Supernova rates in Abell galaxy clusters and implications for metallicity

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介绍宇宙英语作文

The universe is a vast expanse that has fascinated human beings for centuries.It is the collection of all existing matter and energy,including galaxies,stars,planets,and other celestial bodies.Here is a detailed introduction to the universe in an English essay format.Title:The Enigma of the UniverseIntroduction:The universe,a boundless and aweinspiring concept,has been a subject of wonder and study for as long as humanity has gazed upon the stars.It is the ultimate frontier,a testament to the infinite possibilities that lie beyond our terrestrial realm.Composition of the Universe:The universe is composed of billions of galaxies,each containing billions of stars.Our own galaxy,the Milky Way,is just one of these celestial bodies.Surrounding these stars are planets,some of which,like our Earth,are capable of supporting life.The universe also contains vast amounts of dark matter and dark energy,which,despite being invisible, play a crucial role in the expansion and structure of the cosmos.The Big Bang Theory:The most widely accepted explanation for the origin of the universe is the Big Bang Theory.According to this theory,the universe began as an infinitely dense and hot point, and has been expanding ever since.This event occurred approximately13.8billion years ago and set in motion the creation of all the matter and energy that we observe today.Galaxies and Stars:Galaxies are massive collections of stars,gas,and dust held together by gravity.They come in various shapes and sizes,from spiral galaxies like the Milky Way to elliptical galaxies that are more rounded.Stars,the powerhouses of galaxies,are born in nebulae and can live for billions of years,undergoing various stages of evolution before they die, sometimes in spectacular supernova explosions.Planets and Solar Systems:Planets are celestial bodies that orbit stars.They are diverse in nature,ranging from rocky terrestrial planets like Earth to gas giants like Jupiter.Our solar system,with its eight planets,is just one example of the many solar systems that exist within galaxies.Life in the Universe:The search for extraterrestrial life is an ongoing endeavor.While Earth is the only known planet to harbor life,the vastness of the universe suggests that the conditions necessaryfor life could exist elsewhere.Scientists are continually searching for signs of life on other planets,moons,and even in the interstellar medium.The Expansion and Fate of the Universe:The universe is not static it is in a state of constant expansion.This expansion is driven by dark energy,a mysterious force that is causing the universe to stretch at an accelerating rate.The ultimate fate of the universe is still a topic of debate among cosmologists,with possibilities ranging from a Big Freeze to a Big Rip.Conclusion:The universe is a complex and dynamic entity that continues to reveal its secrets to us.As our understanding of the cosmos grows,so too does our appreciation for the intricate balance of forces that govern its existence.The universe is a reminder of our place in the grand scheme of things and the boundless potential for discovery that lies ahead. Further Exploration:The study of the universe is a collaborative effort that spans disciplines and cultures. From the earliest stargazers to modern astronomers and astrophysicists,the quest to understand the universe is a testament to human curiosity and our desire to explore the unknown.As technology advances,we can expect to uncover even more about the cosmos and our place within it.。

自考英语(二)教材课文翻译

自考英语(二)课文翻译Unit One What Is a Decision ?何为决策 ?A decision is a choice made from among alternative courses of action that are available. The purpose of making a decision is to establish and achieve organizational goals and objectives. The reason for making a decision is that a problem exists, goals or objectives are wrong, or something is standing in the way of accomplishing them.决策是一种选择，来自可以获得的、任择其一的行动步骤。

作决策的意图是要确立和实现机构的目标和目的。

作决策的原因是有问题存在、目标和目的不正确、或者有某种东西妨碍目标或目的的实现。

Thus the decision-making process is fundamental to management. Almost everything a manager does involves decisions, indeed, some suggest that the management process is decision making. Although managers cannot predict the future, many of their decisions require that they consider possible future events. Often managers must make a best guess at what the future will be and try to leave as little as possible to chance, but since uncertainty is always there, risk accompanies decisions . Sometimes the consequence s of a poor decision are slight; at other times they are serious.因此，作决策的过程对管理人员来说至关重要。

外星人是否存在的英语作文

外星人是否存在的英语作文英文回答：The Existence of Extraterrestrial Life: A Scientific Inquiry.The question of whether extraterrestrial life exists has captivated humanity for centuries. From ancient myths and folklore to modern scientific inquiry, the search for intelligent beings beyond Earth continues to inspire awe and speculation.From a scientific perspective, the search for extraterrestrial life is guided by two fundamental principles: the Drake equation and the Fermi paradox. The Drake equation attempts to estimate the number of potentially habitable planets in the Milky Way galaxy based on factors such as the rate of star formation, the fraction of stars with planets, and the likelihood of those planets supporting life. While the estimates vary widely, theequation suggests that there could be a significant number of habitable planets in our galaxy.The Fermi paradox, on the other hand, poses the question: "If life is so common, why haven't we detected it yet?" Despite decades of radio telescope observations, space exploration missions, and SETI (Search for Extraterrestrial Intelligence) programs, we have yet to establish contact with extraterrestrial civilizations. This apparent contradiction has led to a range of hypotheses, including the Great Filter theory, which suggests that there are barriers that prevent most civilizations from advancing to a detectable level of intelligence.Recent astronomical discoveries have provided further impetus to the search for extraterrestrial life. The confirmation of exoplanets, planets outside our solar system, has shown that our Milky Way galaxy is teeming with planetary systems. Moreover, the discovery of potentially habitable exoplanets, such as TRAPPIST-1 and Proxima Centauri b, has raised the possibility that life may exist not only on Earth but also on nearby planets.中文回答：外星人是否存在，一个科学探究。

GRE阅读高频机经原文：冰川沉积物

GRE阅读高频机经原文：冰川沉积物GRE阅读高频机经原文：冰川沉积物GRE阅读高频机经原文：冰川沉积物14. 冰川沉积物Tills are commonly classi?ed according to the perceived process of deposition. However, it is increasingly recognised that this classi?cation, which is mainly based on macroscopic ?eld data, has severe limitations. At the same time the concept of the deforming glacier bed has become more realistic as a framework for discussing tills and their properties, and this (tectonic) concept is irreconcilable with the existing (depositional) till classi?cation scheme. Over the last 20 years large thin sections have been used to study tills, which has provided new insights into the textural and structural properties of tills. These results have revolutionised till sedimentology as they show that, in the main, subglacial tills possess deformational characteristics. Depositional properties are rare.Based on this new insight the process of subglacial till formation is discussed in terms of glacier/ice sheet basal velocity, clay, water and carbonate content and the variability of these properties in space and time. The end result of this discussion is: till, the deforming glacier bed. To distinguish subglacial till from depositional sedim ents the term ‘tectomict’ is proposed. Within the single framework of subglacial till as the deforming glacier bed, many textural, structural and geomorphological features of till beds can be more clearly and coherently explained and understood.GRE阅读高频机经原文及答案：云和气候变化预测15. 云和气候变化预测 1996年04月北美 D9604As of the late 1980’s, neither theorists nor large-scale computer climate models could accurately predict whether cloud systems would help or hurt a warming globe. Some studies suggested that a four percent increase in stratocumulus clouds over the ocean could compensate for a doubling in atmospheric carbon dioxide, preventing a potentially disastrous planetwide temperature increase. On the other hand, an increase in cirrus clouds could increase global warming.That clouds represented the weakest element in climate models was illustrated by a study of fourteen such models. Comparing climate forecasts for a world with double the current amount of carbon dioxide, researchers found that the models agreed quite well if clouds were not included. But when clouds were incorporated, a wide range of forecasts was produced. With such discrepancies plaguing the models, scientists could not easily predict how quickly the world’s climate would change, nor could they tell which regions would face dustier droughts or deadlier monsoons.15.1. The author of the passage is primarily concerned with(A) confirming a theory(B) supporting a statement(C) presenting new information(D) predicting future discoveries(E) reconciling discrepant findings15.2. It can be inferred that one reason the fourteen models described in the passage failed to agree was that(A) they failed to incorporate the most up-to-date information about the effect of clouds on climate(B) they were based on faulty information about factors other than clouds that affect climate(C) they were based on different assumptions about the overall effects of clouds on climate(D) their originators disagreed about the kinds of forecasts the models should provide(E) their originators disagreed about the factors other than clouds that should be included in the models15.3. It can be inferred that the primary purpose of the models included in the study discussed in the second paragraph of the passage was to(A) predict future ch anges in the world’s climate(B) predict the effects of cloud systems on the world’s climate(C) find a way to prevent a disastrous planetwide temperature increase(D) assess the percentage of the Earth’s surface covered by cloud systems(E) estimate by how much the amount of carbon dioxide in the Earth’s atmosphere will increase15.4. The information in the passage suggests that scientists would have to answer which of the following questions in order to predict the effect of clouds on the warming of the globe?(A) What kinds of cloud systems will form over the Earth?(B) How can cloud systems be encouraged to form over the ocean?(C) What are the causes of the projected planetwide temperature increase?(D) What proportion of cloud systems are currently composed of cirrus of clouds?(E) What proportion of the clouds in the atmosphere form over land masses?答案：B C A AGRE阅读高频机经原文及答案：Supernova16. Supernova D 89-12Astronomers observe a supernova that is dimmer than expected because of dust screening，If a supernova (the explosion of a massive star) triggered star formation from dense clouds of gas and dust, and if the most massive star to be formed from the cloud evolved into a supernova and triggered a new round of star formation, and so on, then a chain of star-forming regions would result. If many such chains were created in a differentially rotating galaxy, the distribution of stars would resemble the observed distribute in a spiral galaxy.This line of reasoning underlies an exciting new theory of spiral-galaxy structure. A computer simulation based on this theory has reproduced the appearance of many spiral galaxies without assuming an underlying density wave, the hallmark of the most widely accepted theory of the large-scale structure of spiral galaxies. That theory maintains that a density wave of spiral form sweeps through the central plane of a galaxy, compressing clouds of gas and dust, which collapse into stars that form a spiral pattern.。

