Gamma-ray bursts (GRBs) are by far the most powerful explosions in the universe. Over the past two decades, several GRB energy and luminosity correlations were discovered for long gamma-ray bursts, which are bursts wh...Gamma-ray bursts (GRBs) are by far the most powerful explosions in the universe. Over the past two decades, several GRB energy and luminosity correlations were discovered for long gamma-ray bursts, which are bursts whose observed duration exceeds 2 seconds. One important correlation, the Amati relation, involves the observed peak energy, <em>E</em><sub><em>p,obs</em></sub>, in the <em>v</em>F<em><sub>v</sub></em> spectrum and the equivalent isotropic energy, <em>E</em><sub><em>iso</em></sub>. For many years, it was believed that the Amati correlation applied only to long GRBs. In this paper, we use a recent data sample that includes both long and short GRBs to re-examine the issue of whether the Amati correlation applies to long GRBs only. Our results indicate that although short bursts do not follow the Amati relation in the strict sense, they do exhibit a correlation between the intrinsic peak energy, <em>E</em><em><sub>p,i</sub></em>, and <em>E<sub>iso</sub></em> that is very similar to the Amati relation but with a different normalization and slope. The paper also discusses the physical interpretation of this correlation in the context of the internal shock model.展开更多
Gamma-ray bursts (GRBs) are the most intense and powerful explosions in the universe. Based on their observed duration, they are traditionally divided into long bursts whose observed duration equals or exceeds 2 s, an...Gamma-ray bursts (GRBs) are the most intense and powerful explosions in the universe. Based on their observed duration, they are traditionally divided into long bursts whose observed duration equals or exceeds 2 s, and short bursts whose observed duration is less than 2 s. Several GRB energy and luminosity correlations have been discovered for long gamma-ray bursts. Two important correlations are the Amati relation and the Yonetoku relation. The Amati relation is a correlation between the intrinsic peak energy, E<sub>p</sub><sub>,i</sub>, obtained from the νF<sub>ν</sub> spectrum and the equivalent isotropic energy, E<sub>iso</sub>, while the Yonetoku relation is a correlation between E<sub>p,i</sub> and the peak isotropic luminosity, L<sub>iso</sub>. In this paper, we use a recent data sample that includes both long and short GRBs to compare these two correlations for the two groups of bursts. We also compare the E<sub>iso</sub>-L<sub>iso</sub> plane for these two types of bursts. Our results indicate that both long and short bursts adhere to these two correlations but with different normalizations. We also find that the E<sub>iso</sub>-L<sub>iso</sub> plane is similar for both types of GRBs but is shifted to lower values of E<sub>iso</sub> for short GRBs.展开更多
The Amati and Yonetoku relations are two of the main energy and luminosity correlations that currently exist for gamma-ray bursts (GRBs). The Amati relation is a correlation between the intrinsic peak energy, Epeak, i...The Amati and Yonetoku relations are two of the main energy and luminosity correlations that currently exist for gamma-ray bursts (GRBs). The Amati relation is a correlation between the intrinsic peak energy, Epeak, in the vFv spectrum of a burst and its equivalent isotropic energy, Eiso. The Yonetoku relation is a correlation between Epeak and the isotropic peak luminosity, Liso. In this paper, we use a recent data sample of 65 GRBs to investigate whether these two relations evolve with redshift, z. The z-correction and the?k-correction are both taken into account. Our method consists of binning the data in redshift, z, then applying (for each bin) a fit of the form:?log(Eiso) = A + Blog(Epeak/Epeak>) for the Amati relation, and of the form:?log(Liso) = A + Blog(Epeak/Epeak>) for the Yonetoku relation, where Epeak> is the mean value of the peak energy for the entire sample. The objective is to see whether the two fitting parameters, A and B, evolve systematically with z. Good least-squares fits were obtained with reasonable values for the linear regression coefficient, r. Our results indicate that the normalization, A, and the slope, B, do not evolve with redshift, and hence the Amati and Yonetoku relations seem to be redshift independent.展开更多
Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. Over the past two decades, several GRB energy and luminosity correlations were discovered. These correlations typically involve an observable p...Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. Over the past two decades, several GRB energy and luminosity correlations were discovered. These correlations typically involve an observable parameter, like the observed peak energy, Ep,obs, and a non-observable quantity, like the equivalent isotropic energy, Eiso. This paper provides a brief review of GRB peak energy correlations. Specifically, it focuses on the Amati relation, which correlates Ep,obs and Eiso, and the Ghirlanda relation, which correlates Ep,obs and Ey, the total energy corrected for beaming. The paper also discusses the physical interpretation of these relations in the context of the internal shock model.展开更多
Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. Alt-hough the exact mechanism behind these explosions remains elusive, GRBs hold great promise as cosmological probes for two main reasons: the...Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. Alt-hough the exact mechanism behind these explosions remains elusive, GRBs hold great promise as cosmological probes for two main reasons: they have been observed up to very high redshift (z > 9), and their gamma-ray emission is unencumbered by any intervening dust. Several GRB energy and luminosity indicators have been discovered. These indicators correlate an observable quantity, like the intrinsic peak energy, E<sub>p</sub>,<sub>i</sub>, in the spectrum of a burst to an unobservable parameter like the equivalent isotropic energy, E<sub>iso</sub>, or the isotropic peak luminosity, L<sub>p,iso</sub>. This paper provides a brief review of one of these energy and luminosity indicators, the Amati relation, and discusses its potential use as a cosmological probe.展开更多
Gamma-ray bursts (GRBs) are the most powerful events in the universe, and are promising standard candles for cosmological studies. The data from NASA's Swift satellite reveal a distribution for the GRB number dens...Gamma-ray bursts (GRBs) are the most powerful events in the universe, and are promising standard candles for cosmological studies. The data from NASA's Swift satellite reveal a distribution for the GRB number density that peaks at a redshift between 1 and 3. In this paper, we classify GRBs based on their duration and discuss the origin of their progenitors. We shed light on the formation mechanism of supermassive black holes and massive stars at the early universe, and show how this process and other related events can lead to a relatively high number of GRBs that peak at high redshift.展开更多
The recent discovery of gravitational waves has revolutionized our understanding of many aspects regarding how the universe works. The formation of galaxies stands as one of the most challenging problems in astrophysi...The recent discovery of gravitational waves has revolutionized our understanding of many aspects regarding how the universe works. The formation of galaxies stands as one of the most challenging problems in astrophysics. Regardless of how far back we look in the early universe, we keep discovering galaxies with supermassive black holes lurking at their centers. Many models have been proposed to explain the rapid formation of supermassive black holes, including the massive accretion of material, the collapse of type III stars, and the merger of stellar mass black holes. Some of these events give rise to the production of gravitational waves that could be detected by future generations of more sensitive detectors. Alternatively, the existence of these supermassive black holes can be explained in the context of primordial black holes. In this paper we discuss the various models of galaxy formation shedding light on the role that gravitational waves can play to test of the validity of some of these models. We also discuss the prospect of primordial black holes as a seeding constituent for galaxy formation.展开更多
The discovery of gravitational waves resulting from the merger of two massive black holes (GW150914) has revolutionized our view of merging compact binaries. Recently, the Swope Supernova Survey of the optical counter...The discovery of gravitational waves resulting from the merger of two massive black holes (GW150914) has revolutionized our view of merging compact binaries. Recently, the Swope Supernova Survey of the optical counterpart of a gravitational wave event in the NGC 4993 galaxy, GW170817, emanating from the merger of two neutron stars, has triggered a lot of research work. Emphasis has been on comparing the existing theoretical models with the observational data, allowing for the prospect of an even more stringent test of general relativity. The afterglow of this event was observed in a wide range of wavelengths extending from radio waves to gamma rays. In this work, we first explore the evolutionary pathways of compact binary systems following the in-spiral, merger, and ring down sequence. We then proceed to discuss the processes leading to the production of gravitational waves and electromagnetic emission resulting from the merger of compact objects, particularly neutron star binaries and neutron star-black hole systems. We construct a basic inventory of the energy released during the merger of compact binaries in all bands of the electromagnetic spectrum with emphasis on gamma-ray burst emission. The constraints on certain wavelength emissions, such as gamma-ray bursts, are discussed in terms of orbital dynamical instabilities, energy transfer processes, and possible jet orientations with respect to the observer. Finally, we explore the futuristic perspective of the impact of gravitational waves detection on our understanding of the working of the universe.展开更多
