The Intriguing Distribution of Dark Matter in Galaxies

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TED：带你了解宇宙暗物质

TED：带你了解宇宙暗物质TED英语演讲课给心灵放个假吧今天的TED演讲带大家了解宇宙暗物质。

The ancient Greeks had a great idea:古代希腊人有一个伟大的想法：The universe is simple.宇宙是简单的。

In their minds,在他们心中，all you needed to make it were four elements: 要建构宇宙只须要四种元素：earth,土、air,空气、fire,火、and water.还有水。

As theories go, it’s a beautiful one.就像它的理论一样，这是美丽的。

It has simplicity and elegance.既简单、又优雅。

It says that by combining理论中认為the four basic elements in different ways,藉由四种元素的不同组合，you could produce all the wonderful diversity of the universe. 可以產生宇宙万物。

Earth and fire, for example,比如说土加火，give you things that are dry.就会有一些乾的东西。

Air and water, things that are wet.而空气加水，就会得到湿的东西。

But as theories go, it had a problem.但依照这理论，会有一个问题。

It didn’t predict anything that could be measured,它没办法预测出任何可以测量的事物，and measurement is the basis of experimental science.而测量又是实验科学的基础。

Worse still, the theory was wrong.更糟的是，这理论是错的。

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.。

宇宙的奥秘作文英文

宇宙的奥秘作文英文英文：The mysteries of the universe have always fascinated me. As a human being, it is natural for me to wonder about the vastness of space and the secrets it holds. Throughout history, scientists and philosophers have tried to unravel the mysteries of the universe, but there is still so muchwe don't know.One of the biggest mysteries of the universe is dark matter. Scientists have observed that the gravitationalpull of visible matter in the universe is not strong enough to hold galaxies together. This led them to hypothesize the existence of dark matter, a type of matter that does not interact with light or other forms of electromagnetic radiation. Although we can't see dark matter directly, we can observe its effects on visible matter.Another mystery of the universe is the nature of blackholes. These are regions in space where the gravitational pull is so strong that nothing, not even light, can escape. Black holes are formed when massive stars collapse in on themselves, but scientists still don't fully understand what happens inside a black hole. Some theories suggestthat black holes could be portals to other dimensions or even other universes.Despite our limited knowledge, human beings have made incredible discoveries about the universe. For example, the discovery of exoplanets, planets that orbit stars outside of our solar system, has opened up new possibilities for the search for extraterrestrial life. The study of cosmic microwave background radiation has given us insights into the early universe and the Big Bang.In conclusion, the mysteries of the universe are vast and complex. As humans, it is natural for us to be curious about the unknown. While we may never fully understand the secrets of the universe, our quest for knowledge will continue to push the boundaries of what we know.中文：宇宙的奥秘一直吸引着我。

黑洞介绍英语作文初一

黑洞介绍英语作文初一Title: Exploring the Mysteries of Black Holes。

Black holes are fascinating objects in the universethat have captured the imagination of scientists and the public alike. These enigmatic entities are characterized by their immense gravitational pull, which is so strong that nothing, not even light, can escape from them. In this essay, we will delve into the intriguing world of black holes and explore their properties, formation, and significance in astrophysics.To begin with, let's discuss the nature of black holes.A black hole is formed when a massive star collapses under its own gravity at the end of its life cycle. As the star's core runs out of nuclear fuel, it can no longer support its own weight, leading to a catastrophic collapse. This collapse causes the star to shrink to a point of infinite density called a singularity, surrounded by an event horizon, which marks the boundary beyond which nothing canescape.The concept of the event horizon is crucial to understanding the behavior of black holes. It represents the point of no return, beyond which the gravitational pull is so strong that even light cannot break free. This phenomenon makes black holes invisible to direct observation, as they do not emit any light themselves. Instead, scientists infer their presence through theeffects they have on surrounding matter and light.Despite their invisibility, black holes can have a profound impact on their surroundings. For example, when matter gets too close to a black hole, it is drawn into a swirling disk of gas and dust called an accretion disk. The intense friction and gravitational forces within the accretion disk cause it to heat up and emit high-energy radiation, such as X-rays, which can be detected by telescopes.Another fascinating aspect of black holes is their role in the evolution of galaxies. Supermassive black holes,which can contain the mass of millions or even billions of suns, are thought to reside at the centers of most galaxies, including our own Milky Way. These behemoths exert a powerful influence on their host galaxies, regulating the formation of stars and influencing the dynamics of galactic structures.In recent years, scientists have made significantstrides in our understanding of black holes, thanks to advances in observational techniques and theoretical modeling. For example, the Event Horizon Telescope collaboration made headlines in 2019 with the first-ever image of a black hole's silhouette, providing direct evidence of their existence.Moreover, theoretical frameworks such as Einstein's theory of general relativity have provided a mathematical description of black holes' behavior, allowing scientiststo make predictions and test them against observational data. However, many mysteries surrounding black holes remain, such as the nature of the singularity at their core and the possibility of wormholes connecting distant regionsof space-time.In conclusion, black holes are among the mostintriguing phenomena in the universe, challenging our understanding of physics and the nature of reality itself. While much progress has been made in unraveling their mysteries, there is still much we have yet to learn about these enigmatic objects. Continued research and exploration are essential if we are to unlock the secrets of black holes and expand our knowledge of the cosmos.。

