Coalescing Neutron Stars A Solution to the R-Process Problem
插上科学的翅膀在火星上居住作文
插上科学的翅膀在火星上居住作文英文回答：In the vast expanse of the cosmos, where celestial wonders beckon, the allure of extraterrestrial life and the prospect of establishing human colonies beyond Earth have captivated the imaginations of scientists, explorers, and dreamers alike. Among these celestial destinations, Mars, with its enigmatic terrain and potential for habitability, has emerged as a prime candidate for future human expansion. To achieve this audacious goal, we must harness the powerof science, innovation, and unwavering determination.To establish a thriving Martian habitat, we must first overcome the challenges posed by the planet's harsh environment. The Martian atmosphere is thin and devoid of oxygen, exposing any potential inhabitants to harmful radiation. To mitigate these hazards, we will need to develop innovative shielding and life support systems that can provide a breathable atmosphere and protect againstharmful cosmic rays.Water, an essential ingredient for life as we know it, is scarce on Mars. However, evidence suggests the presence of significant ice reserves beneath the Martian surface. By employing advanced drilling and extraction technologies, we can tap into these subterranean water sources and provide a sustainable supply for our Martian colonists.Producing food in the Martian environment will be another significant hurdle. The planet's thin atmosphere and limited sunlight pose challenges for conventional agriculture. However, advancements in hydroponics, aeroponics, and controlled environment agriculture offer promising solutions. By harnessing artificial lighting and optimizing nutrient delivery, we can establish sustainable food production systems that can nourish a growing Martian population.Energy is vital for any human settlement. Mars receives ample sunlight, making solar energy a viable source. By deploying large-scale solar arrays, we can harvest thesun's rays and convert them into electricity. Nuclear power, with its compact and efficient nature, may also play a role in providing a reliable energy supply.Transportation is another critical aspect of Martian colonization. With vast distances to cover and a varied Martian landscape, we will need versatile and durable vehicles. Rovers, landers, and even flying vehicles will be essential for exploration, resource extraction, and the construction of new outposts.Beyond the physical challenges, we must also consider the human and social aspects of Martian colonization. Extended isolation, exposure to radiation, and the psychological strain of living in an unfamiliar environment raise significant concerns. To address these issues, wemust invest in psychological support, foster a sense of community, and develop protocols to ensure the physical and mental well-being of our Martian pioneers.International collaboration will be essential for the success of any Martian colonization endeavor. Sharingresources, expertise, and scientific knowledge will be crucial for overcoming the formidable challenges posed by the Martian environment. By pooling our collective knowledge and capabilities, we can accelerate the pace of progress and minimize the risks associated with this unprecedented undertaking.The establishment of a permanent human presence on Mars represents a transformative leap in our species' history.It offers the potential for scientific discovery, economic growth, and the expansion of human knowledge beyond the confines of our home planet. By embracing the scientific method, fostering innovation, and collaborating on a global scale, we can turn the dream of Martian colonization into a tangible reality, opening up new frontiers for human exploration and unlocking the secrets of the cosmos.中文回答：在浩瀚的宇宙中，那里有星际奇观招引着，在火星上居住的外星生命和建立人类新家园的前景，已经吸引了很多科学家、探险者和梦想家们的想象力。
航天科学知识英语作文
航天科学知识英语作文Title: Exploring the Frontiers of Space Science。
In recent decades, humanity has witnessed remarkable advancements in the field of space science. From pioneering missions to distant planets to the study of cosmic phenomena, our understanding of the universe has expanded exponentially. In this essay, we delve into key developments in space science and their significance.One of the most notable achievements in space exploration is the successful landing and exploration of Mars by various space agencies, notably NASA's Mars rovers. These robotic vehicles, equipped with advanced instruments, have provided invaluable data about the Martian surface, atmosphere, and geological history. Through their discoveries, scientists have gained insights into the possibility of past life on Mars and the planet's potential habitability.Moreover, the exploration of our solar system extends beyond Mars. Missions like the Cassini-Huygens mission to Saturn and its moons have revealed the wonders of the ringed planet and its diverse satellites. Cassini's observations have deepened our understanding of Saturn's atmosphere, magnetosphere, and intriguing moon Titan, where hydrocarbon lakes and a thick atmosphere resembling