Observational evidence reveals that supermassive black holes reside at the center of most galaxies up to the furthest observable redshifts. The tight M-σ relation suggests a close operative feedback between the growt...Observational evidence reveals that supermassive black holes reside at the center of most galaxies up to the furthest observable redshifts. The tight M-σ relation suggests a close operative feedback between the growth of supermassive black holes and the growth of the galactic bulge. Models describing the formation scenarios of seeding black holes and their growth are reviewed. In each of these models, the prevailing environments in the primordial-galactic disks, including the gas dynamics, cooling processes, and metallic enrichment are explored. It is shown that the galactic disk parameters set constraints on the channel of formation of the seeding black holes and their growth. Primordial black holes from the inflationary era, their formation, possible interaction, and constraints on their observations are discussed. Gamma-ray bursts resulting either from the collapse of massive stars, or from the collision of compact objects are explored. The abundance of these violent events in the early universe suggests a possible connection with galaxy formation.展开更多
The lag-luminosity relation for gamma-ray bursts (GRBs) is an anti-correlation between the time lag, ?lag, which represents the delay between the arrival of hard and soft photons, and the isotropic peak luminosity, L....The lag-luminosity relation for gamma-ray bursts (GRBs) is an anti-correlation between the time lag, ?lag, which represents the delay between the arrival of hard and soft photons, and the isotropic peak luminosity, L. In this paper, we use a sample of 43 Swift bursts, which was taken from Ukwatta et al., to investigate whether this relation depends on redshift. Both the z-correction and the k-correction are taken into account. Our analysis consists of binning the data in redshift, z, then applying a fit of the form: for each bin, where ?lag0 is the time-lag in the burst’s source frame, and is the corresponding mean value for the entire sample. The goal is to see whether the two fitting parameters, A and B, evolve in a systematic way with z. Our results indicate that both the normalization, A, and the slope, B, seem to vary in a systematic way with redshift. We note that although good best-fits were obtained, with reasonable values for both the linear regression coefficient, r, and the reduced chi-squared, the data showed large scatter. Also, the number of GRBs in the sample studied is not large, and thus our conclusions are only tentative at this point. A flat universe with M = 0.27, ?? = 0.73, and a Hubble constant, H0 = 70 km.s-1.Mpc-1 is assumed.展开更多
Dark matter was first suspected in clusters of galaxies when these galaxies were found to move with too high a speed to be retained in the cluster by their gravitational influence on each other. Some current theories ...Dark matter was first suspected in clusters of galaxies when these galaxies were found to move with too high a speed to be retained in the cluster by their gravitational influence on each other. Some current theories favor cold dark matter models where particles are created with low velocity dispersions and thus would become trapped in baryonic gravitational potentials. According to the standard Big-Bang model, dark matter is of nonbaryonic origin, otherwise the observed abundance of helium in the Universe would be violated. In this work, recent theoretical and observational developments are used to form a consistent picture of the events in the early Universe that gave rise to dark matter. According to the model that will be presented in this paper, supersymmetry plays a major role. In addition, the possibility that dark matter evolves in a spacetime manifold different from that of the observed Universe is discussed.展开更多
Supernovae are powerful explosions of massive stars that have reached a terminal stage in their evolution. A huge amount of energy is released during the explosion in a wide range of wavelengths. The supernova explosi...Supernovae are powerful explosions of massive stars that have reached a terminal stage in their evolution. A huge amount of energy is released during the explosion in a wide range of wavelengths. The supernova explosion causes a sudden rise in the dead star’s luminosity which may outshine momentarily the entire galaxy in which it resides. The explosion is produced by a catastrophic collapse of the iron core of a massive star or the collapse of a white dwarf after accreting enough mass from its companion to reach the Chandrasekhar limit. The first record of a supernova occurrence goes back to 185 CE. Subsequently, humans have witnessed across the centuries a series of such violent events that appear suddenly in the sky and illuminate the darkness of the night for several weeks or months. In the first part of this paper, we briefly describe the processes that lead to a supernova explosion. In the second part, we discuss historical supernovae as appearing in the records of human civilizations. In the third part, we highlight ancient records relating the sudden appearance of a supernova or a comet to the spread of epidemics in certain regions of the world.展开更多