《探索宇宙的奥秘》高中生英语作文

《探索宇宙的奥秘》高中生英语作文Exploring the Mysteries of the UniverseThe universe, with its vast expanse of space, celestial bodies, and numerous mysteries, has always captivated the human imagination.From ancient times, humans have gazed up at the stars, planets, and constellations in awe and curiosity, attempting to unravel the enigmas that lie beyond our planet Earth.One of the most fascinating aspects of exploring the universe is the study of black holes.These incredibly dense regions of space have a gravitational pull so strong that not even light can escape from them.The concept of black holes was once considered purely theoretical, but thanks to advancements in technology and the work of brilliant scientists, we now have evidence of their existence.The Hubble Space Telescope has provided us with stunning images of black holes, allowing us to better understand these enigmatic phenomena.Another area of interest in the universe is the study of exoplanets, or planets outside our solar system.With the help of powerful telescopes and space probes, scientists have discovered thousands of exoplanets orbiting distant stars.Some of these planets resemble Earth, with conditions that could potentially support life.The discovery of exoplanets has led to exciting possibilities of finding alien life forms and has sparked our desire to explore and colonize other planets.The formation and evolution of the universe itself are also topics of intense research.Cosmologists study the Big Bang Theory, which posits that the universe began as a singularity and has been expanding ever since.By analyzing the cosmic microwave background radiation and the distribution of galaxies, scientists can piece together the history of the universe and gain insights into its ultimate fate.In addition to these mysteries, the concept of dark matter and dark energy poses a significant challenge to our understanding of the universe.These mysterious components make up the majority of the universe's mass and energy, yet they have never been directly observed.The search for dark matter and dark energy is ongoing, and scientists hope to uncover their nature and understand their role in the universe.As we continue to explore the universe, we are reminded of the limitations of human knowledge.The mysteries that lie beyond our planet Earth push us to question, discover, and learn.Whether we find alien life, solve the riddles of dark matter, or unravel the secrets of black holes, the exploration of the universe will undoubtedly continue to inspire and challenge us.It is through this exploration that we expand our understanding of the cosmos and our place within it.。

黑洞介绍英语作文带翻译

黑洞介绍英语作文带翻译Title: Exploring the Enigma of Black Holes。

Black holes are among the most intriguing and enigmatic phenomena in the universe. Formed from the collapse of massive stars, these cosmic entities possess gravitational forces so strong that even light cannot escape their grasp. In this essay, we delve into the mysteries of black holes, exploring their formation, properties, and the profound impact they have on our understanding of the universe.黑洞是宇宙中最引人入胜和神秘的现象之一。

这些天体是由大质量恒星的坍缩形成的，它们具有如此强大的引力，以至于连光都无法逃脱它们的吸引。

在本文中，我们深入探讨黑洞的形成、特性以及它们对我们对宇宙的理解产生的深远影响。

Formation of Black Holes。

Black holes originate from the remnants of massive stars that have exhausted their nuclear fuel and undergogravitational collapse. When a massive star reaches the end of its life cycle, it can no longer sustain nuclear fusion reactions to counteract the inward pull of gravity. Consequently, the star's core collapses under its own weight, leading to the formation of a black hole.黑洞起源于已经耗尽核燃料并且发生引力坍缩的大质量恒星的残骸。