超新星纪元词语

以下是90个超新星纪元的词语以及它们的译文：1.超新星纪元- Supernova Age2.星际物质- Interstellar Matter3.星云- Nebula4.恒星- Star5.黑洞- Black Hole6.脉冲星- Pulsar7.星系- Galaxy8.旋臂- Spiral Arm9.恒星系- Stellar System10.双星- Binary Star11.星团- Star Cluster12.星云团- Nebula Cluster13.星际空间- Interstellar Space14.星尘- Stardust15.星系团- Galaxy Cluster16.超星系团- Supercluster17.宇宙射线- Cosmic Ray18.反物质- Antimatter19.高能射线- High-energy Radiation20.量子力学- Quantum Mechanics21.引力波- Gravitational Wave22.宇宙微波背景辐射- Cosmic Microwave Background Radiation23.暗物质- Dark Matter24.暗能量- Dark Energy25.星系核- Galaxy Core26.黑洞吞噬- Black Hole Accretion27.恒星演化- Stellar Evolution28.核合成- Nucleosynthesis29.星系碰撞- Galaxy Collision30.恒星爆炸- Stellar Explosion31.引力透镜- Gravitational Lensing32.宇宙网- Cosmic Web33.反物质粒子- Antimatter Particles34.高纬宇宙模型- High-dimensional Cosmic Model35.宇宙常数- Cosmological Constant36.宇宙密度- Cosmic Density37.宇宙膨胀- Cosmic Expansion38.宇宙学红移- Cosmological Redshift39.大爆炸理论- Big Bang Theory40.弦理论- String Theory41.相对论- Relativity42.量子力学- Quantum Mechanics43.弦理论- String Theory44.卡鲁扎-克莱因理论- Kaluza-Klein Theory45.高维时空- Higher-dimensional Spacetime46.虚时间- Virtual Time47.宇宙微波背景辐射- Cosmic Microwave Background Radiation48.标准宇宙模型- Standard Cosmological Model49.星系团- Galaxy Cluster50.超星系团- Supercluster51.丝状结构- Filamentary Structure52.大尺度结构- Large-scale Structure53.哈勃常数- Hubble Constant54.引力波- Gravitational Wave55.黑洞信息悖论- Black Hole Information Paradox56.夸克星- Quark Star57.反物质星- Antimatter Star58.原子核- Atomic Nucleus59.量子纠缠- Quantum Entanglement60.高温高压状态方程- High-temperature and high-pressure equation ofstate61.星系演化- Galaxy Evolution62.星系动力学- Galaxy Dynamics63.星际物质循环- Interstellar Matter Cycle64.恒星形成- Star Formation65.分子云- Molecular Cloud66.星际空间气体- Interstellar Gas67.星际尘埃- Interstellar Dust68.星系核活动- Active Galactic Nucleus69.射电星系- Radio Galaxy70.光学星系- Optical Galaxy71.X射线星系- X-ray Galaxy72.恒星团- Star Cluster73.双星系统- Binary Star System74.变星- Variable Star75.新星- Nova76.超新星- Supernova77.中子星- Neutron Star78.脉冲星- Pulsar79.黑洞候选体- Black Hole Candidate80.高光度蓝变星- High-luminosity Blue Variable Star81.超巨星- Supergiant Star82.红巨星- Red Giant Star83.黄矮星- Yellow Dwarf Star84.白矮星- White Dwarf Star85.恒星演化模型- Stellar Evolution Model86.星际物质分布- Interstellar Matter Distribution87.分子光谱学- Molecular Spectroscopy88.高能天体物理学- High-energy Astrophysics89.天体化学- Astrochemistry90.宇宙射线物理学- Cosmic Ray Physics。

天文学家发现另一颗像塔比星那样闪烁的恒星

天文学家发现另一颗像塔比星那样闪烁的恒星Lisa Grossman到目前为止，天文学家发现银河系中还有另外一颗奇异闪烁的恒星。

天文学家使用位于智利的望远镜发现了一颗明暗变化奇异的恒星，这让人想起了塔比星——一颗曾经被认为拥有外星超级结构体的恒星。

超级结构体的想法首先在2015年提出，不久之后被撤销，主要是因为有数据显示这种亮度的衰减有可能是尘粒遮掩住恒星光线所致。

新近发现的这颗恒星的行为也可能不是外星生命所为。

但是它实在令人困惑，来自于巴西圣卡塔琳娜州联邦大学的天文学家Roberto Saito 说道。

他和他的同事于2018年11月6日在上就这颗恒星奇异的闪烁作了报告。

“我们不知道那个物体是什么。

”他说道，“那实在太有意思了。

”这颗恒星或可拥有一些绕行的残骸，这些残骸会定期地挡住星光，但是Saito 和他的同事们表示他们需要更多的观测确定那是否可能，或者这种奇异的闪烁是由其他原因所导致的。

当研究团队从VISTA 望远镜（位于智利北部的阿塔卡马沙漠）的数据中锁定这个目标时，研究人员一直在搜寻那些随着爆发而突然增亮的超新星和恒星。

这些数据只是针对银河中心大规模探查数据的一部分，它们被称为银河VISTA 变量，或者VVV。

与增亮恰恰相反，这颗恒星突然变暗。

研究团队将它称为VVV-WIT-07，这到底是什么呢？从2010年到2018年，这颗恒星亮度的增加与减少从没有固定模式。

这种亮度模式的缺乏与塔比星十分相像，除了VVV-WIT-07的亮度可下降达80%，而塔比星的亮度只会下降20%。

此外还有一颗被称为J1407的闪烁恒星，它可能更为匹配。

这颗恒星周期性变暗程度可达95%，来自于美国纽约罗切斯特大学的天文学家Eric Mamajek 和他的同事在2012年对此作过报告。

天文学家认为J1407的一颗绕轨运行的行星具有庞大的星环系统，它能够周期性地遮掩恒星。

星体的消亡【英文】

Planetary Nebula IC 418 (Spirograph Nebula)
The Eskimo Nebula
White Dwarfs
Degenerate stellar remnant (C,O core) Extremely dense: 1 teaspoon of WD material: mass ≈ 16 tons!!! Chunk of WD material the size of a beach ball would outweigh an ocean liner!
Black Holes
Just like white dwarfs (Chandrasekhar limit: 1.4 Msun), there is a mass limit for neutron stars:
Subrahmanyan Chandrasekhar,
(1910-1995, Indian-born American):
In 1983 won Nobel Prize in Physics for his theoretical studies of the physical processes of importance to the structure and evolution of the stars. The Chandra X-Ray Space Telescope is named in his honor.
The Famous Supernova of 1987: SN 1987A
Before At maximum
Unusual type II Supernova in the Large Magellanic Cloud in Feb. 1987