The gravitational signature of antimatter has received growing interest during the past few decades. Much of the theoretical work in ordinary tensor gravity rules out any difference in the gravitational interaction of...The gravitational signature of antimatter has received growing interest during the past few decades. Much of the theoretical work in ordinary tensor gravity rules out any difference in the gravitational interaction of matter and antimatter. Fundamental principles and theoretical models describing the nature of matter and antimatter are reviewed. The implication of a probable repulsive field between matter and antimatter and its far reaching consequences on certain cosmic issues, such as the early phase of the Big Bang, the Hawking radiation, virtual particle production and annihilations, are discussed. Experiments designed to probe the gravitational signature of antimatter are reviewed, and a new space-borne experiment to probe the nature of matter-antimatter interactions is proposed.展开更多
Gamma-ray bursts (GRBs) are extremely powerful explosions that have been traditionally classified into two categories: long bursts (LGRBs) with an observed duration T<sub>90 </sub>> 2 s, and short burst...Gamma-ray bursts (GRBs) are extremely powerful explosions that have been traditionally classified into two categories: long bursts (LGRBs) with an observed duration T<sub>90 </sub>> 2 s, and short bursts (SGRBs) with an observed duration T<sub>90</sub> T<sub>90</sub> is the time interval during which 90% of the fluence is detected. LGRBs are believed to emanate from the core-collapse of massive stars, while SGRBs are believed to result from the merging of two compact objects, like two neutron stars. Because LGRBs are produced by the violent death of massive stars, we expect that their redshift distribution should trace the star-formation rate (SFR). The purpose of our study is to investigate the extent to which the redshift distribution of LGRBs follows and reflects the SFR. We use a sample of 370 LGRBs taken from the Swift catalog, and we investigate different models for the LGRB redshift distribution. We also carry out Monte Carlo simulations to check the consistency of our results. Our results indicate that the SFR can describe the LGRB redshift distribution well for high redshift bursts, but it needs an evolution term to fit the distribution well at low redshift.展开更多
Gamma-ray bursts (GRBs) are violent stellar explosions that are traditionally divided into two groups: short bursts (SGRBs) with an observed duration T90 T90 > 2 s, where T90 refers to the time needed for 90% of th...Gamma-ray bursts (GRBs) are violent stellar explosions that are traditionally divided into two groups: short bursts (SGRBs) with an observed duration T90 T90 > 2 s, where T90 refers to the time needed for 90% of the fluence to be detected. Studies of progenitor models suggest that LGRBs emanate from the core collapse of massive stars, while SGRBs result from the merging of two compact objects, like two neutron stars or a neutron star and a black hole. Recent studies have found evidence that there is an anticorrelation between the intrinsic duration and the redshift of long GRBs. In this study, we first check whether LGRBs exhibit an anticorrelation between their intrinsic duration and redshift using an expanded dataset of long bursts that we have compiled. Next, we investigate whether this anticorrelation applies to SGRBs as well using a sample of short GRBs that we have compiled. Our analysis confirms the results obtained by previous studies regarding the anticorrelation for LGRBs. On the other hand, our results indicate that short GRBs do not exhibit such an anticorrelation. We discuss the implications of our results in the context of how metallicity evolves with redshift and the role that it might play in the aforementioned anticorrelation.展开更多
文摘Gamma-ray bursts (GRBs) are by far the most powerful explosions in the universe. Over the past two decades, several GRB energy and luminosity correlations were discovered for long gamma-ray bursts, which are bursts whose observed duration exceeds 2 seconds. One important correlation, the Amati relation, involves the observed peak energy, <em>E</em><sub><em>p,obs</em></sub>, in the <em>v</em>F<em><sub>v</sub></em> spectrum and the equivalent isotropic energy, <em>E</em><sub><em>iso</em></sub>. For many years, it was believed that the Amati correlation applied only to long GRBs. In this paper, we use a recent data sample that includes both long and short GRBs to re-examine the issue of whether the Amati correlation applies to long GRBs only. Our results indicate that although short bursts do not follow the Amati relation in the strict sense, they do exhibit a correlation between the intrinsic peak energy, <em>E</em><em><sub>p,i</sub></em>, and <em>E<sub>iso</sub></em> that is very similar to the Amati relation but with a different normalization and slope. The paper also discusses the physical interpretation of this correlation in the context of the internal shock model.
