We identify an S-shaped main-jet axis in the Vela core-collapse supernova remnant(CCSNR)that we attribute to a pair of precessing jets,one of the tens of pairs of jets that exploded the progenitor of Vela according to...We identify an S-shaped main-jet axis in the Vela core-collapse supernova remnant(CCSNR)that we attribute to a pair of precessing jets,one of the tens of pairs of jets that exploded the progenitor of Vela according to the jittering jets explosion mechanism(JJEM).A main-jet axis is a symmetry axis across the CCSNR and through the center.We identify the S-shaped main-jet axis by the high abundance of ejecta elements,oxygen,neon,and magnesium.We bring the number of identified pairs of clumps and ears in Vela to seven,two pairs shaped by the pair of precessing jets that formed the main-jet axis.The pairs and the main-jet axis form the point-symmetric wind-rose structure of Vela.The other five pairs of clumps/ears do not have signatures near the center,only on two opposite sides of the CCSNR.We discuss different possible jet-less shaping mechanisms to form such a point-symmetric morphology and dismiss these processes because they cannot explain the point-symmetric morphology of Vela,the S-shaped high ejecta abundance pattern,and the enormous energy required to shape the S-shaped structure.Our findings strongly support the JJEM and further severely challenge the neutrino-driven explosion mechanism.展开更多
With a one-dimensional stellar evolution model,we find that massive main sequence stars can accrete mass at very high mass accretion rates without expanding much if they lose a significant fraction of this mass from t...With a one-dimensional stellar evolution model,we find that massive main sequence stars can accrete mass at very high mass accretion rates without expanding much if they lose a significant fraction of this mass from their outer layers simultaneously with mass accretion.We assume the accretion process is via an accretion disk that launches powerful jets from its inner zones.These jets remove the outer high-entropy layers of the mass-accreting star.This process operates in a negative feedback cycle,as the jets remove more envelope mass when the star expands.With the one-dimensional model,we mimic the mass removal by jets by alternating mass addition and mass removal phases.For the simulated models of 30M☉and 60M☉,the star does not expand much if we remove more than about half of the added mass in not-too-short episodes.This holds even if we deposit the energy the jets do not carry into the envelope.As the star does not expand much,its gravitational potential well stays deep,and the jets are energetic.These results are relevant to bright transient events of binary systems powered by accretion and the launching of jets,e.g.,intermediate luminosity optical transients,including some luminous red novae,the grazing envelope evolution,and the 1837–1856 Great Eruption of Eta Carinae.展开更多
We use a simple dynamical scheme to simulate the ejecta of type Ⅰa supernova(SN Ia) scenarios with two exploding white dwarfs(WDs) and find that the velocity distribution of the ejecta has difficulties accounting for...We use a simple dynamical scheme to simulate the ejecta of type Ⅰa supernova(SN Ia) scenarios with two exploding white dwarfs(WDs) and find that the velocity distribution of the ejecta has difficulties accounting for bimodal emission line profiles with a large separation between the two emission peaks.The essence of the dynamical code is in including the fact that the ejecta does not leave the system instantaneously.We find that the final separation velocity between the centers of masses of the two WDs' ejecta is ≃80% of the pre-explosion WDs' orbital velocity,i.e.,we find separation velocities of 4200-5400 km s^(-1) for two WDs of masses M_(1)=M_(2)=0.94 M⊙.The lower separation velocities we find challenge scenarios with two exploding WDs to explain bimodal emission line profiles with observed velocity separations of up to ≃7000 km s^(-1).Only the mass in the ejecta of one WD with an explosion velocity lower than the separation velocity contributes to one peak of the bimodal profile;this is the inner ejecta.We find the inner ejecta to be only≲15% of the ejecta mass in energetic explosions.Less energetic explosions yield higher inner mass but lower separation velocities.We encourage searching for alternative explanations of bimodal line profiles.展开更多
Moirésuperlattices hosting flat bands and correlated states have become a central focus in condensed matter research.Using first-principles calculations,we investigate three-dimensional flat bands in alternating ...Moirésuperlattices hosting flat bands and correlated states have become a central focus in condensed matter research.Using first-principles calculations,we investigate three-dimensional flat bands in alternating twisted NbSe_(2)moirébulk structures,which exhibit stronger interlayer interactions than twisted bilayer configurations.Our results show that moirébulks undergo spontaneous large-scale structural relaxation,leading to the formation of remarkably flat energy bands at twist angles≤7.31°.The k_(z)-dependent dispersion of these flat bands across different moirébulks highlights their intrinsic three-dimensional character.Moreover,the presence of out-of-plane mirror symmetry in these moirébulk structures indicates potential interlayer triplet superconducting pairing mechanisms,distinct from those in twisted bilayer systems.This work opens new avenues for exploring three-dimensional flat bands in other moirébulk systems.展开更多
I review studies of core collapse supernovae(CCSNe) and similar transient events that attribute major roles to jets in powering most CCSNe and in shaping their ejecta. I start with reviewing the jittering jets explosi...I review studies of core collapse supernovae(CCSNe) and similar transient events that attribute major roles to jets in powering most CCSNe and in shaping their ejecta. I start with reviewing the jittering jets explosion mechanism that I take to power most CCSN explosions. Neutrino heating does play a role in boosting the jets. I compare the morphologies of some CCSN remnants to planetary nebulae to conclude that jets and instabilities are behind the shaping of their ejecta. I then discuss CCSNe that are descendants of rapidly rotating collapsing cores that result in fixed-axis jets(with small jittering) that shape bipolar ejecta. A large fraction of the bipolar CCSNe are superluminous supernovae(SLSNe). I conclude that modeling of SLSN light curves and bumps in the light curves must include jets, even when considering energetic magnetars and/or ejecta interaction with the circumstellar matter(CSM). I connect the properties of bipolar CCSNe to common envelope jets supernovae(CEJSNe) where an old neutron star or a black hole spirals-in inside the envelope and then inside the core of a red supergiant. I discuss how jets can shape the pre-explosion CSM, as in Supernova 1987A, and can power pre-explosion outbursts(precursors)in binary system progenitors of CCSNe and CEJSNe. Binary interaction also facilitates the launching of postexplosion jets.展开更多