银河英文作文素材高中

银河英文作文素材高中The Milky Way, also known as the Galaxy, is a barred spiral galaxy that is home to our solar system, along with billions of other stars and their planetary systems. It is a vast and awe-inspiring expanse of space that has captured the imagination of humans for centuries.The Milky Way is estimated to be about 100,000 light-years in diameter, and it is thought to contain between 100 billion and 400 billion stars. The exact number isdifficult to pin down, as many stars are too faint to be observed directly. This immense number of stars gives the Milky Way its characteristic appearance as a band of light stretching across the night sky.One of the most fascinating aspects of the Milky Way is the presence of dark matter. This mysterious substance is thought to make up about 85% of the total mass of the galaxy, yet it does not emit or reflect any electromagnetic radiation, making it invisible to telescopes. Its presenceis inferred from its gravitational effects on visible matter.The Milky Way is also home to a variety of celestial objects, including nebulae, star clusters, and supernova remnants. These objects provide valuable insights into the processes of star formation and evolution, and they are the focus of much research and observation by astronomers.The study of the Milky Way is ongoing, and new discoveries are constantly being made. From the structure and dynamics of the galaxy to the search for exoplanets and signs of extraterrestrial life, there is always something new and exciting to learn about our cosmic home.。

50年来最亮超新星爆炸英国境内可用望远镜观看(英语学习).doc

50年来最亮超新星爆炸英国境内可用望远镜观看（英语学习）50年来最亮超新星爆炸英国境内可用望远镜观看There will be an once-in-a-lifetime event in the night sky over the next few days – as a star exploding 21 million light years away becomes so bright it will be visible through binoculars across Britain。

The supernova is predicted to reach its brightest between September 9 and 12, and will be the brightest since 1954, visible all over Britain, weather permitting. A team of scientists at Oxford University are tracking it using the Hubble Space Telescope。

Dr Mark Sullivan, the astrophysicist leading the Oxford team examining the supernova, said: “This is accessible to anyone with a decent pair of binoculars. For many it could be a once in a lifetime chance to see a supernova blossom and then fade before their eyes. We may not see another like it for over 100 years.”It will appear bluish-white, just above and to the left of the last two stars in the Big Dipper. Watchers are advised to stay away from street lights for maximum visibility.The matter from the explosion will eventually form new stars and planets. Such events, which include one in five supernovae, provide scientists with essential information on how the universe expands。

The effect of supernova heating on cluster properties and constraints on galaxy formation m