文摘Gamma-ray bursts (GRBs) are the most intense and powerful explosions in the universe. Based on their observed duration, they are traditionally divided into long bursts whose observed duration equals or exceeds 2 s, and short bursts whose observed duration is less than 2 s. Several GRB energy and luminosity correlations have been discovered for long gamma-ray bursts. Two important correlations are the Amati relation and the Yonetoku relation. The Amati relation is a correlation between the intrinsic peak energy, E<sub>p</sub><sub>,i</sub>, obtained from the νF<sub>ν</sub> spectrum and the equivalent isotropic energy, E<sub>iso</sub>, while the Yonetoku relation is a correlation between E<sub>p,i</sub> and the peak isotropic luminosity, L<sub>iso</sub>. In this paper, we use a recent data sample that includes both long and short GRBs to compare these two correlations for the two groups of bursts. We also compare the E<sub>iso</sub>-L<sub>iso</sub> plane for these two types of bursts. Our results indicate that both long and short bursts adhere to these two correlations but with different normalizations. We also find that the E<sub>iso</sub>-L<sub>iso</sub> plane is similar for both types of GRBs but is shifted to lower values of E<sub>iso</sub> for short GRBs.
文摘The Amati and Yonetoku relations are two of the main energy and luminosity correlations that currently exist for gamma-ray bursts (GRBs). The Amati relation is a correlation between the intrinsic peak energy, Epeak, in the vFv spectrum of a burst and its equivalent isotropic energy, Eiso. The Yonetoku relation is a correlation between Epeak and the isotropic peak luminosity, Liso. In this paper, we use a recent data sample of 65 GRBs to investigate whether these two relations evolve with redshift, z. The z-correction and the?k-correction are both taken into account. Our method consists of binning the data in redshift, z, then applying (for each bin) a fit of the form:?log(Eiso) = A + Blog(Epeak/Epeak>) for the Amati relation, and of the form:?log(Liso) = A + Blog(Epeak/Epeak>) for the Yonetoku relation, where Epeak> is the mean value of the peak energy for the entire sample. The objective is to see whether the two fitting parameters, A and B, evolve systematically with z. Good least-squares fits were obtained with reasonable values for the linear regression coefficient, r. Our results indicate that the normalization, A, and the slope, B, do not evolve with redshift, and hence the Amati and Yonetoku relations seem to be redshift independent.
文摘Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. Over the past two decades, several GRB energy and luminosity correlations were discovered. These correlations typically involve an observable parameter, like the observed peak energy, Ep,obs, and a non-observable quantity, like the equivalent isotropic energy, Eiso. This paper provides a brief review of GRB peak energy correlations. Specifically, it focuses on the Amati relation, which correlates Ep,obs and Eiso, and the Ghirlanda relation, which correlates Ep,obs and Ey, the total energy corrected for beaming. The paper also discusses the physical interpretation of these relations in the context of the internal shock model.
文摘Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. Alt-hough the exact mechanism behind these explosions remains elusive, GRBs hold great promise as cosmological probes for two main reasons: they have been observed up to very high redshift (z > 9), and their gamma-ray emission is unencumbered by any intervening dust. Several GRB energy and luminosity indicators have been discovered. These indicators correlate an observable quantity, like the intrinsic peak energy, E<sub>p</sub>,<sub>i</sub>, in the spectrum of a burst to an unobservable parameter like the equivalent isotropic energy, E<sub>iso</sub>, or the isotropic peak luminosity, L<sub>p,iso</sub>. This paper provides a brief review of one of these energy and luminosity indicators, the Amati relation, and discusses its potential use as a cosmological probe.
文摘Gamma-ray bursts (GRBs) are the most powerful events in the universe, and are promising standard candles for cosmological studies. The data from NASA's Swift satellite reveal a distribution for the GRB number density that peaks at a redshift between 1 and 3. In this paper, we classify GRBs based on their duration and discuss the origin of their progenitors. We shed light on the formation mechanism of supermassive black holes and massive stars at the early universe, and show how this process and other related events can lead to a relatively high number of GRBs that peak at high redshift.