We follow the premise that most intermediate luminosity optical transients （ILOTs） are powered by rapid mass accretion onto a main sequence star, and study the effects of jets launched by an accretion disk. The disk...We follow the premise that most intermediate luminosity optical transients （ILOTs） are powered by rapid mass accretion onto a main sequence star, and study the effects of jets launched by an accretion disk. The disk is formed due to large specific angular momentum of the accreted mass. The two opposite jets might expel some of the mass from the reservoir of gas that feeds the disk, and therefore reduce and shorten the mass accretion process. We argue that by this process ILOTs limit their luminosity and might even shut themselves off in this negative jet feedback mechanism （JFM）. The group of ILOTs is a new member of a large family of astrophysical objects whose activity is regulated by the operation of the JFM.展开更多
I build a toy model in the frame of the jittering jets explosion mechanism(JJEM)of core collapse supernovae that incorporates both the stochastically varying angular momentum component of the material that the newly b...I build a toy model in the frame of the jittering jets explosion mechanism(JJEM)of core collapse supernovae that incorporates both the stochastically varying angular momentum component of the material that the newly born neutron star(NS)accretes and the constant angular momentum component,and show that the JJEM can account for the≃2.5–5M⊙mass gap between NSs and black holes(BHs).The random component of the angular momentum results from pre-collapse core convection fluctuations that are amplified by post-collapse instabilities.The fixed angular momentum component results from pre-collapse core rotation.For slowly rotating pre-collapse cores the stochastic angular momentum fluctuations form intermittent accretion disks(or belts)around the NS with varying angular momentum axes in all directions.The intermittent accretion disk/belt launches jets in all directions that expel the core material in all directions early on,hence leaving an NS remnant.Rapidly rotating pre-collapse cores form an accretion disk with angular momentum axis that is about the same as the pre-collapse core rotation.The NS launches jets along this axis and hence the jets avoid the equatorial plane region.Inflowing core material continues to feed the central object from the equatorial plane increasing the NS mass to form a BH.The narrow transition from slow to rapid pre-collapse core rotation,i.e.,from an efficient to inefficient jet feedback mechanism,accounts for the sparsely populated mass gap.展开更多
I consider a flow structure by which main sequence companions that enter a common envelope evolution(CEE)with giant stars might launch jets even when the accreted gas has a sub-Keplerian specific angular momentum.I fi...I consider a flow structure by which main sequence companions that enter a common envelope evolution(CEE)with giant stars might launch jets even when the accreted gas has a sub-Keplerian specific angular momentum.I first show that after a main sequence star enters the envelope of a giant star the specific angular momentum of the accreted gas is sub-Keplerian but still sufficiently large for the accreted gas to avoid two conical-like openings along the two opposite polar directions.I suggest that the high-pressure zone that the accreted gas builds around the main sequence equatorial plane accelerates outflows along these polar openings.Most of the inflowing gas is deflected to the polar outflows,i.e.,two oppositely directed jets.The actual mass that the main sequence star accretes is only a small fraction,≈0.1,of the inflowing gas.However,the gravitational energy that this gas releases powers the inflow-outflow streaming of gas and adds energy to the common envelope ejection.This flow structure might take place during a grazing envelope evolution if it occurs,during the early CEE and possibly in some post-CEE cases.This study increases the parameter space for main sequence stars to launch jets.Such jets might shape some morphological features in planetary nebulae,add energy to mass removal in CEE and power some intermediate luminosity optical transients.展开更多
I further study the manner by which a pair of opposite jets shape the“keyhole”morphological structure of the core-collapse supernova(CCSN)SN 1997A,now the CCSN remnant(CCSNR)1987A.By doing so,I strengthen the claim ...I further study the manner by which a pair of opposite jets shape the“keyhole”morphological structure of the core-collapse supernova(CCSN)SN 1997A,now the CCSN remnant(CCSNR)1987A.By doing so,I strengthen the claim that the jittering-jet explosion mechanism accounts for most,likely all,CCSNe.The“keyhole”structure comprises a northern low-intensity zone closed with a bright rim on its front and an elongated low-intensity nozzle in the south.This rim-nozzle asymmetry is observed in some cooling flow clusters and planetary nebulae that are observed to be shaped by jets.I build a toy model that uses the planar jittering jets pattern,where consecutive pairs of jets tend to jitter in a common plane,implying that the accreted gas onto the newly born neutron star at the late explosion phase flows perpendicular to that plane.This allows for a long-lived jet-launching episode.This long-lasting jet-launching episode launches more mass into the jets that can inflate larger pairs of ears or bubbles,forming the main jets'axis of the CCSNR that is not necessarily related to a possible pre-collapse core rotation.I discuss the relation of the main jets'axis to the neutron star's natal kick velocity.展开更多