a r X i v :a s t r o -p h /9810008v 1 1 O c t 1998Mon.Not.R.Astron.Soc.000,000–000(0000)Printed 1February 2008(MN L A T E X style ﬁle v1.4)The eﬀect of supernova heating on cluster properties andconstraints on galaxy formation modelsK.K.S.Wu,1,3A.C.Fabian 1and P.E.J.Nulsen 21Institute of Astronomy,Madingley Road,Cambridge CB30HA2Department of Physics,University of Wollongong,Wollongong NSW 2522,Australia 3kwu@ABSTRACTModels of galaxy formation should be able to predict the properties of clusters of galaxies,in particular their gas fractions,metallicities,X-ray luminosity-temperature relation,temperature function and mass-deposition-rate function.Fitting these prop-erties places important constaints on galaxy formation on all scales.By following gas processes in detail,our semi-analytic model (based on that of Nulsen &Fabian 1997)is the only such model able to predict all of the above cluster properties.We use realistic gas fractions and gas density proﬁles,and as required by observations we break the self-similarity of cluster structure by including supernova heating of intracluster gas,the amount of which is indicated by the observed metallicities.We also highlight the importance of the mass-deposition-rate function as an independent and very sensitive probe of cluster structure.Key words:galaxies:clusters:general –galaxies:formation –galaxies:evolution –cooling ﬂows –X-rays:galaxies1INTRODUCTIONOur understanding of galaxy formation through the hierar-chical clustering of gas and dark matter (DM)has improved greatly over the past decade.The aim of models of galaxy formation is to account for the properties of all structure,from the ﬁrst dwarf galaxy to the rich clusters of galax-ies that are virialising now.The collapse of the dominant dark matter is relatively well understood,so that the ma-jor current problem is to model the complex gas processes that take place within collapsed and collapsing DM halos.Despite their success in accounting for some properties of galaxies,many semi-analytical models do not predict cor-rectly the properties of groups and clusters of galaxies.In particular,these models should predict gas fractions,metal-licities,the X-ray luminosity-temperature (L X −T )relation,the temperature function and the mass-deposition-rate (˙M)function of clusters.One problem is that the gas fraction in clusters,which is observed to be in the range 10–20per cent (White et al.1993b;White &Fabian 1995;David,Jones &Forman 1995;White,Jones &Forman 1997;Evrard 1997),is under-estimated by those models that have low baryon fractions (e.g.,most of the values considered by Kauﬀmann,White &Guiderdoni (1993),Cole et al.(1994),Heyl et al.(1995),Kauﬀmann &Charlot (1998)and Baugh et al.(1998)).In this paper we show that additional heat input tothe intracluster gas,which in our ﬁducial model we take tobe due to supernovae,can consistently account for the ma-jor X-ray properties of groups and clusters of galaxies.This has a similar eﬀect to ‘preheating’as invoked by other au-thors (Kaiser 1991;Evrard &Henry 1991;Metzler &Evrard 1994;Navarro,Frenk &White 1995;Bower 1997;Jones et al.1998).A well-known problem addressed by preheating is the slope of the L X −T relation.Models and simulations which do not involve preheating (and in general those which inves-tigate galaxy properties do not)are generally ‘self-similar’and give L X ∝T 2(Kaiser 1986),whereas clusters are ob-served to follow L X ∝T 3(David et al.1993).Models which preheat the gas in clusters generally break the self-similarity.For example,a constant excess speciﬁc energy can have a large eﬀect in the shallow potential wells of groups,while having little eﬀect on the largest clusters.The excess energy raises the temperature as well as the potential energy of the gas by pushing it outwards,thereby ﬂattening the gas den-sity proﬁle.This lowers L X and steepens the relationship between L X and T .During galaxy formation gas is heated and possibly ejected from galaxies by supernovae.It retains most of this ‘excess energy’as thermal and gravitational potential energy (and possibly kinetic energy)as it passes through the col-lapse hierarchy,eventually becoming part of the intergalactic medium in groups and clusters.Gas that is ejected from a galaxy is expected to recollapse with the next ‘major merger’c0000RAS2K.K.S.Wu et al.(which in our model is the doubling,at least,of the mass of the halo that the galaxy resides in).This is reasonable since ejected gas would encounter the inter-galactic medium which subsequently forms part of a larger halo.In ourﬁdu-cial model the only source of heating and metal enrichment is Type II supernovae(SNe II)associated with star formation (Nulsen&Fabian1995,1997;hereafter NF95and NF97). There is some evidence that most of the metals in intraclus-ter gas came from SNe II rather than SNe Ia(Mushotzky et al.1996;Nagataki&Sato1998),but a further reason for our assumption is because while both types inject about the same amount of energy,SNe Ia inject about10times more iron than SNe II.Hence for the iron abundance mea-sured in intracluster gas,the associated energy injection is maximised by using only SNe II.We assume an energy in-jection of4×1050erg per supernova(Spitzer1978)which is not radiated locally.The mean mass of iron produced per supernova is0.07M⊙,which leads to3.7keV/particle ex-cess speciﬁc energy in gas with solar iron abundance.By choosing the initial metallicity in groups when they areﬁrst formed to be a suitable value,the iron abundance of clusters in our model is Z≈0.3Z⊙which corresponds to about1.1 keV/particle of excess energy.The semi-analytical model we use is based on that de-scribed in NF97,with an improved cosmological model and a more accurate form for dark matter halos.The model pays particular attention to gas processes,explicitly including the eﬀects of coolingﬂows in its treatment of hot gas.When hot gas has had suﬃcient time to radiate its thermal energy it is assumed to preferentially form low mass stars,eﬀectively baryonic dark matter(BDM),as observed in coolingﬂows in clusters.We assume that dark matter halos follow the NFW proﬁle(Navarro,Frenk&White1997;hereafter NFW97). Gas in the resulting potential wells is assumed to be isother-mal and in hydrostatic equilibrium.The model clusters turn out to have gas density proﬁles closely resembling those in observed clusters.In this paper we use an open cosmology withΩ0=0.3, H0=50km s−1Mpc−1and a cosmological constant of zero. Densityﬂuctuations are obtained from a CDM model with primordial spectral index of n=1,normalised to makeσ8= 0.7.This normalisation,which is slightly lower than some estimates based on cluster numbers,is discussed in section3. We note that our results would be largely unchanged in a ﬂat cosmology with the sameΩ0,since the mass function of clusters today would be the same.Likewise,our conclusions do not depend on when the excess energies were injected or the exact history of the clusters and their progenitors.We do however assume that the supernovae injected their energy into virialised gas,as opposed to the uncollapsed IGM.2DESCRIPTION OF THE MODELThe two main changes from the model described in NF97are the use of an open cosmology and the improvement of the DM and gas proﬁles.The mass of a halo is deﬁned as that inside the virial radius,r200,and the mean density inside r200 is required to be200times the background density of anΩ= 1universe of the same age.(This is marginally diﬀerent from NFW97,but follows the spherical collapse model strictly.) We use the NFW proﬁle(NFW97)which takes the form ρ(r)=ρsx+1kTφ(r) ,(3) whereµm H is the mean mass per particle in the gas,T is its temperature and k is Boltzmann’s constant.Inserting the expression for the potential givesρg(r)=A(1+x)η/x(4) where A is a constant andη=µm Hα/(kT).The above pro-ﬁle,which we shall refer to as the NFW-gas proﬁle,was shown by Makino et al.(1997)to closely approximate the conventionalβ-model(withβ=η/15).It tends to Aeηin the centre and to A for large x.Thus A is,in practice,very small and the plateau at large x is not noticeable.The pa-rameterαhas the same units as velocity dispersion squared, thus it is apparent thatηis closely related to the widely-used parameterβ,the ratio of the DM kinetic energy to the thermal energy of the gas when both are isothermal.The NFW-gas proﬁle has beenﬁtted to the surface brightness proﬁles of observed clusters and it models most clusters very well(Ettori&Fabian1998).Values ofηin the largest clusters which have coolingﬂows(suggesting they are in a relaxed state,in contrast to non-coolingﬂows;Buote& Tsai1996)average about10.5,with a standard deviation of about1.0(Ettori,private communication).Direct compar-ison shows that the gas proﬁle forη=10.5closely follows the NFW proﬁle from x=0.4to3.The proﬁles diﬀer in-side x=0.4due to theﬂat core of the NFW-gas proﬁle, which implies that the gas fraction increases as a function of radius,as observed in real clusters(e.g.White,Jones& Forman1997).This last eﬀect becomes more pronounced and spreads to larger radii for smaller values ofη,the major cause of which will be heating by supernovae.Sinceηgives both the gas temperature and the slope of the gas density proﬁle,it is the structural parameter through which supernova heating exerts its inﬂuence on cluster prop-erties.The procedure for settingηis as follows.We postulate that the total speciﬁc energy of the gas(thermal plus gravi-c 0000RAS,MNRAS000,000–000Supernova heating3 tational)is proportional to the speciﬁc gravitational energyof the DM,and that any excess speciﬁc energy from super-nova heating is added to the above gas energy,as its nameimplies.i.e.,3kTM gas=K 1M DM+E excess,(5)whereρDM is the DM density,which follows the NFW pro-ﬁle,M gas and M DM are the total gas and DM masses,andE excess is the excess speciﬁc energy.The volumes of integra-tion are spheres of radius r200.Given the constant K,it iseasy to show thatηis only a function of c and E excess.Theconstant of proportionality K is calibrated so thatηis closeto the observed value of10.5for the largest clusters,whenE excess=0.We use the value K=1.2.(Note thatηvariesby around0.5depending on collapse redshift,through itsdependence on c.)The reason for matching to the largest clusters is that if supernova heating does occur,we expectit to have least eﬀect on the largest clusters.As c varieslittle over cluster masses,this method ensures that clusters are self-similar when there is no excess energy(i.e.,c andηare roughly constant).The trends for c andηare to increaseslightly with decreasing mass,over all masses in our model (see below).The mass deposition rates of clusters are estimated byﬁnding the radius r cool at which the cooling time is equal to the time∆t to the next major merger(see below)or thepresent,and dividing the gas mass enclosed by∆t to give ˙M.For clusters with coolingﬂows,i.e.,those with signiﬁcant˙M,the hot gas which cools does not form stars but BDM.The Cole&Kaiser(1988)block model is used to simu-late the merging history of dark matter halos.The smallest masses in the hierarchy are1.5×1010M⊙and there are20 levels of hierarchy so that the total mass in one collapse tree is7.9×1015M⊙.When a‘block’in the hierarchy virialises, it merges into one halo both older halos and previously un-collapsed material.The new average metallicity and excess energy of the gas can therefore be calculated.Since blocks double in mass up the hierarchy,each collapse of a block roughly corresponds to a major merger.As already men-tioned,we set the metallicities in groups to be high without considering the implications of this for star formation.Halos with masses in the range15–120×1012M⊙are given initial iron abundances of Z=0.5Z⊙˙(This implies that the gas in some of the smaller halos is unbound.)As a result the av-erage metallicities(for a given mass)range from0.3Z⊙for clusters of mass250×1012M⊙to0.25Z⊙for the largest clus-ters.The range of scatter in metallicities is≈0.1Z⊙.These are in good agreement with the recent ASCA measurements by Fukazawa et al.