关于宇宙的英语作文

关于宇宙的英语作文The Universe: A Mysterious and Vast Realm。

The universe, a vast and mysterious realm, has captivated human curiosity for centuries. It is a subject that has been explored by scientists, philosophers, and astronomers alike. In this essay, I will delve into various aspects of the universe, including its origins, its composition, and the possibility of extraterrestrial life.To begin with, the universe is believed to have originated from a single point known as the Big Bang. According to this theory, approximately 13.8 billion years ago, all matter and energy were compressed into an incredibly dense and hot state. Suddenly, this singularity expanded rapidly, resulting in the formation of galaxies, stars, and planets. This event not only gave birth to the universe but also set the stage for the existence of life as we know it.The composition of the universe is predominantly made up of dark matter and dark energy, which together account for about 95% of its total mass-energy. Dark matter, although invisible and undetectable, exerts gravitational forces that influence the motion of visible matter. On the other hand, dark energy is believed to be responsible for the accelerated expansion of the universe. These two mysterious components continue to baffle scientists and prompt further research to understand their nature and impact on the universe.Within the universe, galaxies serve as the building blocks of the cosmic structure. Our own galaxy, the Milky Way, is just one of billions of galaxies scattered throughout the universe. Each galaxy consists of billions or even trillions of stars, surrounded by gas, dust, and other celestial objects. The stars, like our Sun, are born from clouds of gas and dust, and their life cycles play a crucial role in shaping the universe. Some stars end their lives in massive explosions called supernovae, which release heavy elements into space, contributing to the formation of new stars and planets.One of the most intriguing questions regarding the universe is the existence of extraterrestrial life. With billions of galaxies, each containing billions of stars, the possibility of life beyond Earth seems highly likely. Scientists have been actively searching for signs of life on other planets and moons within our own solar system. The discovery of water on Mars and the potential habitability of moons such as Europa and Enceladus have further fueled the excitement of finding extraterrestrial life. However, until concrete evidence is found, the existence of intelligent life beyond Earth remains speculative.In conclusion, the universe is an enigmatic and vast realm that continues to fascinate humanity. From itsorigins in the Big Bang to its composition of dark matter and dark energy, the universe holds many secrets waiting to be unraveled. The exploration of galaxies, stars, and planets provides valuable insights into the evolution of the universe and the potential for extraterrestrial life. As we continue to push the boundaries of scientific knowledge, the universe will undoubtedly reveal more of itswonders, inspiring future generations to delve deeper into its mysteries.。

关于银河系的英语文章

关于银河系的英语文章The Milky Way, our home galaxy, is a vast and mysterious place that has captured the imaginations of scientists and stargazers for centuries. Stretching across 100,000 light-years and containing billions of stars, the Milky Way is a truly awe-inspiring sight in the night sky.At the center of the Milky Way lies a supermassive black hole called Sagittarius A, which has a mass millions of times that of our sun. This black hole exerts a powerful gravitational pull on the stars and other celestial bodies that orbit around it, shaping the structure of the galaxy as a whole.The Milky Way is a spiral galaxy, meaning that it has a flat, disk-like shape with spiral arms extending outwards from a central bulge. These spiral arms are made up of stars, gas, and dust, and they are where most of the star formation in the galaxy occurs. As stars are born and die within these arms, they create the beautiful patterns of light and dark that we see when we look up at the night sky.One of the most fascinating features of the Milky Way is its halo of dark matter, an invisible substance that makes up the majority of the galaxy's mass. Dark matter does not emit, absorb, or reflect light, so it cannot be seen directly, but its presence can be inferred from the way it interacts with visible matter through gravity.The Milky Way is also home to a number of satellite galaxies, including the Large and Small Magellanic Clouds, which orbit around the main galaxy. These smaller galaxies are thought to have been captured by the Milky Way's gravity in the distant past, and they provide valuable insights into the formation and evolution of galaxies in general.In addition to stars and galaxies, the Milky Way is also filled with vast clouds of gas and dust, which are the raw materials from which new stars are born. These clouds of gas and dust can be seen in the form of glowing nebulae, such as the famous Orion Nebula, which is a hotbed of star formation.As we continue to study the Milky Way and unravel its mysteries, we are constantly amazed by the beauty and complexity of our galactic home. From the swirling spiral arms to the invisible dark matter halo, the Milky Way is a testament to the power and wonder of the universe in which we live.。