I identify a point-symmetric structure in recently published VLT/MUSE velocity maps of different elements in a plane along the line of sight at the center of the supernova remnant SNR 0540-69.3,and argue that jitterin...I identify a point-symmetric structure in recently published VLT/MUSE velocity maps of different elements in a plane along the line of sight at the center of the supernova remnant SNR 0540-69.3,and argue that jittering jets that exploded this core collapse supernova shaped this point-symmetric structure.The four pairs of two opposite clumps that compose this point symmetric structure suggest that two to four pairs of jittering jets shaped the inner ejecta in this plane.In addition,intensity images of several spectral lines reveal a faint strip(the main jet-axis)that is part of this plane of jittering jets and its similarity to morphological features in a few other SNRs and in some planetary nebulae further suggests shaping by jets.My interpretation implies that in addition to instabilities,jets also mix elements in the ejecta of core collapse supernovae.Based on the point-symmetric structure and under the assumption that jittering jets exploded this supernova,I estimate the component of the neutron star natal kick velocity on the plane of the sky to be■235 km s^(-1),and at an angle of■47°to the direction of the main jet-axis.I analyze this natal kick direction together with 12 other SNRs in the frame of the jittering jets explosion mechanism.展开更多
I use recent observations of circumstellar matter(CSM)around type Ia supernovae(SNe Ia)to estimate the fraction of SNe Ia that explode into a planetary nebula(PN)and to suggest a new delay time distribution from the c...I use recent observations of circumstellar matter(CSM)around type Ia supernovae(SNe Ia)to estimate the fraction of SNe Ia that explode into a planetary nebula(PN)and to suggest a new delay time distribution from the common envelope evolution(CEE)to the SN Ia explosion for SNe Ia that occur shortly after the CEE.Under the assumption that the CSM results from a CEE,I crudely estimate that about 50%of all SNe Ia are SNe Ia inside PNe(SNIPs),and that the explosions of most SNIPs occur within a CEE to explosion delay(CEED)time of less than about ten thousand years.I also estimate that the explosion rate of SNIPs,i.e.,the CEED time distribution,is roughly constant within this timescale of ten thousand years.The short CEED time suggests that a fraction of SNIPs come from the core-degenerate(CD)scenario where the merger of the core with the white dwarf takes place at the end of the CEE.I present my view that the majority of SNIPs come from the CD scenario.I list some further observations that might support or reject my claims,and describe the challenge to theoretical studies to find a process to explain a merger to explosion delay(MED)time of up to ten thousand years or so.A long MED will apply also to the double degenerate scenario.展开更多
I present a novel mechanism to boost magnetic field amplification of newly born neutron stars in core collapse supernovae.In this mechanism,that operates in the jittering jets explosion mechanism and comes on top of t...I present a novel mechanism to boost magnetic field amplification of newly born neutron stars in core collapse supernovae.In this mechanism,that operates in the jittering jets explosion mechanism and comes on top of the regular magnetic field amplification by turbulence,the accretion of stochastic angular momentum in core collapse supernovae forms a neutron star with strong initial magnetic fields but with a slow rotation.The varying angular momentum of the accreted gas,which is unique to the jittering jets explosion mechanism,exerts a varying azimuthal shear on the magnetic fields of the accreted mass near the surface of the neutron star.This,I argue,can form an amplifying effect which I term the stochastic omega(Sω) effect.In the common αω dynamo the rotation has constant direction and value,and hence supplies a constant azimuthal shear,while the convection has a stochastic behavior.In the Sω dynamo the stochastic angular momentum is different from turbulence in that it operates on a large scale,and it is different from a regular rotational shear in being stochastic.The basic assumption is that because of the varying direction of the angular momentum axis from one accretion episode to the next,the rotational flow of an accretion episode stretches the magnetic fields that were amplified in the previous episode.I estimate the amplification factor of the Sω dynamo alone to be ≈ 10.I speculate that the Sω effect accounts for a recent finding that many neutron stars are born with strong magnetic fields.展开更多
We conduct one-dimensional stellar evolution simulations of red supergiant(RSG)stars that mimic common envelope evolution(CEE)and find that the inner boundary of the envelope convective zone moves into the initial env...We conduct one-dimensional stellar evolution simulations of red supergiant(RSG)stars that mimic common envelope evolution(CEE)and find that the inner boundary of the envelope convective zone moves into the initial envelope radiative zone.The envelope convection practically disappears only when the RSG radius decreases by about an order of magnitude or more.The implication is that one cannot split the CEE into one stage during which the companion spirals-in inside the envelope convective zone and removes it,and a second slower phase when the companion orbits the initial envelope radiative zone and a stable mass transfer takes place.At best,this might take place when the orbital separation is about several solar radii.However,by that time other processes become important.We conclude that as of yet,the commonly used alpha-formalism that is based on energy considerations is the best phenomenological formalism.展开更多
I find that a≃0.1−1M⊙outflowing equatorial dusty disk(torus)that the binary system progenitor of an intermediate luminosity optical transient(ILOT)ejects several years to several months before and during the outburst...I find that a≃0.1−1M⊙outflowing equatorial dusty disk(torus)that the binary system progenitor of an intermediate luminosity optical transient(ILOT)ejects several years to several months before and during the outburst can reduce the total emission to an equatorial observer by two orders of magnitude and shifts the emission to wavelengths of mainlyλ≳10μm.This is termed a type II ILOT(ILOT II).To reach this conclusion,I use calculations of type II active galactic nuclei and apply them to the equatorial ejecta(disk/torus)of ILOTs II.This reduction in emission can last for tens of years after outburst.Most of the radiation escapes along the polar directions.The attenuation of the emission for wavelengths ofλ<5μm can be more than three orders of magnitude,and the emission atλ\lessim2μm is negligible.Jets that the binary system launches during the outburst can collide with polar CSM and emit radiation above the equatorial plane and dust in the polar outflow can reflect emission from the central source.Therefore,during the event itself the equatorial observer might detect an ILOT.I strengthen the previously suggested ILOT II scenario to the event N6946-BH1,where a red giant star disappeared in the visible.展开更多