(1998)of iron abundances in40nearby clusters and the measurements of Allen&Fabian(1998).The gas fraction of the clusters in our model lie within one per cent of14per cent.3RESULTS AND DISCUSSIONTo illustratethe eﬀect of heating from supernovae,we dis-play in Fig.1the L X-T distributions before and after the inclusion of supernova heating.We superimpose on the dis-tributions the power lawﬁt obtained by David et al.(1993), for bolometric luminosities.The excess energies bring the Figure 1.Contour plots of the luminosity-temperature distri-bution,without heating by supernovae(dotted lines)and with supernova heating(solid lines).The contours are spaced at equal logarithmic intervals.The long straight line is the bestﬁt(for bolometric luminosities)taken from David et al.(1993).The dis-tribution obtained without heating is roughly parallel to the short line segment which follows L X∝T2.In this case the smallest clusters are overluminous by an order of magnitude.The excess energies bring the smaller clusters into agreement with data. smaller clusters into agreement with the observed correla-tion,by increasing their temperature,ﬂattening their den-sity proﬁles and thereby decreasing their luminosities.For clusters of mass2.5×1014M⊙,ηdecreases to around9.The spread in the L X-T distributions are signiﬁcant and arise naturally in our simulation from the diﬀerent formation his-tories of the clusters.For comparison with Fig.1,if we halve the excess en-ergies injected,the average luminosity of a2×107K cluster rises to5×1043erg s−1.Doubling the excess energies causes most of the clusters with T<3×107K to be unbound,which clearly disagrees with data,and roughly halves the luminos-ity of3×107K clusters.In future work we will investigate whether restricting the heating to the core of clusters can de-crease the excess energies required(preliminary results sug-gest that this could reduce the total energy requirements by about a third).In Figs.2and3we show the X-ray luminosity function (XLF)and temperature function respectively.The curves plotted for comparison are the bestﬁt Schechter function to the ROSAT Brightest Cluster Sample(BCS)bolometric luminosity function,obtained by Ebeling et al.(1997),and the best power lawﬁt to the temperature function obtained by Edge et al.(1990).The errors in the BCS XLF are very small,while the temperature function is currently uncertain by factors of around2or3.A problem which follows from an incorrect slope of the L X-T relation is that if the temper-ature functionﬁts the data reasonably well,then the XLF is too steep compared to data(e.g.Kitayama and Suto1996). Correcting the L X-T relation thus improves the slope of the XLF signiﬁcantly,though it is still slightly steeper than ob-served.Estimates ofσ8from cluster abundances in general use a theoretically derived mass function and assume some mass-c 0000RAS,MNRAS000,000–0004K.K.S.Wu etal.Figure 2.The X-ray luminosity function (XLF)from the model with supernova heating.The curve is the best ﬁt Schechter func-tion to the ROSAT Brightest Cluster Sample (BCS)bolometric luminosity function (Ebeling et al.1997).Figure 3.The temperature function from the model with su-pernova heating.The power law ﬁt to the temperature function obtained by Edge et al.(1990)is plotted.temperature (M −T )relation in order to compare with an observed temperature function.The calibration of the M −T relation is thus crucial to the results,especially as the tem-perature function has a very steep slope.We ﬁnd that with zero excess energy our model clusters obey the simple esti-mate (appropriate for isothermal r −2gas and DM density proﬁles)of GM 200µm H(6)to within a few per cent,where M 200is the total mass within r 200.Supernova heating raises the temperature slightly for small clusters.For a cluster of mass 4.9×1014M ⊙collapsing at z =0the temperature increases from 3.5×107K to 3.8×107K in the model described,close to 10per cent higher.The resulting temperatures in our model are anecessaryFigure 4.The smoother curve is the ˙Mcumulative function from our model with supernova heating,and is compared to the function taken from Peres et al.(1997)but with the age of clusters changed to 6Gyr,as explained in the text.We have also excluded clusters with T <2×107K;when all clusters are allowed to contribute,the function increases below 50M ⊙yr −1,rising to 6×10−5Mpc −3at 10M ⊙yr −1,but such clusters would not be included in the observed sample.consequence of ﬁtting the L X −T relation.In a recent paper,Eke et al.(1998)used a more elaborate form of Equation 6and included scatter in the M-T relation,which brought down the predicted σ8.With our CDM shape parameter of Γ=Ω0h exp(−Ωb (1+1/Ω0))=0.12their Fig.7predicts a value of σ8≈0.75.Since preheating was not included,our value of σ8=0.7appears consistent with their results.Turning to the mass deposition rates,we display the ˙Mcumulative space density in Fig.4.We have excluded clus-ters with temperatures less than 2×107K since such objects would be too faint in the 2–10keV band to be included in the sample used by the two papers below.Our result agreesvery well with the ˙Mcumulative function obtained by Edge,Stewart &Fabian (1992)and lies slightly lower than that shown in Peres et al.(1997).The systematic uncertaintiesin measurements of ˙Min clusters are at present around a factor of 2.In particular the age of a cluster since its last major merger is unknown and in determining r cool the age of the universe is generally used.Lowering this age in the analysis of Peres et al.(1997)from 13Gyr to 6Gyr,which is the typical age of a 5keV cluster in our model,lowers r cooland more than halves the values of ˙Min several clusters (Peres,private communication).In Fig.4we show the cu-mulative function from Peres et al.(1997)recalculated with this change in the age of clusters.There is very good agree-ment for all but small values of ˙M,which is not a serious concern since the clusters and their measurements are both sensitive to small perturbations in this range.The mass deposition rate of a cluster is a highly sensi-tive probe of the gas density inside a radius of ∼0.1Mpc (the typical r cool observed in cooling ﬂows).On the other hand,the luminosity in all but the most massive cooling ﬂows comes from inside a radius ∼r s which is larger thanthe cooling ﬂow region.Therefore L X and ˙Mare indepen-dent probes of the gas density proﬁle at diﬀerent radii,and due to their sensitivity they are eﬃcient at eliminating mod-c0000RAS,MNRAS 000,000–000Supernova heating5els.For example,while we can adjust the overall density inside∼r s by changing the temperature,the ratio of the densities inside the two radii described above have to be cor-rect in order to match both the˙M function and the XLF. We found that models which used gas density proﬁles of the form r−2β(see NF97)overpredicted the˙M function by an order of magnitude or more.The agreement with the avail-able data suggests that the NFW-gas proﬁle is much closer to the right shape.As a further example of the ability of˙M to discrimi-nate between models,without supernova heating weﬁnd an average value of˙M≈100M⊙yr−1for coolingﬂow clusters with L X=6×1043erg s−1which is too high when compared with Fig.2of Peres et al.(1997).However,heating lowers the value to˙M≈30M⊙yr−1,which then agrees with their data. On the other hand,large clusters with L X=1045erg s−1 have the correct˙M with and without ing a hy-drodynamic and N-body simulation,Katz&White(1993) modelled a Virgo-like cluster with cooling of gas included, and obtained an excessively high value of˙M∼400M⊙yr−1. Our results suggest that non-gravitational heating could si-multaneously help solve such a problem.The above results argue forﬂatter gas density proﬁles in small clusters,in-dependently of the L X−T relation.We consider it very promising that by correctlyﬁtting the L X−T relation,the predictions pertaining to˙M naturally agree with the data. 4CONCLUSIONSWe have presented a galaxy formation model in which the X-ray properties of clusters agree well with what is observed. The model is based on that described by Nulsen&Fabian (1997),and uses observed gas fractions and metallicities.Re-alistic gas density proﬁles were used,which sit in potentials given by the NFW proﬁle.In particular,we obtained good ﬁts to the L X−T relation,the X-ray luminosity function, the temperature function and the˙M function,which weﬁnd to be a very sensitive diagnostic of cluster structure in the core.To resolve a number of problems,including getting the correct slope for the L X−T relation and avoiding exces-sive mass deposition rates for low luminosity clusters,self-similarity of clusters has to be broken.In our model this is achieved byﬂattening the gas density proﬁles of the smaller clusters,which occurs naturally when we include heating of intracluster gas due to the retention of energy from super-novae in all previous collapse stages.Weﬁnd that the energy required agrees well with the supernova energy released in producing the observed metallicities if most of this energy is retained in the intracluster gas.The result is that the above problems are simultaneously resolved once supernova heating is included.We have highlighted the importance of the mass de-position rate and the˙M function as diagnostics of cluster structure.The value of˙M probes the gas density proﬁle at smaller radii than L X and hence is able to give us indepen-dent information.Due to the sensitivity of quantities such as L X and˙M to the structure and density of the hot gas, and the steep slopes of the three distribution functions we consider,detailed gas processes can be as important as cos-mological considerations in determining what we observe.ACKNOWLEDGEMENTSWe thank Stefano Ettori for the results of surface brightness proﬁleﬁts,Clovis Peres for the new calculation of the˙M function,and Vince Eke,Stefano,Clovis and Martin Rees for very helpful discussions.KKSW is grateful to the Croucher Foundation forﬁnancial support.ACF thanks the Royal So-ciety for support.PEJN gratefully acknowledges the hospi-tality of the Institute of Astronomy during part of this work. REFERENCESAllen S.W.,Fabian A.C.,1998,MNRAS,297,L63Baugh C.M.,Cole S.,Frenk C.S.,Lacey C.G.,1998,ApJ,498, 504Bower R.G.,1997,MNRAS,288,355Buote D.A.,Tsai J.C.,1996,ApJ,458,27Cole S.,Ar´a gon-Salamanca A.,Frenk C.S.,Navarro J.F.,Zepf S.E.,1994,MNRAS,271,781Cole S.,Kaiser N.,1988,MNRAS,233,637David L.P.,Jones C.,Forman W.,1995,ApJ,445,578David L.P.,Slyz A.,Jones C.,Forman W.,Vrtilek S.D.,1993, ApJ,412,479Ebeling H.,Edge A.C.,Fabian A.C.,Allen S.W.,CrawfordC.S.,1997,ApJ,479,L101Edge A.C.,Stewart G.C.,Fabian A.C.,1992,MNRAS,258,177 Edge A.C.,Stewart G.C.,Fabian A.C.,Arnaud K.A.,1990, MNRAS,245,559Eke V.R.,Cole S.,Frenk C.S.,Henry J.P.,1998,MNRAS, submitted(astro-ph/9802350)Ettori S.,Fabian A.C.,1998,MNRAS,submittedEvrard A.E.,1997,MNRAS,292,289Evrard A.E.,Henry J.P.,1991,ApJ,383,95Fukazawa Y.,Makishima K.,Tamura T.,Ezawa H.,Xu H.,Ikebe Y.,Kikuchi K.,Ohashi T.,1998,PASJ,50,187Heyl J.S.,Cole S.,Frenk C.S.,Navarro J.F.,1995,MNRAS, 274,755Jones L.R.,Scharf C.,Ebeling H.,Perlman E.,Wegner G., Malkan M.,Horner D.,1998,ApJ,495,100Kaiser N.,1986,MNRAS,222,323Kaiser N.,1991,ApJ,383,104Katz N.,White S.D.M.,1993,ApJ,412,455Kauﬀmann G.,Charlot S.,1998,MNRAS,294,705Kauﬀmann G.,White S.D.M.,Guiderdoni B.,1993,MNRAS, 264,201Kitayama T.,Suto Y.,1996,ApJ,469,480Makino N.,Sasaki S.,Suto Y.,1997,ApJ,497,555Metzler C.A.,Evrard A.E.,1994,ApJ,437,564Mushotzky R.,Loewenstein M.,Arnaud K. A.,Tamura T., Fukazawa Y.,Matsushita K.,Kikuchi K.,Hatsukade I.,1996, ApJ,466,686Nagataki S.,Sato K.,1998,ApJ,in press(astro-ph/9807022) Navarro J.F.,Frenk C.S.,White S.D.M.,1995,MNRAS,275, 720Navarro J.F.,Frenk C.S.,White S.D.M.,1997,ApJ,490,493 (NFW97)Nulsen P.E.J.,Fabian A.C.,1995,MNRAS,277,561(NF95) Nulsen P.E.J.,Fabian A.C.,1997,MNRAS,291,425(NF97) Peres C. B.,Fabian A. C.,Edge A. C.,Allen S.W.,John-stone R.M.,White D.A.,1998,MNRAS,in press(astro-ph/9805122)Spitzer L.,1978,Physical Processes in the Interstellar Medium.Wiley-Interscience,New YorkWhite D.A.,Fabian A.C.,1995,MNRAS,273,72White D.A.,Jones C.,Forman W.,1997,MNRAS,292,419 White S.D.M.,Navarro J.F.,Evrard A.E.,Frenk C.S.,1993, Nature,366,429c 0000RAS,MNRAS000,000–000。