文摘The recent discovery of gravitational waves has revolutionized our understanding of many aspects regarding how the universe works. The formation of galaxies stands as one of the most challenging problems in astrophysics. Regardless of how far back we look in the early universe, we keep discovering galaxies with supermassive black holes lurking at their centers. Many models have been proposed to explain the rapid formation of supermassive black holes, including the massive accretion of material, the collapse of type III stars, and the merger of stellar mass black holes. Some of these events give rise to the production of gravitational waves that could be detected by future generations of more sensitive detectors. Alternatively, the existence of these supermassive black holes can be explained in the context of primordial black holes. In this paper we discuss the various models of galaxy formation shedding light on the role that gravitational waves can play to test of the validity of some of these models. We also discuss the prospect of primordial black holes as a seeding constituent for galaxy formation.
文摘The discovery of gravitational waves resulting from the merger of two massive black holes (GW150914) has revolutionized our view of merging compact binaries. Recently, the Swope Supernova Survey of the optical counterpart of a gravitational wave event in the NGC 4993 galaxy, GW170817, emanating from the merger of two neutron stars, has triggered a lot of research work. Emphasis has been on comparing the existing theoretical models with the observational data, allowing for the prospect of an even more stringent test of general relativity. The afterglow of this event was observed in a wide range of wavelengths extending from radio waves to gamma rays. In this work, we first explore the evolutionary pathways of compact binary systems following the in-spiral, merger, and ring down sequence. We then proceed to discuss the processes leading to the production of gravitational waves and electromagnetic emission resulting from the merger of compact objects, particularly neutron star binaries and neutron star-black hole systems. We construct a basic inventory of the energy released during the merger of compact binaries in all bands of the electromagnetic spectrum with emphasis on gamma-ray burst emission. The constraints on certain wavelength emissions, such as gamma-ray bursts, are discussed in terms of orbital dynamical instabilities, energy transfer processes, and possible jet orientations with respect to the observer. Finally, we explore the futuristic perspective of the impact of gravitational waves detection on our understanding of the working of the universe.
文摘Observational evidence reveals that supermassive black holes reside at the center of most galaxies up to the furthest observable redshifts. The tight M-σ relation suggests a close operative feedback between the growth of supermassive black holes and the growth of the galactic bulge. Models describing the formation scenarios of seeding black holes and their growth are reviewed. In each of these models, the prevailing environments in the primordial-galactic disks, including the gas dynamics, cooling processes, and metallic enrichment are explored. It is shown that the galactic disk parameters set constraints on the channel of formation of the seeding black holes and their growth. Primordial black holes from the inflationary era, their formation, possible interaction, and constraints on their observations are discussed. Gamma-ray bursts resulting either from the collapse of massive stars, or from the collision of compact objects are explored. The abundance of these violent events in the early universe suggests a possible connection with galaxy formation.
文摘The lag-luminosity relation for gamma-ray bursts (GRBs) is an anti-correlation between the time lag, ?lag, which represents the delay between the arrival of hard and soft photons, and the isotropic peak luminosity, L. In this paper, we use a sample of 43 Swift bursts, which was taken from Ukwatta et al., to investigate whether this relation depends on redshift. Both the z-correction and the k-correction are taken into account. Our analysis consists of binning the data in redshift, z, then applying a fit of the form: for each bin, where ?lag0 is the time-lag in the burst’s source frame, and is the corresponding mean value for the entire sample. The goal is to see whether the two fitting parameters, A and B, evolve in a systematic way with z. Our results indicate that both the normalization, A, and the slope, B, seem to vary in a systematic way with redshift. We note that although good best-fits were obtained, with reasonable values for both the linear regression coefficient, r, and the reduced chi-squared, the data showed large scatter. Also, the number of GRBs in the sample studied is not large, and thus our conclusions are only tentative at this point. A flat universe with M = 0.27, ?? = 0.73, and a Hubble constant, H0 = 70 km.s-1.Mpc-1 is assumed.