We use recent X-ray observations of the intracluster medium （ICM） of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM prop- erties. We argue that the ICM ...We use recent X-ray observations of the intracluster medium （ICM） of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM prop- erties. We argue that the ICM of the cooling flow in the galaxy group NGC 5813 is more likely to be heated by mixing of post-shock gas from jets residing in hot bubbles with the ICM, than by shocks or turbulent- heating. Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow; in order to adequately heat the inner part of the ICM, they would overheat the outer regions by a large factor, leading to its ejection from the group. Heating by mixing, which was found to be much more efficient than turbulent-heating and shocks-heating, hence, rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.展开更多
We demonstrate by three-dimensional hydrodynamical simulations of energy deposition into the envelope of a red supergiant model the inflation of a Rayleigh–Taylor unstable envelope that forms a compact clumpy circums...We demonstrate by three-dimensional hydrodynamical simulations of energy deposition into the envelope of a red supergiant model the inflation of a Rayleigh–Taylor unstable envelope that forms a compact clumpy circumstellar material(CSM).Our simulations mimic vigorous core activity years to months before a core-collapse supernova(CCSN)explosion that deposits energy to the outer envelope.The fierce core nuclear activity in the pre-CCSN explosion phase might excite waves that propagate to the envelope.The wave energy is dissipated where envelope convection cannot carry the energy.We deposit this energy into a shell in the outer envelope with a power of L_(wave)=2.6×10^(6)L■or L_(wave)=5.2×10^(5)L■for 0.32 yr.The energy-deposition shell expands while its pressure is higher than its surroundings,but its density is lower.Therefore,this expansion is Rayleigh–Taylor unstable and develops instability fingers.Most of the inflated envelope does not reach the escape velocity in the year of simulation but forms a compact and clumpy CSM.The high density of the inflated envelope implies that if a companion is present in that zone,it will accrete mass at a very high rate and power a pre-explosion outburst.展开更多
I suggest the double-degenerate(DD)scenario with a merger-to-explosion delay(MED)time(the DD-MED scenario)of about 1-2 yr to explain the rare properties of the recently analyzed typeⅠa supernova(SN Ia)SN2020aeuh.The ...I suggest the double-degenerate(DD)scenario with a merger-to-explosion delay(MED)time(the DD-MED scenario)of about 1-2 yr to explain the rare properties of the recently analyzed typeⅠa supernova(SN Ia)SN2020aeuh.The rare properties are the SNⅠa ejecta interacting with a carbon-oxygen(CO)-rich circumstellar material(CSM)at approximately 50 days post-explosion.In this DD-MED scenario,two massive CO white dwarfs(WDs),with masses of M_(1)■1.1M_(☉)and M_(2)■M_(☉),merge to leave a rapidly rotating lonely WD of about the Chandrasekhar mass.The merger process ejects M_(CSM)■0.7M_(☉)to form a nonspherical CO-rich CSM.At the explosion,there is a lonely WD and a detached hydrogen-and helium-deficient CSM.Studies proposed the other lonely WD scenario,the core-degenerate(CD)scenario,to explain several specific SNe Ia and SN Ia remnants.SN 2020aeuh is the first particular SN Ia that is attributed to the DD-MED scenario.Besides being slightly brighter than typical SNe Ia and the CSM interaction,SN 2020aeuh is a normal SN Ia.Therefore,this study strengthens the claim of earlier studies,which are based on other arguments,like the properties of SN Ia remnants,that the lonely WD scenarios,i.e.,the DD-MED and CD scenarios,might account for most,if not all,normal SNe Ia.These earlier studies also argue that all SN Ia scenarios,whether lonely WD or not,might contribute to peculiar SNe Ia.展开更多
We propose that sub-Keplerian accretion belts around stars might launch jets. The sub-Keplerian inflow does not form a rotationally supported accretion disk, but it rather reaches the accreting object from a wide soli...We propose that sub-Keplerian accretion belts around stars might launch jets. The sub-Keplerian inflow does not form a rotationally supported accretion disk, but it rather reaches the accreting object from a wide solid angle. The basic ingredients of the flow are a turbulent region where the accretion belt interacts with the accreting object via a shear layer, and two avoidance regions on the poles where the accretion rate is very low. A dynamo that is developed in the shear layer amplifies magnetic fields to high values. It is likely that the amplified magnetic fields form polar outflows from the avoidance regions. Our speculative belt-launched jets model has implications on a rich variety of astrophysical objects, from the removal of common envelopes to the explosion of core collapse supernovae by jittering jets.展开更多
We suggest that in the rare case of an Intermediate-Luminosity Optical Transient（ILOT） event,evaporation of extra-solar Kuiper belt objects（Extra KBOs） at distances of dth to a few years, enough d≈500ust mig-10 0...We suggest that in the rare case of an Intermediate-Luminosity Optical Transient（ILOT） event,evaporation of extra-solar Kuiper belt objects（Extra KBOs） at distances of dth to a few years, enough d≈500ust mig-10 000 AU from the ILOT can be detected. If the ILOT lasts for 1 monht be ejected from the Extra KBOs for the infrared（IR） emission to be detected. Because of the large distance of the Extra KBOs,tens of years will pass before the ILOT wind disperses the dust. We suggest that after an ILOT outburst,there is a period of months to several years during which IR excess emission might hint at the existence of a Kuiper belt analog（Extra K-Belt）.展开更多