SupernovaeTheexplosioninabubble（超新星泡沫中的爆炸）

[Ontology]Physical sciences / Astronomy and planetary science / Astronomy and astrophysics / Stars [URI /639/33/34/867]Physical sciences / Astronomy and planetary science / Astronomy and astrophysics / High-energy astrophysics [URI /639/33/34/864][Subject strapline]Supernovae[Title]The supernova in a bubble[Standfirst: 230 characters including spaces]The story behind the supernova remnant RCW 86 might be one of the most wondrous ever told.[Author]Peter NugentAstronomers have long sought the progenitor systems of supernovae, since such discoveries provide the only direct checks of our understanding of the death throes of stellar evolution. Much of the work in this field over the past decade and a half has focused its attention on serendipitous pre-explosion imaging garnered by ground and space-based observations of nearby galaxies. With these data, astronomers have been able to place stringent constraints on the progenitor masses of a variety of hydrogen-rich Type II core-collapse supernovae (cc-SNe), upper limits on the mass of several more stripped-mass Type Ib/c supernovae as well as excellent upper limits on the companion stars for a couple of nearby Type Ia supernovae (1,2). Furthermore, in just the past few years, high-cadence optical surveys have provided several supernova discoveries within hours of their explosion. This has allowed astronomers a brief window (often less than 24 hours) to see the effects of the supernova explosion’s shock-breakout on the surrounding environment before the rapidly-expanding ejecta completely overrun it. From such observations links have now been made between Wolf-Rayet-like winds and cc-SNe whose progenitors have suffered significant mass loss (3). These early observations have also been used to detect the potential signature of the ejecta of a thermonuclear (Type Ia) supernova slamming into, and shocking, its binary companion star (4).Writing in Nature Astronomy, Vasilii Gvaramadze and collaborators tackle this problem from the other direction, not by looking at what happened before or during the supernova explosion, but rather at what was left behind hundreds of years later in the supernova’s remnant. They have turned their attention to the supernova remnant RCW 86, located over 8,000 light years away and found between the constellations of Circinus and Centaurus. RCW 86 has had a long and rather convoluted history, with claims of it being the result of both a thermonuclear andcore-collapse supernova. Associations with 10 nearby massive B-type stars, alongwith the fact that the supernova exploded into a “cavity”, perhaps through a massive star’s wind prior to explosion, favour the core-collapse progenitor (5). Recentstudies focused on the X-ray and IR observations of the remnant, showing high iron abundances and strong hydrogen emission from non-radiative shocks, favour the thermonuclear origin (6). There is also a tentative association with the supernova seen by Chinese astronomers in 185 AD (SN 185).What Gvaramadze et al. have added to the story is the detection of a solar-type star strongly polluted with calcium and iron among other elements. It is coincident with a candidate neutron star (NS) within the remnant RCW 86 (see Figure). Moreover, from radial velocity measurements, the G star is in a binary system. This is suggestive of a massive star going supernova, leaving behind a NS and the supernova ejecta polluting a companion. The G star/NS binary is offset from the centre of the RCW 86 remnant, in its own, smaller bubble. They believe that the supernova progenitor was a massive, moving star, which exploded near the edge of its wind bubble and lost most of its initial mass due to common-envelope evolution with this G star. It is a two-step process to manufacture this remnant: the first requiring mass loss during the main-sequence phase creating a large-scale bubble in the interstellar medium, and a second mass loss episode during the red supergiant phase producing a slow, dense wind creating a bow-shock-like structure at the edge of the bubble. They further posit that due to the factor of 6 enhancement of calcium in the G star’s spectrum, that perhaps this supernova is related to the rare calcium-rich subclass. Ca-rich supernovae are a recently identified class of explosions, which are relatively faint at peak and whose brightness drops rapidly. After a few months their spectra are dominated by calcium in emission – hence the moniker. The origins of these supernovae are up for debate. By and large they are associated with early-type galaxies, many of which show signs of recent merger activity, and are often separated by scores of kiloparsecs from the putative host (7). Proposed progenitor scenarios include the merger of a NS and a white dwarf (WD), WD-WD mergers and sub-Chandrasekhar thermonuclear explosions (8,9). Yet this link to Ca-rich supernovae is a bit murky as there are likely viable cc-SNe that could produce the observed abundances given their uncertainties. Overall the argument of Gvaramadze and collaborators is not completely convincing since much of it rests on the unlikely finding of such an odd G star next to a potential neutron star – but it is possible, and it is quite tantalizing.While some may see this work as just adding to the pantheon of potential progenitors for this system, a smoking gun can, and likely will, be found in the next few years that could settle this debate once and for all. It will come to us through an indirect path in the form of a light echo. Just as sound can reflect off the face of a cliff, the light from a nearby supernova can reflect off a sheet of cosmic dust. And if the dust is situated several hundred light years away from the explosion, the light echo itself will be delayed by hundreds of years before it reaches us – giving us the opportunity to see the explosion as it happened – a cosmic DVR. With the advent ofwide-field optical surveys, several of these light echoes have been discovered in thepast few decades. Coupled with 8–10m-class telescopes, spectra of the echoes have been taken that reveal the underlying supernova subclass and, if there are echoescoming from a number of different directions, the three-dimensional nature of the supernova explosion itself (10). Such a discovery for RCW 86 would go a long way to clearing up this mystery and determining if this thermonuclear supernova bubble will burst.Peter Nugent is in the Computational Research Division of the Lawrence Berkeley National Laboratory, M.S. 50B-4206, 1 Cyclotron Road, Berkeley, Calfornia 94720-8139, USA.email:****************References:1. Smartt, S. J. Pub. Astron. Soc. Austrailia. 32, 16-38 (2015).2. Li, W. et al. Nature 480, 348-350 (2011).3. Gal-Yam, A. et al. Nature 509, 471-474 (2014).4. Cao, Y. et al. Nature 521, 328-331 (2015).5. Vink, J. et al. Astron. Astrophys. 328, 628-633 (1997).6. Williams, B. J. et al. Astrophys J. 741, 96-111 (2011).7. Foley, R. J. Mon. Not. R. Astron. Soc. 452, 2463-2478 (2015).8. Lyman, J. D. et al. Mon. Not. R. Astron. Soc. 444, 2157-2166 (2014).9. Sullivan, M. et al. Astrophys J. 732, 118-131 (2011).10. Rest, A. & Welch, D. L. Pub. Astron. Soc. Austrailia. 29, 466-481 (2012).Figure 1 | Title. Text.。