Earth's early conditions have been discovered.Beyond our solar system, the search for exoplanets –planets orbiting distant stars – has captured the imagination of scientists and the public alike. Thanks to missions like the Kepler Space Telescope, thousands of exoplanets have been discovered, revolutionizing our understanding of planetary systems. These discoveries raise intriguing questions about the prevalence of Earth-like planets and the potential for extraterrestrial life.Furthermore, space science encompasses the study of cosmic phenomena such as black holes, neutron stars, and gravitational waves. Breakthroughs in observational techniques, including the development of powerfultelescopes and detectors, have allowed scientists to probe the most extreme environments in the universe. The detection of gravitational waves – ripples in spacetime caused by cataclysmic events like black hole mergers – has opened a new window onto the cosmos, providing a direct means of studying phenomena previously inaccessible to traditional telescopes.In addition to exploration and observation, space science plays a crucial role in technological innovation and societal benefits. Satellites orbiting Earth enable global communication, weather forecasting, navigation, and monitoring of environmental changes. Space-based technologies have also led to advances in medicine, agriculture, and disaster management, improving the quality of life for people around the world.Looking ahead, the future of space science holds immense promise. Proposed missions include the exploration of icy moons like Europa and Enceladus, where subsurface oceans may harbor conditions conducive to life. Plans for crewed missions to Mars and beyond are also underdevelopment, reflecting humanity's enduring desire to explore and expand our presence in the cosmos.In conclusion, space science stands at the forefront of human exploration and discovery. Through missions todistant planets, the search for exoplanets, and the study of cosmic phenomena, we continue to unravel the mysteries of the universe. Moreover, space science drives technological innovation and benefits society in countless ways. As we look to the future, the quest to understand our place in the cosmos remains a driving force for scientific inquiry and exploration.。
Accretion Models for Young Neutron Stars
One basic motivation for accretion/propeller models is that the narrow range of rotation periods, common to AXP and SGR, and also to the Dim Thermal Neutron Stars, has a natural explanation in terms of rotational equilibrium between neutron star and disk. Transitions between accreting and propeller states (transients- Cui et al 1998, Campana et al 1998), and between spinup and spindown (eg Lovelace, Romanova & Bisnovatyi-Kogan 1999) occur near the equilibrium regime. As the rotational equilibrium is approached asymptotically, systems would tend to spend a long part of their lives near equilibrium and hence tend to be observed at their equilibrium periods. AXPs are spinning down while accreting because the fallback disk is evolving, with the inner disk radius receding from the neutron star, and the equlibrium period, which the star tracks, increasing as the mass inflow rate decreases (Chatterjee, Hernquist & Narayan 2000). The narrow range of observed periods correspond to equilibrium periods with dipole surface magnetic fields in the 1012 G range and a not very restrictive range of mass inflow rates (Alpar 2001): AXP, SGR and DTN periods, with 1012 G fields, imply an M˙ (t) range restricted to two orders of magnitude. There is a selection based on M˙ (t). According to the suggested classification AXPs and SGRs are the sources that get to equilibrium accretion before the disk depletes. DTNs are also close to equilibrium
Understanding the Universe, 2nd, Part II
he was voted the “Best Professor” on campus in student polls. Also, in 2002, he received the Distinguished Research Mentoring of Undergraduates Award, given by UC Berkeley. Dr. Filippenko has delivered hundreds of public lectures on astronomy and has played a prominent role in science newscasts and television documentaries, such as “Mysteries of Deep Space.” “Stephen Hawking's Universe,” and Nova's “Runaway Universe.” With Jay M. Pasachoff, Dr. Filippenko coauthored an introductory astronomy textbook, The Cosmos: Astronomy in the New Millennium (2001; 2004, 2nd ed.; 2007, 3rd ed.), which in 2001, won the Texty Excellence Award of the Text and Academic Authors Association for the best new textbook in the physical sciences. In 1998, Dr. Filippenko produced a 40-lecture introductory astronomy video course with The Teaching Company, and in 2003, he recorded a 16-lecture update. Dr. Filippenko was the recipient of the 2004 Carl Sagan Prize for Science Popularization from the Trustees of Wonderfest, the San Francisco Bay Area Festival of Science. The Carnegie Foundation for the Advancement of Teaching and the Council for Advancement and Support of Education honored him as the “Outstanding Doctoral and Research Universities Professor of the Year” in 2006.