I present the effervescent zone model to account for the compact dense circumstellar material(CSM)around the progenitor of the core collapse supernova(CCSN)SN 2023ixf.The effervescent zone is composed of bound dense c...I present the effervescent zone model to account for the compact dense circumstellar material(CSM)around the progenitor of the core collapse supernova(CCSN)SN 2023ixf.The effervescent zone is composed of bound dense clumps that are lifted by stellar pulsation and envelope convection to distances of≈tens×au,and then fall back.The dense clumps provide most of the compact CSM mass and exist alongside the regular(escaping)wind.I crudely estimate that for a compact CSM within R_(CSM)≈30 au that contains M_(CSM)≈0.01 M_(⊙),the density of each clump is k_(b)≳3000 times the density of the regular wind at the same radius and that the total volume filling factor of the clumps is several percent.The clumps might cover only a small fraction of the CCSN photosphere in the first days post-explosion,accounting for the lack of strong narrow absorption lines.The long-lived effervescent zone is compatible with no evidence for outbursts in the years prior to the SN 2023ixf explosion and the large-amplitude pulsations of its progenitor,and it is an alternative to the CSM scenario of several-years-long high mass loss rate wind.展开更多
基金A grant from the Pazy Foundation supported this research
文摘We identify an S-shaped main-jet axis in the Vela core-collapse supernova remnant(CCSNR)that we attribute to a pair of precessing jets,one of the tens of pairs of jets that exploded the progenitor of Vela according to the jittering jets explosion mechanism(JJEM).A main-jet axis is a symmetry axis across the CCSNR and through the center.We identify the S-shaped main-jet axis by the high abundance of ejecta elements,oxygen,neon,and magnesium.We bring the number of identified pairs of clumps and ears in Vela to seven,two pairs shaped by the pair of precessing jets that formed the main-jet axis.The pairs and the main-jet axis form the point-symmetric wind-rose structure of Vela.The other five pairs of clumps/ears do not have signatures near the center,only on two opposite sides of the CCSNR.We discuss different possible jet-less shaping mechanisms to form such a point-symmetric morphology and dismiss these processes because they cannot explain the point-symmetric morphology of Vela,the S-shaped high ejecta abundance pattern,and the enormous energy required to shape the S-shaped structure.Our findings strongly support the JJEM and further severely challenge the neutrino-driven explosion mechanism.
基金A grant from the Pazy Foundation supported this research.
文摘With a one-dimensional stellar evolution model,we find that massive main sequence stars can accrete mass at very high mass accretion rates without expanding much if they lose a significant fraction of this mass from their outer layers simultaneously with mass accretion.We assume the accretion process is via an accretion disk that launches powerful jets from its inner zones.These jets remove the outer high-entropy layers of the mass-accreting star.This process operates in a negative feedback cycle,as the jets remove more envelope mass when the star expands.With the one-dimensional model,we mimic the mass removal by jets by alternating mass addition and mass removal phases.For the simulated models of 30M☉and 60M☉,the star does not expand much if we remove more than about half of the added mass in not-too-short episodes.This holds even if we deposit the energy the jets do not carry into the envelope.As the star does not expand much,its gravitational potential well stays deep,and the jets are energetic.These results are relevant to bright transient events of binary systems powered by accretion and the launching of jets,e.g.,intermediate luminosity optical transients,including some luminous red novae,the grazing envelope evolution,and the 1837–1856 Great Eruption of Eta Carinae.
文摘We use a simple dynamical scheme to simulate the ejecta of type Ⅰa supernova(SN Ia) scenarios with two exploding white dwarfs(WDs) and find that the velocity distribution of the ejecta has difficulties accounting for bimodal emission line profiles with a large separation between the two emission peaks.The essence of the dynamical code is in including the fact that the ejecta does not leave the system instantaneously.We find that the final separation velocity between the centers of masses of the two WDs' ejecta is ≃80% of the pre-explosion WDs' orbital velocity,i.e.,we find separation velocities of 4200-5400 km s^(-1) for two WDs of masses M_(1)=M_(2)=0.94 M⊙.The lower separation velocities we find challenge scenarios with two exploding WDs to explain bimodal emission line profiles with observed velocity separations of up to ≃7000 km s^(-1).Only the mass in the ejecta of one WD with an explosion velocity lower than the separation velocity contributes to one peak of the bimodal profile;this is the inner ejecta.We find the inner ejecta to be only≲15% of the ejecta mass in energetic explosions.Less energetic explosions yield higher inner mass but lower separation velocities.We encourage searching for alternative explanations of bimodal line profiles.
基金supported by the National Key Research and Development Program of China(Grant No.2024YFA1410300)the National Natural Science Foundation of China(Grant No.12304217)+1 种基金the Natural Science Foundation of Hunan Province(Grant No.2025JJ60002)the Fundamental Research Funds for the Central Universities of China(Grant No.531119200247)。
文摘Moirésuperlattices hosting flat bands and correlated states have become a central focus in condensed matter research.Using first-principles calculations,we investigate three-dimensional flat bands in alternating twisted NbSe_(2)moirébulk structures,which exhibit stronger interlayer interactions than twisted bilayer configurations.Our results show that moirébulks undergo spontaneous large-scale structural relaxation,leading to the formation of remarkably flat energy bands at twist angles≤7.31°.The k_(z)-dependent dispersion of these flat bands across different moirébulks highlights their intrinsic three-dimensional character.Moreover,the presence of out-of-plane mirror symmetry in these moirébulk structures indicates potential interlayer triplet superconducting pairing mechanisms,distinct from those in twisted bilayer systems.This work opens new avenues for exploring three-dimensional flat bands in other moirébulk systems.