文摘Dark matter was first suspected in clusters of galaxies when these galaxies were found to move with too high a speed to be retained in the cluster by their gravitational influence on each other. Some current theories favor cold dark matter models where particles are created with low velocity dispersions and thus would become trapped in baryonic gravitational potentials. According to the standard Big-Bang model, dark matter is of nonbaryonic origin, otherwise the observed abundance of helium in the Universe would be violated. In this work, recent theoretical and observational developments are used to form a consistent picture of the events in the early Universe that gave rise to dark matter. According to the model that will be presented in this paper, supersymmetry plays a major role. In addition, the possibility that dark matter evolves in a spacetime manifold different from that of the observed Universe is discussed.
文摘Supernovae are powerful explosions of massive stars that have reached a terminal stage in their evolution. A huge amount of energy is released during the explosion in a wide range of wavelengths. The supernova explosion causes a sudden rise in the dead star’s luminosity which may outshine momentarily the entire galaxy in which it resides. The explosion is produced by a catastrophic collapse of the iron core of a massive star or the collapse of a white dwarf after accreting enough mass from its companion to reach the Chandrasekhar limit. The first record of a supernova occurrence goes back to 185 CE. Subsequently, humans have witnessed across the centuries a series of such violent events that appear suddenly in the sky and illuminate the darkness of the night for several weeks or months. In the first part of this paper, we briefly describe the processes that lead to a supernova explosion. In the second part, we discuss historical supernovae as appearing in the records of human civilizations. In the third part, we highlight ancient records relating the sudden appearance of a supernova or a comet to the spread of epidemics in certain regions of the world.
文摘The gravitational signature of antimatter has received growing interest during the past few decades. Much of the theoretical work in ordinary tensor gravity rules out any difference in the gravitational interaction of matter and antimatter. Fundamental principles and theoretical models describing the nature of matter and antimatter are reviewed. The implication of a probable repulsive field between matter and antimatter and its far reaching consequences on certain cosmic issues, such as the early phase of the Big Bang, the Hawking radiation, virtual particle production and annihilations, are discussed. Experiments designed to probe the gravitational signature of antimatter are reviewed, and a new space-borne experiment to probe the nature of matter-antimatter interactions is proposed.
文摘Gamma-ray bursts (GRBs) are extremely powerful explosions that have been traditionally classified into two categories: long bursts (LGRBs) with an observed duration T<sub>90 </sub>> 2 s, and short bursts (SGRBs) with an observed duration T<sub>90</sub> T<sub>90</sub> is the time interval during which 90% of the fluence is detected. LGRBs are believed to emanate from the core-collapse of massive stars, while SGRBs are believed to result from the merging of two compact objects, like two neutron stars. Because LGRBs are produced by the violent death of massive stars, we expect that their redshift distribution should trace the star-formation rate (SFR). The purpose of our study is to investigate the extent to which the redshift distribution of LGRBs follows and reflects the SFR. We use a sample of 370 LGRBs taken from the Swift catalog, and we investigate different models for the LGRB redshift distribution. We also carry out Monte Carlo simulations to check the consistency of our results. Our results indicate that the SFR can describe the LGRB redshift distribution well for high redshift bursts, but it needs an evolution term to fit the distribution well at low redshift.
文摘Gamma-ray bursts (GRBs) are violent stellar explosions that are traditionally divided into two groups: short bursts (SGRBs) with an observed duration T90 T90 > 2 s, where T90 refers to the time needed for 90% of the fluence to be detected. Studies of progenitor models suggest that LGRBs emanate from the core collapse of massive stars, while SGRBs result from the merging of two compact objects, like two neutron stars or a neutron star and a black hole. Recent studies have found evidence that there is an anticorrelation between the intrinsic duration and the redshift of long GRBs. In this study, we first check whether LGRBs exhibit an anticorrelation between their intrinsic duration and redshift using an expanded dataset of long bursts that we have compiled. Next, we investigate whether this anticorrelation applies to SGRBs as well using a sample of short GRBs that we have compiled. Our analysis confirms the results obtained by previous studies regarding the anticorrelation for LGRBs. On the other hand, our results indicate that short GRBs do not exhibit such an anticorrelation. We discuss the implications of our results in the context of how metallicity evolves with redshift and the role that it might play in the aforementioned anticorrelation.