2023届高考英语最新热点时文阅读：韦伯望远镜捕捉到猎户座大星云
James Webb Space Telescope spots babystars韦伯望远镜捕捉到猎户座大星云The Orion Nebula is one of the brightest star-forming regions visible in the night sky even with the naked eye. Newborn stars still wrapped in cocoons of dust and gas are revealed in a new image of the famous Orion Nebula captured by the James Webb Space Telescope. The image, taken on Sept. 11 with the telescope’s NIRCam instrument reveals unprecedented details of the Orion Nebula, a known star-forming region.猎户座星云是夜空中即使用肉眼也能看到的最明亮的恒星形成区域之一。
美国国家航天局（NASA）的詹姆斯·韦伯太空望远镜拍摄的著名猎户座星云的新图像显示，新生的恒星仍然包裹在尘埃和气体茧中。
这幅由韦伯望远镜的NIRCam成像仪于当地时间9月11日拍摄的图像揭示了猎户座星云前所未有的细节，这是一个已知的恒星形成区域。
Fine structures in the dense dust and gas clouds that form the nebula come to the fore in the image with much greater clarity than in a previous image captured by Webb’s predecessor, the Hubble Space Telescope. Thenebula, which can be found in the night sky in the constellation Orion just south of the archer’s belt, features a wall of dense gas and dust known as the Orion Bar.形成星云的致密尘埃云和气体云中的精细结构在这张照片中凸显出来，比韦伯的前身哈勃望远镜此前捕捉到的照片清晰得多。
Possible Signatures of Quark-Hadron Phase Transitions inside Neutron Stars
a r X iv :as tr o-ph/16169v19J un21POSSIBLE SIGNATURES OF QUARK-HADRON PHASE TRANSITIONS INSIDE NEUTRON STARS FENG MA McDonald Observatory,the University of Texas at Austin,Austin,TX 78712-1083,USA Email:feng@ The spin-down power of an isolated neutron star can drive its central density in-crease and overall structural changes,and trigger a quark–hadron phase transition.A series of observational signatures may be seen as a result of the phase transi-tion,including pulsar spin-down and glitch behaviors,Soft Gamma Repeaters or Gamma-Ray Bursts.1Introduction The sky has long been a successful test ground and discovery site for fun-damental physics.Examples include the discovery of Helium from solar spectrum in 1868,evidence for gravity waves from binary pulsars 1in 1978,and more recently in 1985,the discovery of Bucky Balls (C 60),though not directly in the sky,through experiments designed to simulate environments near stars in favor of forming long chain carbon molecules 2.Quark–hadron phase transitions are being pursued in accelerators in the high temperature regime.Meanwhile,the densities inside neutron stars may be high enough to allow the existence of deconfined quark matter.1.1A Neutron Star with a Quark Core The structure of a neutron star with a quark core can be solved using standard equations of stellar structure 3together with the equations of state (EOSs)of quark matter and normal neutron matter.The EOS of quark matter is much softer than that of neutron matter because of QCD asymptotic freedom.A neutron star containing a quark core is thus more compact than a normalneutron star.Consequently,the star has a larger maximum spin frequency.However,submillisecond pulsars have not been discovered and hence quark stars have not been identified this way.1.2Rotating Relativistic StarsTo solve the structure of a rotating relativistic star,Hartle developed 4,5a perturbation solution based on the Schwarzschild metric of a static,spherically wsllwi:submitted to World Scientific on February 1,20081symmetric object.Rotation distorts the star away from spherical symmetry, and its perturbed metric has the formds2=−e2νdt2+e2λdr2+e2µdθ2+e2φ(dφ−ωdt)2+O(Ω3).(1) In this line element,ωis the angular frequency of the star’sfluid in a local inertial frame and depends on the radial coordinate r.It is related toΩ, the rotational frequency seen by a distant observer.In this way,the mass–central density relation can be solved for rotating compact stars5,6,7.We note that,the mass“increase”,which is a main result in these works,represents the mass difference between two stars at different angular velocities with the same central density.Hence,these theoretical results are about star families relating to observations through pulsar statistics,and are difficult to be tested. 