基金supported by a grant from the Israel Science Foundation (769/20)。
文摘I review studies of core collapse supernovae(CCSNe) and similar transient events that attribute major roles to jets in powering most CCSNe and in shaping their ejecta. I start with reviewing the jittering jets explosion mechanism that I take to power most CCSN explosions. Neutrino heating does play a role in boosting the jets. I compare the morphologies of some CCSN remnants to planetary nebulae to conclude that jets and instabilities are behind the shaping of their ejecta. I then discuss CCSNe that are descendants of rapidly rotating collapsing cores that result in fixed-axis jets(with small jittering) that shape bipolar ejecta. A large fraction of the bipolar CCSNe are superluminous supernovae(SLSNe). I conclude that modeling of SLSN light curves and bumps in the light curves must include jets, even when considering energetic magnetars and/or ejecta interaction with the circumstellar matter(CSM). I connect the properties of bipolar CCSNe to common envelope jets supernovae(CEJSNe) where an old neutron star or a black hole spirals-in inside the envelope and then inside the core of a red supergiant. I discuss how jets can shape the pre-explosion CSM, as in Supernova 1987A, and can power pre-explosion outbursts(precursors)in binary system progenitors of CCSNe and CEJSNe. Binary interaction also facilitates the launching of postexplosion jets.
基金support provided by the National Science Foundation through grant AST1109394
文摘We follow the premise that most intermediate luminosity optical transients （ILOTs） are powered by rapid mass accretion onto a main sequence star, and study the effects of jets launched by an accretion disk. The disk is formed due to large specific angular momentum of the accreted mass. The two opposite jets might expel some of the mass from the reservoir of gas that feeds the disk, and therefore reduce and shorten the mass accretion process. We argue that by this process ILOTs limit their luminosity and might even shut themselves off in this negative jet feedback mechanism （JFM）. The group of ILOTs is a new member of a large family of astrophysical objects whose activity is regulated by the operation of the JFM.
基金a grant from the Israel Science Foundation(769/20).
文摘I build a toy model in the frame of the jittering jets explosion mechanism(JJEM)of core collapse supernovae that incorporates both the stochastically varying angular momentum component of the material that the newly born neutron star(NS)accretes and the constant angular momentum component,and show that the JJEM can account for the≃2.5–5M⊙mass gap between NSs and black holes(BHs).The random component of the angular momentum results from pre-collapse core convection fluctuations that are amplified by post-collapse instabilities.The fixed angular momentum component results from pre-collapse core rotation.For slowly rotating pre-collapse cores the stochastic angular momentum fluctuations form intermittent accretion disks(or belts)around the NS with varying angular momentum axes in all directions.The intermittent accretion disk/belt launches jets in all directions that expel the core material in all directions early on,hence leaving an NS remnant.Rapidly rotating pre-collapse cores form an accretion disk with angular momentum axis that is about the same as the pre-collapse core rotation.The NS launches jets along this axis and hence the jets avoid the equatorial plane region.Inflowing core material continues to feed the central object from the equatorial plane increasing the NS mass to form a BH.The narrow transition from slow to rapid pre-collapse core rotation,i.e.,from an efficient to inefficient jet feedback mechanism,accounts for the sparsely populated mass gap.
基金supported by a grant from the Israel Science Foundation (769/20)by the Pazy Research Foundation。
文摘I consider a flow structure by which main sequence companions that enter a common envelope evolution(CEE)with giant stars might launch jets even when the accreted gas has a sub-Keplerian specific angular momentum.I first show that after a main sequence star enters the envelope of a giant star the specific angular momentum of the accreted gas is sub-Keplerian but still sufficiently large for the accreted gas to avoid two conical-like openings along the two opposite polar directions.I suggest that the high-pressure zone that the accreted gas builds around the main sequence equatorial plane accelerates outflows along these polar openings.Most of the inflowing gas is deflected to the polar outflows,i.e.,two oppositely directed jets.The actual mass that the main sequence star accretes is only a small fraction,≈0.1,of the inflowing gas.However,the gravitational energy that this gas releases powers the inflow-outflow streaming of gas and adds energy to the common envelope ejection.This flow structure might take place during a grazing envelope evolution if it occurs,during the early CEE and possibly in some post-CEE cases.This study increases the parameter space for main sequence stars to launch jets.Such jets might shape some morphological features in planetary nebulae,add energy to mass removal in CEE and power some intermediate luminosity optical transients.
文摘I further study the manner by which a pair of opposite jets shape the“keyhole”morphological structure of the core-collapse supernova(CCSN)SN 1997A,now the CCSN remnant(CCSNR)1987A.By doing so,I strengthen the claim that the jittering-jet explosion mechanism accounts for most,likely all,CCSNe.The“keyhole”structure comprises a northern low-intensity zone closed with a bright rim on its front and an elongated low-intensity nozzle in the south.This rim-nozzle asymmetry is observed in some cooling flow clusters and planetary nebulae that are observed to be shaped by jets.I build a toy model that uses the planar jittering jets pattern,where consecutive pairs of jets tend to jitter in a common plane,implying that the accreted gas onto the newly born neutron star at the late explosion phase flows perpendicular to that plane.This allows for a long-lived jet-launching episode.This long-lasting jet-launching episode launches more mass into the jets that can inflate larger pairs of ears or bubbles,forming the main jets'axis of the CCSNR that is not necessarily related to a possible pre-collapse core rotation.I discuss the relation of the main jets'axis to the neutron star's natal kick velocity.