The Brightest Star

The Brightest StarSupernovae refers to the violent explosion of massive stars in the late period of evolution or of some binary systems in the middle of its evolution process. The explosion is so powerful that the radiation it emits can illuminate the entire galaxy （at the brightest of supernovae，its luminosity is 1 billion times higher than that of the sun）and it is also the most powerful explosion second to the Big Bang from which the universe was born. Therefore，at the beginning of its appearance，it has gained lots of attention of the world. In ancient China it was called Ke Sing （guest star）. Next，more secrets of supernovae will continue to be told.Members of the Supernova FamilyAccording to spectroscopic analysis，astronomers have found some universalities in the absorption line in the supernova spectra，so that it’s possible to classify supernovae. Simply speaking，the first level of classification is based on the existence of a hydrogen element （H）absorption spectrum in the spectra. If there is no hydrogen，then it is classified as type I supernova，and if hydrogen exists，then it is a type IIsupernova. In addition，it was observed that there arehyper-bright supernovae and mutated supernovae.Type I supernovae can also be further divided according to other spectra：A typical type I a supernova has a strong absorption line of silicon at 615 nm，and if the absorption line of the silicon element is not conspicuous or strong enough，it is then categorized as an type I b or I c supernova. Normal type II supernovae can be divided into two kinds，II-P and II-L. The curve of luminosity of II-P supernovae variating with time has an obvious "platform" period，while that of II-L supernovae seems to be linearly attenuating.The Formation of SupernovaStudies have shown that the mechanism of I a supernova formation is：after a white dwarf mainly consisting of carbon-oxygen absorbs enough material from the companion star and reaches the upper limit of the mass （i.e.，the Chandrasekhar limit，about 1.4 times of the mass of the sun），its electron degeneracy is not strong enough to counteract its own gravitational force，resulting in an overall collapse，and finally through a series of complex processes an uncontrolled comminuted explosions takes place，forming a type I a supernova explosion. Due to Chandrasekhar mass limits，thetype I a Supernova explosion has a standard luminosity.Type II supernova is by its nature a catastrophic explosion of massive stars caused by internal collapses. Its strong gravitational force causes the star to have an intense collapsing.A neutron star comes into being if it collapses into a dense body with a diameter of a bit more than 10 kilometers mainly composed of neutrons，of which the neutron degeneracy pressure is sufficient to counteract gravity. If the neutron degeneracy pressure is still too weak to counteract the gravity，the star will eventually turn out to be a black hole. At the moment of the formation of a neutron star or a black hole，the violently released energy and the largely ejected mass make the supernova explosion to occur. Since the massive stars are different in terms of their mass respectively，the luminosity of the supernova explosion they release is also different from each other，so that the luminosity has no standard value. When a supernova explodes，a huge amount of high-energy radiation is released，which will undoubtedly destroy any life form nearby. Fortunately，according to observation，most of the massive stars are far from the solar system，and there is no sign of explosion of nearer ones. Life on earth will not be threatened by supernovae for the time being. How to ObserveSupernovaIt is estimated that in galaxies of the similar size of the Milky Way，the probability of a supernova explosion is approximately one or two times every 100 years，so waiting for the next supernova explosion to happen in the Milky Way is just a waste of time. There are hundreds of millions of galaxies in the observable universe，so it’s very likely that a supernova outside the Milky Way is found. Further testification can be made through continuous searching and monitoring of the starlit sky to find "transient body" that suddenly flickers brightly. In the summer of 2015，Chinese scientists observed a supernova explosion 3.8 billion light-years away from the Indus. It is by far the brightest supernova observed，of which the highest luminosity is 570 billion times stronger than that of the sun，about 20 times of the total luminosity of hundreds of billions of stars of the entire Milky Way galaxy. It’s hundreds of times more brighter than a normal supernova，considered as superbright supernova.What is left after the supernova explosion is known as a supernova remnant. According to records，at least 8 supernovae have appeared in the Galaxy in more than 2000 years，the most famous of which is the "Tian Guan Ke Sing" （Guest Star in theskyline），of which a detailed script was kept in the Chinese Song Dynasty （1054）. It left a spectacular crab-like nebula （M1）after its explosion. The last recorded supernova in the Milky Way is the Kepler supernova that exploded in 1604.Knowledge Link：The Significance of Supernova ExplosionAny of the heavier elements in nature，such as calcium in bone，iron in blood，gold in jewelry，and uranium for nuclear power plants，are all produced and released into space by internal nuclear fusion of stars or supernova explosions，which means supernovae can produce abundant heavy elements for our universe. Meanwhile，by compressing nearby nebulae，the shock waves caused by supernova explosions can enable the formation of new stars （and planets）. It is never too much to say that human wouldn’t exist without supernova.。

天文摄影展英语作文范文

天文摄影展英语作文范文英文回答：Astronomy photography captures the beauty and wonder of the cosmos, allowing us to appreciate the vastness and complexity of our universe. Through the lens of a camera, astronomers and enthusiasts alike can capture stunning images of distant galaxies, nebulae, and other celestial objects, revealing the hidden wonders of the night sky.One of the most captivating aspects of astronomy photography is its ability to transport viewers to distant realms. By capturing the faint glow of distant stars and galaxies, astrophotographers can transport us to the far reaches of the universe, offering a glimpse into the unknown. The resulting images evoke a sense of awe and wonder, reminding us of our place in the vast cosmic tapestry.Beyond its aesthetic appeal, astronomy photography alsoserves as a valuable tool for scientific research. By studying the light emitted by celestial objects, astronomers can gather crucial data on their composition, distance, and motion. Astrophotography has played a pivotal role in advancing our understanding of the universe,helping astronomers to unravel the mysteries of black holes, supernovae, and other cosmic phenomena.To capture stunning astronomy photographs, enthusiasts employ specialized equipment and techniques. Wide-field lenses allow photographers to capture vast areas of the sky, showcasing the intricate patterns of stars and constellations. Telephoto lenses, on the other hand, enable photographers to zoom in on specific celestial objects, revealing their intricate details and textures. In addition, specialized filters can enhance the contrast and clarity of astrophotographs, bringing out the subtle colors andfeatures of celestial objects.Patience and perseverance are essential qualities for successful astronomy photography. Astrophotographers often spend hours or even nights outdoors, waiting for theperfect conditions to capture their desired images. The rewards for their dedication, however, are immeasurable. Through the lens of a camera, astronomy photography unveils the beauty and wonders of the cosmos, inspiring a sense of awe and curiosity in all who gaze upon its images.中文回答：天文摄影展示了宇宙的美丽和奇观，让我们欣赏到我们宇宙的浩瀚和复杂性。

蟹状星云是什么英语作文

蟹状星云是什么英语作文In the vast and mysterious universe, there exists a remarkable celestial object known as the Crab Nebula.The Crab Nebula is a fascinating and distinctive structure that holds great importance in astronomy.It is a massive cloud of gas and dust located in a specific region of the universe.The Crab Nebula gets its name due to its resemblance to a crab, as observed through telescopes.This nebulosity is formed as a result of a spectacular supernova explosion.A supernova is a powerful event that occurs when a massive star reaches the end of its life.The energy released during this explosion gives rise to the formation of the Crab Nebula.The nebula is filled with incredibly hot gas and emits various forms of radiation.It is a source of intense light and provides astronomers with valuable information.Studying the Crab Nebula helps us understand several aspects of the universe.It offers insights into the processes of star formation and evolution.It also allows us to investigate the properties and behavior of gas and dust in space.The Crab Nebula is not only of scientific significance but also a visually stunning sight.Observing it through telescopes reveals its intricate details and beauty.。