2Predictions on Quark-Core Neutron Star Spin-Down Behavior2.1Another Way to Apply Hartle’s Perturbation MethodInstead of deriving mass–central density relations for a set of neutron stars, we have suggested to trace the evolution of an isolated neutron star during its spin-down process8.Associated with the central density increase,neu-tron matter is continuously converted to quark matter.The overall structure and spin-down behaviors of the star are modified.In Hartle’s perturbation method,the central density isfixed as an input parameter,then stellar masses are solved as a function of angular frequency.In principle,we can derive a set of equations parallel to those of Hartle,with afixed mass as an input and central density as a perturbation,and solve the central density and stellar structure as a function of angular velocities.In practice,it is more convenient to apply Hartle’s method in a different way to solve the change of central density of an isolated star.An isolated neutron star has approximately constant gravitational mass during its spin–down process.The binding energy of a typical neutron star W∼1053erg,and the ratio of rotational energy to gravitational energy is less than0.1for the most rapidly rotating neutron star7.Since M⊙∼1054erg, the rotational energy is only1%of the stellar mass.In calculating the stellar configurations at different angular velocities,we needfirst to plot the mass–central density relation at different angular velocities using Hartle’s method as in previous work5,6,7.Under our approximation,we cross these curves with a line of constant mass,and the corresponding central densities are those of a rotating star at different angular velocities.wsllwi:submitted to World Scientific on February1,200822.2Pulsar GlitchesThe quarks inside the star are charged particles and are coupled with the solid crust through magneticfields.They rotate at a different velocity from superfluid neutrons.During the spin–down process,the central density and the quark core grow and so does the fractional moment of inertia of quark matter as compared to the whole star(I q/I).In a simple starquake model, the post–glitch behavior of a pulsar can be described approximately as3,Ω(t)=Ω0(t)+∆Ω0[Qe−t/τ+1−Q],(2)where Q is the healing parameter of the pulsar.Q=−τ∆˙Ω(t=0)/∆Ω,and τ=−∆Ω/∆¨Ω(t=0).It has been shown that Q∝I n/I(ref.3),where I=I n+ I c is the total moment of inertia of the star,I n is the moment of inertia carried by neutral particles,and I c is that of charged particles.Hence,a decreasing Q over a long term may indicate continuous conversion from neutron matter to quark matter inside the pulsar.2.3Spin-Down HistoryThe pulsar spin-down can be described as3˙Ω=−kΩn,(3) and the braking index n increases as the moment of inertia decreases,∆n/n∝−∆I/I.(4)As a result,|˙Ω|is larger because the quark-core neutron star has a smaller I and thus is easier to brake.At the same time,the star tends to“spin–up”during the early stages of the phase transitions causing a higherΩthan in the normal neutron star case.Consequently,the“characteristic age”τ=Ω/2|˙Ω|=k−1Ω1−n(5)may underestimate the true age of the neutron star with a quark core9,while for a normal neutron starτis an upper limit.3Onset of the Phase Transition:Catastrophic or Continuous? 3.1Event RateIn the previous section we considered the neutron star with a developed quark core in it.What if the central density of a normal neutron star happens to wsllwi:submitted to World Scientific on February1,20083increase from sub-critical density to critical density?Apparently the chance for this to happen is low,and we can estimate the event rate as10R≃10−5 P i10−2 yr−1galaxy−1,(6) where R NS is the average neutron star birth rate in units of per year per galaxy and P i is the initial spin period.R does not strongly depend on the exact critical density.The event rate is low because the central density increase is small if the initial spin is slow.However,equation(6)suggest that these types of events happen at afinite rate,especially when we have millions of galaxies in our view.While the accretion power in astrophysics has been stressed in many astronomical environments,equation(6)suggest that the“spin-down power”is not negligible.The spin-down power can apply to any rotating systems with a critical point,not limited to quark-hadron phase transitions,but include Kion or Pion condensations inside neutron stars.Even for a rotating white dwarf the spin-down power alone may trigger a type Ia supernova as the Chandraseckhar mass limit depends on the rotational velocity.3.2CatastrophicIf the phase transition is catastrophic,it may happen on a time scale of sec-onds.In such a short time the star contracts from a radius of∼15km to∼10 km,associated with a sudden spin up.Most importantly,the gravitational energy releasedE∼GM2R ≃1053∆Rluminosity of∼1035ergs s−1.Note that it is25times more luminous than the sun,and it is not necessarily in a binary system12.While thefluid core of the star is contracting,the solid crust may have stress built up in it,and the cracking of the crust can release bursts of energy13.4ObservationsIn this section we confront theoretical predictions with observations.Radio pulsars constitute only a small fraction of all neutron stars because of the beaming nature of their radio emissions,and hence