基金supported by a grant from the Israel Science Foundation(769/20)。
文摘I identify a point-symmetric structure in recently published VLT/MUSE velocity maps of different elements in a plane along the line of sight at the center of the supernova remnant SNR 0540-69.3,and argue that jittering jets that exploded this core collapse supernova shaped this point-symmetric structure.The four pairs of two opposite clumps that compose this point symmetric structure suggest that two to four pairs of jittering jets shaped the inner ejecta in this plane.In addition,intensity images of several spectral lines reveal a faint strip(the main jet-axis)that is part of this plane of jittering jets and its similarity to morphological features in a few other SNRs and in some planetary nebulae further suggests shaping by jets.My interpretation implies that in addition to instabilities,jets also mix elements in the ejecta of core collapse supernovae.Based on the point-symmetric structure and under the assumption that jittering jets exploded this supernova,I estimate the component of the neutron star natal kick velocity on the plane of the sky to be■235 km s^(-1),and at an angle of■47°to the direction of the main jet-axis.I analyze this natal kick direction together with 12 other SNRs in the frame of the jittering jets explosion mechanism.
基金supported by a grant from the Israel Science Foundation(769/20)。
文摘I use recent observations of circumstellar matter(CSM)around type Ia supernovae(SNe Ia)to estimate the fraction of SNe Ia that explode into a planetary nebula(PN)and to suggest a new delay time distribution from the common envelope evolution(CEE)to the SN Ia explosion for SNe Ia that occur shortly after the CEE.Under the assumption that the CSM results from a CEE,I crudely estimate that about 50%of all SNe Ia are SNe Ia inside PNe(SNIPs),and that the explosions of most SNIPs occur within a CEE to explosion delay(CEED)time of less than about ten thousand years.I also estimate that the explosion rate of SNIPs,i.e.,the CEED time distribution,is roughly constant within this timescale of ten thousand years.The short CEED time suggests that a fraction of SNIPs come from the core-degenerate(CD)scenario where the merger of the core with the white dwarf takes place at the end of the CEE.I present my view that the majority of SNIPs come from the CD scenario.I list some further observations that might support or reject my claims,and describe the challenge to theoretical studies to find a process to explain a merger to explosion delay(MED)time of up to ten thousand years or so.A long MED will apply also to the double degenerate scenario.
基金supported by a grant from the Israel Science Foundation
文摘I present a novel mechanism to boost magnetic field amplification of newly born neutron stars in core collapse supernovae.In this mechanism,that operates in the jittering jets explosion mechanism and comes on top of the regular magnetic field amplification by turbulence,the accretion of stochastic angular momentum in core collapse supernovae forms a neutron star with strong initial magnetic fields but with a slow rotation.The varying angular momentum of the accreted gas,which is unique to the jittering jets explosion mechanism,exerts a varying azimuthal shear on the magnetic fields of the accreted mass near the surface of the neutron star.This,I argue,can form an amplifying effect which I term the stochastic omega(Sω) effect.In the common αω dynamo the rotation has constant direction and value,and hence supplies a constant azimuthal shear,while the convection has a stochastic behavior.In the Sω dynamo the stochastic angular momentum is different from turbulence in that it operates on a large scale,and it is different from a regular rotational shear in being stochastic.The basic assumption is that because of the varying direction of the angular momentum axis from one accretion episode to the next,the rotational flow of an accretion episode stretches the magnetic fields that were amplified in the previous episode.I estimate the amplification factor of the Sω dynamo alone to be ≈ 10.I speculate that the Sω effect accounts for a recent finding that many neutron stars are born with strong magnetic fields.
基金supported by a grant from the Israel Science Foundation(769/20)。
文摘We conduct one-dimensional stellar evolution simulations of red supergiant(RSG)stars that mimic common envelope evolution(CEE)and find that the inner boundary of the envelope convective zone moves into the initial envelope radiative zone.The envelope convection practically disappears only when the RSG radius decreases by about an order of magnitude or more.The implication is that one cannot split the CEE into one stage during which the companion spirals-in inside the envelope convective zone and removes it,and a second slower phase when the companion orbits the initial envelope radiative zone and a stable mass transfer takes place.At best,this might take place when the orbital separation is about several solar radii.However,by that time other processes become important.We conclude that as of yet,the commonly used alpha-formalism that is based on energy considerations is the best phenomenological formalism.
基金This research was supported by a grant from the Israel Science Foundation(420/16 and 769/20)a grant from the Asher Space Research Fund at the Technion.
文摘I find that a≃0.1−1M⊙outflowing equatorial dusty disk(torus)that the binary system progenitor of an intermediate luminosity optical transient(ILOT)ejects several years to several months before and during the outburst can reduce the total emission to an equatorial observer by two orders of magnitude and shifts the emission to wavelengths of mainlyλ≳10μm.This is termed a type II ILOT(ILOT II).To reach this conclusion,I use calculations of type II active galactic nuclei and apply them to the equatorial ejecta(disk/torus)of ILOTs II.This reduction in emission can last for tens of years after outburst.Most of the radiation escapes along the polar directions.The attenuation of the emission for wavelengths ofλ<5μm can be more than three orders of magnitude,and the emission atλ\lessim2μm is negligible.Jets that the binary system launches during the outburst can collide with polar CSM and emit radiation above the equatorial plane and dust in the polar outflow can reflect emission from the central source.Therefore,during the event itself the equatorial observer might detect an ILOT.I strengthen the previously suggested ILOT II scenario to the event N6946-BH1,where a red giant star disappeared in the visible.