关于宇宙的英语作文,不少于80字

关于宇宙的英语作文,不少于80字全文共3篇示例，供读者参考篇1The universe is a vast and mysterious place, filled with countless stars, planets, galaxies, and other celestial bodies. Scientists and astronomers have been studying the universe for centuries, trying to unravel its many secrets and understand the origins of the cosmos.One of the most fascinating things about the universe is its sheer size. The observable universe is estimated to be about 93 billion light-years in diameter, containing billions of galaxies, each with billions of stars. The universe is constantly expanding, with galaxies moving away from each other at incredible speeds.Another intriguing aspect of the universe is its age. Scientists believe that the universe is about 13.8 billion years old, dating back to the Big Bang, the event that created the universe as we know it. Since then, the universe has been evolving and changing, giving rise to the many wonders we see in the night sky.One of the biggest mysteries of the universe is the existence of dark matter and dark energy. These are invisible substancesthat make up the majority of the universe's mass and energy, yet their exact nature remains unknown. Scientists are still studying these mysterious forces in the hopes of unlocking their secrets.The universe is also home to many fascinating phenomena, such as black holes, supernovas, and quasars. These powerful events and objects give us a glimpse into the extreme conditions and forces at work in the cosmos.In conclusion, the universe is a vast and wondrous place, full of mysteries waiting to be uncovered. As we continue to explore and study the universe, we will gain a greater understanding of our place in the cosmos and the wonders that surround us.篇2The universe has always fascinated mankind with its vastness, mystery, and beauty. From the twinkling stars in the night sky to the swirling galaxies millions of light-years away, the universe is full of wonders waiting to be discovered.One of the most captivating aspects of the universe is the sheer size of it. Scientists estimate that the observable universe is about 93 billion light-years in diameter, containing billions of galaxies, each with billions of stars. It is impossible for the humanmind to comprehend the vastness of space, and yet we continue to explore and study it in the hopes of unraveling its secrets.Another intriguing aspect of the universe is its mystery. Despite centuries of scientific exploration, there are still many unanswered questions about the nature of the universe. From the existence of dark matter and dark energy to the possibility of other dimensions or parallel universes, the universe is full of enigmas waiting to be solved.But perhaps the most awe-inspiring aspect of the universe is its beauty. From the graceful dance of the planets around the sun to the explosive death of a star in a supernova, the universe is a symphony of color, light, and energy. Whether gazing at the swirling clouds of Jupiter or the delicate rings of Saturn, the universe never fails to inspire wonder and awe in all who behold it.In conclusion, the universe is a vast, mysterious, and beautiful place that will continue to captivate and inspire mankind for generations to come. As we continue to explore and study the cosmos, we are reminded of our place in the universe and the infinite possibilities that lie beyond our wildest imagination.篇3The universe is a vast and mysterious place that has captured the imaginations of humans for centuries. From the twinkling stars in the night sky to the swirling galaxies billions of light years away, the universe is a place of wonder and fascination.One of the most fascinating aspects of the universe is its sheer size. The universe is unimaginably large, with billions of galaxies, each containing billions of stars. The distances between these galaxies are so vast that they can only be measured in light years, the distance that light travels in one year. This vastness is difficult for the human mind to comprehend, but it is a testament to the immense scale of the universe.Another intriguing aspect of the universe is its age. Scientists believe that the universe is approximately 13.8 billion years old, a truly astonishing figure. This age is determined by studying the cosmic microwave background radiation, the afterglow of the Big Bang that created the universe. By studying this radiation, astronomers can learn about the early history of the universe and how it has evolved over time.The universe is also home to a menagerie of exotic and mysterious objects, such as black holes, neutron stars, and darkmatter. Black holes are regions of space where gravity is so strong that nothing, not even light, can escape. Neutron stars are the remnants of massive stars that have exploded in supernovae, leaving behind incredibly dense cores. Dark matter is an enigmatic substance that makes up the majority of the mass in the universe, yet it emits no light and interacts very weakly with ordinary matter.Despite its vastness and complexity, the universe is governed by a set of fundamental physical laws that can be understood and studied by scientists. Through the use of telescopes, satellites, and other observational tools, astronomers are able to explore the universe and uncover its secrets. By studying the light emitted by distant objects, astronomers can learn about the composition, temperature, and motion of stars and galaxies. By observing the effects of gravity on matter, astronomers can infer the presence of dark matter and black holes. And by analyzing the cosmic microwave background radiation, astronomers can learn about the origins of the universe and how it has evolved over time.In conclusion, the universe is a vast and fascinating place that has intrigued humans for centuries. From its immense size and age to its exotic objects and mysterious properties, theuniverse is a treasure trove of knowledge waiting to be explored. By studying the universe and uncovering its secrets, we can gain a deeper understanding of our place in the cosmos and the nature of the universe itself.。

