can be found through the detection of Lyman-alpha absorption lines beyond the quasar redshift. The effect occurs whenever the distortion to the...
The central mass distribution of clusters of galaxies can be inferred from gravitationally lensed arcs with known redshifts. For the Abell cluster 2218, this method yields a core mass which is larger...
An Analytical Model for the Triaxial Collapse of Cosmological Perturbations (1994)
Eisenstein, Daniel J., Loeb, Abraham
We present an analytical model for the non-spherical collapse of overdense regions out of a Gaussian random field of initial cosmological perturbations. The collapsing region is treated as an...
Empirical Constraints on Cosmological Gamma-Ray Bursts (1994)
We place empirical constraints on the physical properties of $\gamma-$ray burst events at cosmological distances. In particular we derive probability distributions for the radiation energy...
Origin of Quasar Progenitors from the Collapse of Low-Spin Cosmological Perturbations (1994)
Eisenstein, Daniel J., Loeb, Abraham
We show that seeds for quasar black holes could have originated from the initial cosmological collapse of overdense regions with unusually small rotation. The gas in these rare regions collapses into...
Causality in Strong Shear Flows (1994)
Narayan, Ramesh, Loeb, Abraham, Kumar, Pawan
It is well known that the standard transport equations violate causality when gradients are large or when temporal variations are rapid. We derive a modified set of transport equations that satisfy...
Are Gamma-Ray Bursts at Cosmological Distances Optically-Thin? (1993)
The observed spatial distribution of $\gamma-$ray bursts indicates that they probably originate at cosmological distances. At this distance scale their variability timescale and flux above MeV imply...
Element Diffusion in the Solar Interior (1993)
Thoul, Anne A., Bahcall, John N., Loeb, Abraham
We study the diffusion of helium and other heavy elements in the solar interior by solving exactly the set of flow equations developed by Burgers for a multi-component fluid, including the residual...
Constraints on the Cosmic Rays in the Small Magellanic Cloud (1993)
Dar, Arnon, Laor, Ari, Loeb, Abraham
We show that recent $\gamma$-ray observations of the Small Magellanic Cloud with EGRET rule out a universal cosmic ray flux only at energies below $\approx 10$ GeV, while the observed diffuse X-ray...