文摘We use recent X-ray observations of the intracluster medium （ICM） of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM prop- erties. We argue that the ICM of the cooling flow in the galaxy group NGC 5813 is more likely to be heated by mixing of post-shock gas from jets residing in hot bubbles with the ICM, than by shocks or turbulent- heating. Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow; in order to adequately heat the inner part of the ICM, they would overheat the outer regions by a large factor, leading to its ejection from the group. Heating by mixing, which was found to be much more efficient than turbulent-heating and shocks-heating, hence, rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.
基金A grant from the Pazy Foundation supported this research。
文摘We demonstrate by three-dimensional hydrodynamical simulations of energy deposition into the envelope of a red supergiant model the inflation of a Rayleigh–Taylor unstable envelope that forms a compact clumpy circumstellar material(CSM).Our simulations mimic vigorous core activity years to months before a core-collapse supernova(CCSN)explosion that deposits energy to the outer envelope.The fierce core nuclear activity in the pre-CCSN explosion phase might excite waves that propagate to the envelope.The wave energy is dissipated where envelope convection cannot carry the energy.We deposit this energy into a shell in the outer envelope with a power of L_(wave)=2.6×10^(6)L■or L_(wave)=5.2×10^(5)L■for 0.32 yr.The energy-deposition shell expands while its pressure is higher than its surroundings,but its density is lower.Therefore,this expansion is Rayleigh–Taylor unstable and develops instability fingers.Most of the inflated envelope does not reach the escape velocity in the year of simulation but forms a compact and clumpy CSM.The high density of the inflated envelope implies that if a companion is present in that zone,it will accrete mass at a very high rate and power a pre-explosion outburst.
文摘I suggest the double-degenerate(DD)scenario with a merger-to-explosion delay(MED)time(the DD-MED scenario)of about 1-2 yr to explain the rare properties of the recently analyzed typeⅠa supernova(SN Ia)SN2020aeuh.The rare properties are the SNⅠa ejecta interacting with a carbon-oxygen(CO)-rich circumstellar material(CSM)at approximately 50 days post-explosion.In this DD-MED scenario,two massive CO white dwarfs(WDs),with masses of M_(1)■1.1M_(☉)and M_(2)■M_(☉),merge to leave a rapidly rotating lonely WD of about the Chandrasekhar mass.The merger process ejects M_(CSM)■0.7M_(☉)to form a nonspherical CO-rich CSM.At the explosion,there is a lonely WD and a detached hydrogen-and helium-deficient CSM.Studies proposed the other lonely WD scenario,the core-degenerate(CD)scenario,to explain several specific SNe Ia and SN Ia remnants.SN 2020aeuh is the first particular SN Ia that is attributed to the DD-MED scenario.Besides being slightly brighter than typical SNe Ia and the CSM interaction,SN 2020aeuh is a normal SN Ia.Therefore,this study strengthens the claim of earlier studies,which are based on other arguments,like the properties of SN Ia remnants,that the lonely WD scenarios,i.e.,the DD-MED and CD scenarios,might account for most,if not all,normal SNe Ia.These earlier studies also argue that all SN Ia scenarios,whether lonely WD or not,might contribute to peculiar SNe Ia.
基金supported by the Asher Fund for Space Research at the Technionthe E. and J. Bishop Research Fund at the Technion
文摘We propose that sub-Keplerian accretion belts around stars might launch jets. The sub-Keplerian inflow does not form a rotationally supported accretion disk, but it rather reaches the accreting object from a wide solid angle. The basic ingredients of the flow are a turbulent region where the accretion belt interacts with the accreting object via a shear layer, and two avoidance regions on the poles where the accretion rate is very low. A dynamo that is developed in the shear layer amplifies magnetic fields to high values. It is likely that the amplified magnetic fields form polar outflows from the avoidance regions. Our speculative belt-launched jets model has implications on a rich variety of astrophysical objects, from the removal of common envelopes to the explosion of core collapse supernovae by jittering jets.
基金supported by the Asher Fund for Space Research at the Technionthe E.and J.Bishop Research Fund at the Technion
文摘We suggest that in the rare case of an Intermediate-Luminosity Optical Transient（ILOT） event,evaporation of extra-solar Kuiper belt objects（Extra KBOs） at distances of dth to a few years, enough d≈500ust mig-10 000 AU from the ILOT can be detected. If the ILOT lasts for 1 monht be ejected from the Extra KBOs for the infrared（IR） emission to be detected. Because of the large distance of the Extra KBOs,tens of years will pass before the ILOT wind disperses the dust. We suggest that after an ILOT outburst,there is a period of months to several years during which IR excess emission might hint at the existence of a Kuiper belt analog（Extra K-Belt）.
基金supported by a grant from the Israel Science Foundation(769/20)。
文摘I present the effervescent zone model to account for the compact dense circumstellar material(CSM)around the progenitor of the core collapse supernova(CCSN)SN 2023ixf.The effervescent zone is composed of bound dense clumps that are lifted by stellar pulsation and envelope convection to distances of≈tens×au,and then fall back.The dense clumps provide most of the compact CSM mass and exist alongside the regular(escaping)wind.I crudely estimate that for a compact CSM within R_(CSM)≈30 au that contains M_(CSM)≈0.01 M_(⊙),the density of each clump is k_(b)≳3000 times the density of the regular wind at the same radius and that the total volume filling factor of the clumps is several percent.The clumps might cover only a small fraction of the CCSN photosphere in the first days post-explosion,accounting for the lack of strong narrow absorption lines.The long-lived effervescent zone is compatible with no evidence for outbursts in the years prior to the SN 2023ixf explosion and the large-amplitude pulsations of its progenitor,and it is an alternative to the CSM scenario of several-years-long high mass loss rate wind.