关于宇宙的英语作文

关于宇宙的英语作文The Universe。

The universe is a vast and mysterious place that has captivated human beings for centuries. It is a topic that has sparked countless questions and theories, and continues to baffle scientists and astronomers to this day. In this essay, I will explore some of the key aspects of the universe and attempt to shed light on its many enigmas.One of the most fundamental questions about the universe is its origin. How did it come into existence? The prevailing scientific theory is the Big Bang theory, which suggests that the universe began as a singularity, a point of infinite density and temperature. Approximately 13.8 billion years ago, this singularity exploded, giving rise to the expansion of space and the formation of matter and energy. While this theory provides a plausible explanation for the origin of the universe, there are still many unanswered questions about what triggered the Big Bang andwhat existed before it.The universe is composed of billions of galaxies, each containing billions of stars. Our own galaxy, the Milky Way, is just one of many in the vast expanse of space. Within these galaxies, stars are born, live out their lives, and eventually die. The life cycle of a star depends on its mass. Smaller stars, like our sun, will eventually exhaust their nuclear fuel and become white dwarfs. Larger stars,on the other hand, will undergo a supernova explosion, leaving behind a dense core known as a neutron star or possibly even collapsing into a black hole.Black holes are one of the most intriguing objects in the universe. They are regions of space where gravity is so strong that nothing, not even light, can escape its grasp. They form when a massive star collapses under its own gravity, creating a singularity with infinite density.Black holes have a profound effect on their surroundings, distorting space and time and devouring anything that comes too close. While they are fascinating to study, much about black holes remains a mystery, including what happensbeyond the event horizon and how they might be connected to the fabric of space-time.The universe is also home to various celestial bodies, such as planets, moons, asteroids, and comets. Our own solar system is just a small part of the universe, consisting of the sun, eight planets, and numerous smaller objects. The search for extraterrestrial life has long been a topic of interest, and recent discoveries have shown that there may be habitable conditions on other planets or moons within our own solar system. However, the vastness of the universe suggests that there could be countless other planets with the potential for life, waiting to be discovered.In conclusion, the universe is a complex and awe-inspiring entity that continues to fascinate and challenge us. From its mysterious origins to the existence of black holes and the possibility of extraterrestrial life, there are still many unanswered questions about the universe. As we continue to explore and study the cosmos, we may comecloser to unraveling its secrets and gaining a deeper understanding of our place in the universe.。

追寻宇宙中的第一缕阳光作文

追寻宇宙中的第一缕阳光作文英文回答：As I set out to chase the first ray of sunlight in the universe, I couldn't help but feel a sense of excitement and wonder. The idea of witnessing something so ancient and powerful filled me with a sense of awe.I started my journey by researching the origins of the universe and the formation of stars. I learned that thefirst stars in the universe were formed around 100 million years after the Big Bang. These stars were massive and short-lived, but they played a crucial role in shaping the universe as we know it today.I traveled to different observatories and spoke to astronomers and astrophysicists to gather more information about the early universe. They explained to me how thefirst stars were formed from the primordial gases left over from the Big Bang, and how they eventually exploded insupernovae, scattering heavy elements into space.After months of preparation and anticipation, I finally embarked on my journey to find the first ray of sunlight in the universe. I traveled to remote locations with clearskies and minimal light pollution, hoping to catch aglimpse of the cosmic dawn.One night, as I gazed up at the starry sky, I saw afaint glow on the horizon. It was the first light of a new day, and I knew that I was witnessing something truly special. The feeling of awe and wonder that washed over mein that moment is something I will never forget.中文回答：当我踏上寻找宇宙中第一缕阳光的旅程时，我感到兴奋和好奇。

无与伦比的星空作文英语

无与伦比的星空作文英语Title: The Unparalleled Starry Sky。

As night falls and the darkness blankets the earth, a magnificent spectacle unfolds above – the unparalleled starry sky. With its vastness and beauty, it captivates hearts and ignites the imagination of all who behold it.Gazing up at the celestial canvas, one is drawn into a realm of wonder and awe. Countless stars twinkle like precious jewels scattered across the heavens, each one a distant sun with its own story to tell. The constellations, ancient patterns etched by the human imagination, weavetales of heroes, gods, and mythical creatures across the velvety expanse.In the depths of space, beyond the reach of earthly worries and troubles, lies a sense of boundless possibility. The sheer scale of the universe stretches the limits of comprehension, reminding us of our place in the grandtapestry of existence. It is humbling yet exhilarating to contemplate the vastness of creation, to ponder the mysteries that lie beyond our grasp.The starry sky also serves as a timeless beacon of guidance and inspiration. For millennia, navigators have relied on the positions of the stars to chart their course across the seas, guiding them safely to distant shores. In the quiet solitude of the night, poets and dreamers have found solace and inspiration in the gentle glow of distant suns, their light whispering secrets of the cosmos.But perhaps the most profound impact of the starry sky is its ability to evoke a sense of wonder and curiosity in the hearts of humanity. From the earliest civilizations to the present day, humans have looked to the stars with a mixture of reverence and fascination, seeking to unlock the secrets of the universe and understand our place within it.In today's world, where artificial lights often obscure the brilliance of the night sky, it is more important than ever to preserve and protect this natural wonder. Byreducing light pollution and promoting conservation efforts, we can ensure that future generations will continue to be awed and inspired by the unparalleled beauty of the starry sky.In conclusion, the starry sky stands as a timeless symbol of beauty, wonder, and exploration. Its vastness and complexity remind us of the boundless mysteries that lie beyond our comprehension, while its beauty inspires us to reach for the stars and strive for greatness. In a world filled with chaos and uncertainty, the starry sky remains a source of solace and inspiration, a beacon of hope shining brightly in the darkness of the night.。

高中物理：将闪电冻结起来

将闪电冻结起来原文地址：/chapter-six/trap-lightning-in-a-block/。

用亚克力板、墨粉冻结闪电，显示电荷流动的路径。

在俄亥俄州的牛顿瀑布，有许多不同寻常的值得一看的东西。

那里的沃尔玛超市有为马车准备的拴马桩，军事基地的直升机和坦克骄傲地排列在小山上……但是我到这里却是为了所有事情中最为不同寻常的事：当地的高频高压加速器（Dynamitrons）。

我到这里来的目的是为了冻结闪电。

肯特州立大学的NEO高频高压加速器有4层楼高，电压高达500万伏。

这是一个很像电视机显像管的粒子加速器，只是更大。

（所以可以认为电视机的显像管是个家用粒子加速器。

）这个加速器和电视机显像管都是利用很高的电压和磁场将电子轰向目标。

在电视机中，目标是荧光屏；而在加速器中，它通常是被射线硬化的塑料管件。

但是，我参加的那个由退休电机工程师伯特·希克曼、物理学家比尔·哈撒韦和金·戈因斯组成的团队的工作结果是利希贝格图形（Lichtenberg Figures）——在清澈的亚克力中永久冻结的闪电。

我们租用了NEO加速器一天的时间，当把它调节到大约300万伏时，它迸发出的高能电子穿过了亚克力表面深入其内部。

由于这种塑料是很好的绝缘体，所以它可以将电子囚禁在里面。

在从机器上卸下来之后，那些塑料块看起来没有任何异样，但是它们就像黄蜂的巢穴一样，里面充满了拼命想逃走的电子。

如果将它们静静地放置在那里，这些电子可以被囚禁几个小时而不会跑掉，但如果用钉子去敲击塑料块，就会为电子打开一条通道，使它们迅速逃走。

这些电子从塑料块的各个部分汇集到了被钉子敲击的那一点，在途中形越来越大的电流。

在这些电子逃离的过程中会产生热量，使塑料内部产生损伤，从而永久地留下电子“逃跑”的路径，即枝杈状的足迹。

如果在一道闪电迸发之前你能看到一朵雷雨云内部1纳秒时间里发生的事情，你就可以看到同一类图形。

闪电是不会一下子突然形成的，它必须把云朵各个部分的电荷汇集起来。

天文英语名词

天文英语名词The cosmos is a vast expanse that has always captivated our imagination. From the celestial bodies that light up the night sky to the mysteries of the universe, astronomy offers a wealth of intriguing terms.Galaxies, for instance, are sprawling collections of stars, gas, and dust, each a universe in itself. The Milky Way, our home galaxy, is a spiraling masterpiece of cosmic beauty, filled with billions of stars.Astronomers use powerful telescopes to peer into the depths of space, observing phenomena like supernovae, the explosive end of a massive star's life cycle. These events release an immense amount of energy, briefly outshining entire galaxies.Black holes are perhaps the most enigmatic of all astronomical objects. Their gravitational pull is so strong that not even light can escape their grasp, making them invisible to direct observation.Comets, on the other hand, are icy visitors from the outer reaches of our solar system. As they approach the sun, their icy cores heat up, creating a glowing tail that can be seen from Earth.The study of the heavens is not just about observing;it's also about understanding the laws that govern the universe. Terms like gravity, orbits, and celestial mechanics help us comprehend the movements of celestial bodies.Astronomy also delves into the origins of the universe itself, with concepts like the Big Bang theory explaining the birth of everything we see today.Planets, moons, and asteroids are all part of the celestial ballet, each with unique characteristics andstories to tell. The exploration of these bodies has led to the discovery of water on Mars and the possibility of life beyond Earth.In the end, the language of astronomy is a bridge between the human desire to understand and the silent, awe-inspiring majesty of the stars above. It's a vocabulary that speaks to our innate curiosity and our place in the cosmos.。