are not the best place to look for the signatures of the phase transition.So far only3pulsars have reliably measured n.Five glitches for Crab pulsar,and7for Vela are recorded with measured Q.Many more are needed to see the continuous phase transi-tion in radio pulsars.4.1Soft Gamma RepeatersSoft Gamma Repeaters(SGRs)are X-ray transient sources(with∼20keV photons)associated with young(104yr)supernova remnants(SNRs).They are usually also quiescent X-ray emitters(with kT∼1keV,L X∼1035ergs s−1). So far4SGRs have been discovered in the Galaxy,and1in the Large Mag-ellanic Cloud.Two SGRs showΩ/2|˙Ω|(∼103yrs)<SNR age(∼104yrs)14. Since many more Anomalous X-ray Pulsars(AXPs)share some properties of SGRs,it seems that our prediction in previous section that we should be able to see one at a time in our Galaxy is an underestimate.Note however that if the initial spin of a neutron star is2ms rather than20ms(that of the Crab pulsar),we get100times more event rate of phase transition.Fast initial spin has indeed been suggested to produce strong magneticfields13and slow down neutron stars much faster than Crab-type pulsars.Radio astronomers may have been biased toward Crab-type pulsars when picking up neutron stars. 4.2Gamma-Ray BurstsGRBs are energetic explosions with total energy1051−1054erg(if isotropic), most of which is released with100keV to a few MeV photons.The time scales range from milliseconds to minutes.The event rate is estimated to be 10−5yr−1galaxy−1if the emission is isotropic,and can be much higher if the emission is highly beamed.We note that the event rate in equation(6)can still account for the GRBs even if they are beamed,and the faster initial spins of the neutron stars naturally offer large angular momentum for the sake of wsllwi:submitted to World Scientific on February1,20085beaming the electromagnetic radiations.Gravity wave detectors such as LIGO may be able to observe gravity waves associated GRBs,and tell which is the correct model.However,the gravity wave is emitted more or less isotropically while the electromagnetic radiation is likely to be highly beamed(with a beaming factor100–1000)in the angular momentum direction.Hence,LIGO may need to accumulate100–1000events before seeing a gravity wave signal at the same time of a GRB.5ConclusionsThe accretion power in astrophysics has been stressed over decades,while the “spin–down power”is often neglected.Here we show that,in any astrophysical systems with angular momentum and a critical point,the spin–down power can drive the system to the critical point at a small butfinite probability. If the transition to critical state is energetic enough to be seen from distant galaxies,we can observe these events regularly,as in the case for the signatures of quark deconfinement phase transitions in radio pulsars,SGRs,and GRBs. AcknowledgmentsI thank Peter Williams for help with the manuscript.References1.J.H.Taylor,L.A.Fowler and P.M.McCulloch,Nature277,437(1979)2.H.W.Kroto et al,Nature318,162(1985)3.S.L.Shapiro and S.A.Teukolsky,Black Holes,White Dwarfs,and Neu-tron Stars,(Wiley,New York,1983)4.J.B.Hartle,Astrophys.J.150,1005(1967)5.J.B.Hartle and K.S.Thorne,Astrophys.J.153,807(1968)6.F.Weber and N.K.Glendenning,Astrophys.J.390,541(1992)7.M.Colpi and ler,Astrophys.J.388,513(1992)8.F.Ma and S.Luo,Bull.American Astron.Soc.28,961(1996).9.F.Ma,Master’s thesis,(Beijing Normal University,1994)10.F.Ma,&B.Xie,Astrophys.J.Lett.462,L63(1996)11.N.K.Glendenning,Phys.Rev.D46,1274(1992)12.F.Ma,Phys.Rev.Lett.81,1983(1998)13.R.C.Duncan and C.Thompson,Astrophys.J.Lett.392,L9(1992)14.C.Kouveliotou et al,Astrophys.J.Lett.510,L115(1999)wsllwi:submitted to World Scientific on February1,20086。
童明雷中国科学院国家授时中心
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童明雷
中国科学院国家授时中心
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飞出太阳系的奇思妙想英语作文600字
飞出太阳系的奇思妙想英语作文600字Escape from the Solar System: Embarking upon an Interstellar Odyssey.Throughout the annals of human history, our gaze has been fixed upon the celestial tapestry above, captivated by the allure of the stars and the boundless expanse of the cosmos. The enigmatic allure of interstellar travel has ignited dreams and fueled imaginations for centuries. While the prospect of venturing beyond our solar system may seem like a futuristic fantasy, recent scientific advancements and audacious proposals are paving the path for the realization of this extraordinary endeavor. Join us as we embark on an exploration of the captivating concept of escaping the solar system and venturing into the uncharted territories of the Milky Way galaxy.A myriad of motivations propels our yearning to escape the confines of our solar system. The pursuit of knowledge and discovery beckons us to unravel the secrets of distantworlds, to probe the nature of celestial bodies, and to fathom the vastness of our universe. The allure of new frontiers ignites a burning desire to explore uncharted territories, to leave an enduring mark upon the tapestry of human exploration. Moreover, the preservation of our species may necessitate the establishment of colonies beyond Earth, safeguarding humanity from existentialthreats such as catastrophic events or resource depletion.Various propulsion systems offer the potential to propel spacecraft beyond the gravitational pull of our solar system. Nuclear fusion, a process that mimics the energy generation of stars, promises immense power and efficiency. Ion propulsion, utilizing electrically charged particles, provides sustained thrust over extended periods. Antimatter propulsion, though still in its infancy, holds the tantalizing possibility of achieving extraordinary speeds.Interstellar travel, however, presents formidable challenges that must be overcome. The vast distances between stars pose a significant obstacle, with even thenearest neighboring stars being light-years away. Consequently, spacecraft must attain colossal speeds to traverse these interstellar gulfs within a reasonable timeframe. The human body, too, must adapt to the rigors of prolonged space travel, enduring the effects of microgravity, radiation exposure, and psychological strain.Despite these formidable hurdles, a collective of brilliant minds is tirelessly working to surmount these challenges. The Breakthrough Starshot initiative, spearheaded by renowned physicist Stephen Hawking, aims to develop ultra-fast spacecraft capable of reaching nearby stars within a generation. The project envisions the use of light sails, propelled by lasers from Earth-based stations, to achieve unprecedented speeds.The implications of escaping the solar system are profound and far-reaching. Establishing colonies on other planets could provide refuge for humanity in the event of a global catastrophe. Access to extraterrestrial resources could alleviate the pressures on our finite Earthly resources. Moreover, interstellar travel would undoubtedlyrevolutionize our understanding of the universe, expanding our knowledge of astrophysics, planetary science, and perhaps even the origins of life itself.As we stand on the cusp of a new era in space exploration, it is imperative that we approach the prospect of escaping the solar system with both excitement and unwavering resolve. The challenges ahead are formidable, but the potential rewards are immeasurable. By harnessing our collective ingenuity, perseverance, and unyieldingspirit of exploration, we can transform the dream of interstellar travel into a tangible reality.The journey beyond our solar system will not be without its trials and tribulations. There will be setbacks, disappointments, and perhaps even moments of despair. Yet, through it all, we must remain steadfast in our conviction that the human spirit is capable of achieving the extraordinary. With each step we take towards the stars, we not only expand our physical horizons but also transcend the limitations of our imagination.As we venture forth into the uncharted realms of space, let us embrace the spirit of exploration that has propelled humanity throughout history. Let us harness the power of our intellect to overcome the obstacles that lie ahead. Let us strive to leave an enduring legacy for future generations, a legacy of courage, curiosity, and the indomitable human spirit.。
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a r X i v :a s t r o -p h /9804332v 2 11 M a y 1998Coalescing Neutron Stars:A Solution to the R-Process Problem ?S.Rosswog 1,F.K.Thielemann 1,M.B.Davies 2,W.Benz 3,T.Piran 41Departement f¨u r Physik und Astronomie,Universit¨a t Basel,Switzerland 2Institute of Astronomy,University of Cambridge,UK 3Physikalisches Institut,Universit¨a t Bern,Switzerland 4Racah Institute for Physics,Hebrew University,Jerusalem,Israel 1.1Introduction Most recent nucleosynthesis parameter studies [3,4,11]place questions on the ability of high entropy neutrino wind scenarios in type II supernovae to produce r-process nuclei for A <110in correct amounts.In addition,it remains an open question whether the entropies required for the nuclei with A >110can actually be attained in type II supernova events.Thus,an alternative or supplementary r-process environment is needed,leading possibly to two different production sites for r-process nuclei:a high entropy,high Y e (neutrino wind in type II supernovae)and a low entropy,low Y e (decompression of neutron star (ns)material)scenario.Further indications for a production site possibly different from SN II arise from observations of low metallicity stars [9].It seems that the production of r-process nuclei is delayed in comparison with the major SN II yields,a fact that would be consistent with the merging scenario of two neutron stars.The tidal disruption of a ns by a black hole and possible consequences for nucleosynthesis has first been studied by Lattimer and Schramm [6,7],the merging of a neutron star binary has been discussed by Symbalisty and Schramm [16].The related decompression of the neutron star material has been investigated by Lattimer et al.[5],Eichler et al.[2],who also discussed various other aspects of such a merging scenario,and by Meyer [10].In the context of numerical simulations the merging event nucleosynthesis has been discussed by Davies etal.[1]and by Ruffert et al.[15].1.2The CalculationsTo investigate the possible relevance of neutron star mergers for the r-process nucleosynthe-sis we perform 3D Newtonian SPH calculations of the hydrodynamics of equal (1.6M ⊙of baryonic)mass neutron star binary coalescences.Starting with an initial separation of 45km we follow the evolution of matter for 12.9ms.We use the physical equation of state of Lattimer and Swesty [8]to model the microphysics of the hot neutron star matter.To test the sensitivity of our results to the chosen approaches and approximations we perform in total 10different runs where we test each time the sensitivity to one property of our model [14].We vary the resolution (∼21000and ∼50000particles),the equation of state (polytrope),the artificial viscosity scheme [12],the stellar masses (1.4M ⊙of baryonic matter),we include neutrinos (free-streaming limit),switch offthe gravitational backreaction force,and vary the initial stellar spins.In addition we test the influence of the initial configuration,i.e.spherical stars versus corotating equilibrium configurations.1.3ResultsWe find that,dependent on the initial spins and strongly dependent on the EOS,between 4·10−3and 4·10−2M ⊙become unbound.Assuming a core collapse supernova rate of 2.2·10−2(year galaxy)−1[13],one needs 10−6to 10−4M ⊙of ejected r-process material per supernova event to explain the observed abundances if type II supernovae are assumed to be the only source.The rate of neutron star mergers has recently been estimated to be 8·10−6(year galaxy)−1(see [17]).Taking these numbers,one would hence need ∼3·10−3M ⊙to ∼0.3M ⊙for an explanation of the observed r-process material exclusively by neutron star mergers.Thus our results for the ejected mass from 4·10−3to 3−4·10−2M ⊙look very promising (see Figure 1).shows the amount of ejecta needed per event if SN II are assumed to be the only sources of the r-process.The asterisk gives the needed ejecta per merging event for the rate of Narayan et al.(1991),the cross for the estimate of van den Heuvel and Lorimer (1996).The event rate is given in year −1galaxy −1,the ejected mass in solar units.As a first step we use the mean properties of all ejected particles (initial corotation)for an r-process calculation.We adopt the following approach:in the very first expansion phase (where ρ>ρdrip ≈4·1011g cm −3)we use the abundances of neutrons,protons,alphas and a representative nucleus provided by the LS-EOS.When the density drops below ρdrip we switch over to a treatment of individual nuclei with a full r-process network following all reac-tions like neutron capture,photo-disintegrations,β-decays etc.as discussed in Freiburghaus et al.[4].Since the representative nucleus at ρdrip was too neutron rich ((Z,A )=(26,155)),we took the most neutron rich nucleus in the network ((Z,A )=(26,73))and assumed theremaining neutrons to be free.Following the trajectory given by the hydro calculation(ex-trapolation for t>12.9ms)we obtained the abundance pattern that is shown in Figure2 together with the observed r-process abundances.Figure2:Comparison of the r-process calculations for a corotating system(initial corotation; line)with the observed abundances(crosses).The observed features of the abundance pattern in the range125<A<200are well reproduced.Especially the peak around A=195is easily reproduced without any tuning of the initial entropy.This approach has two shortcomings:(i)as long as the LS-EOS is used,only one(repre-sentative)nucleus is used instead of an ensemble of nuclei and(ii)weak interactions such as β-decays or e−−,e+−captures on protons and neutrons are disregarded in this early phase. 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