科学冷知识科普

科学冷知识科普Science is full of fascinating and little-known facts that can pique our curiosity and expand our understanding of the world around us. For example, did you know that the average human body contains enough iron to make a small nail, or that a single bolt of lightning carries enough energy to toast 100,000 slices of bread? These intriguing pieces of information not only make us marvel at the wonders of nature, but also inspire us to delve deeper into the mysteries of science.科学充满了引人入胜且鲜为人知的事实，这些事实不仅可以激发我们的好奇心，还可以扩展我们对周围世界的理解。

例如，你知道吗，人体平均含有足够的铁量制作一根小钉吗？又或者，一道闪电所携带的能量足以烤熟10万片面包。

这些引人入胜的信息不仅让我们对自然的奇迹感到惊叹，还激励我们深入探索科学的奥秘。

One of the most mind-boggling aspects of science is the concept of quantum entanglement, where two particles become connected in such a way that the state of one particle instantly affects the state of the other, regardless of the distance between them. Thisphenomenon, predicted by quantum mechanics, challenges our traditional notions of cause and effect and raises profound questions about the nature of reality. Despite being a complex and mysterious phenomenon, quantum entanglement has been experimentally verified and plays a crucial role in the development of quantum technologies.科学中最令人费解的一个方面是量子纠缠的概念，其中两个粒子以一种连接的方式变得相互关联，以至于其中一个粒子的状态立即影响到另一个粒子的状态，而不管它们之间的距离有多远。

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arXiv:astro-ph/0203457v1 26 Mar 2002TheIntriguingDistributionofDarkMatterinGalaxies

PaoloSalucci1andAnnamariaBorriello1(1)InternationalSchoolforAdvancedStudiesSISSA-ISAS–Trieste,I

Abstract.Wereviewthemostrecentevidencefortheamazingpropertiesofthedensitydistributionofthedarkmatteraroundspiralgalaxies.Theirrotationcurves,coaddedaccordingtothegalaxyluminosity,conformtoanUniversalproﬁlewhichcanberepresentedasthesumofanexponentialthindisktermplusasphericalhalotermwithaﬂatdensitycore.Fromdwarfstogiants,thesehalosfeatureaconstantdensityregionofsizer0andcoredensityρ0relatedbyρ0=4.5×10−2(r0/kpc)−2/3M⊙pc−3.Atthehighestmassesρ0decreasesexponentiallywithr0,revealingalackofobjectswithdiskmasses>1011M⊙andcentraldensities>1.5×10−2(r0/kpc)−3M⊙pc−3

implyingamaximummassof≈2×1012M⊙foradarkhalohostingastellardisk.Theﬁnestructureofdarkmatterhalosisobtainedfromthekinematicsofanumberofsuitablelow–luminositydiskgalaxies.Thehalocircularvelocityincreaseslinearlywithradiusouttotheedgeofthestellardisk,implyingaconstantdarkhalodensityovertheentirediskregion.ThepropertiesofhalosaroundnormalspiralsprovidesubstantialevidenceofadiscrepancybetweenthemassdistributionspredictedintheColdDarkMatterscenarioandthoseactuallydetectedaroundgalaxies.

1IntroductionRotationcurves(RC’s)ofdiskgalaxiesarethebestprobefordarkmatter(DM)ongalacticscale.Notwithstandingtheimpressiveamountofknowledgegatheredinthepast20years,onlyveryrecentlywestarttoshedlighttocrucialaspectsofthemassdistributionofdarkhalos,includingtheirradialdensityproﬁle,anditsclaimeduniversality.Onacosmologicalside,high–resolutionN–bodysimulationshaveshownthatcolddarkmatter(CDM)halosachieveaspeciﬁcequilibriumdensityproﬁle[13hereafterNFW,5,8,12,9]characterizedbyonefreeparameter,e.g.thehalomass.IntheinnerregiontheDMhalosdensityproﬁlesshowsomescatteraroundanaverageproﬁlewhichischaracterizedbyapower–lawcuspρ∼r−γ,withγ=1−1.5[13,12,2].Indetail,theDMdensityproﬁleis:ρNFW(r)=ρs2Salucci&BorrielloFig.1.Syntheticrotationcurves(ﬁlledcircleswitherrorbars)andURC(solidline)withtheseparatedark/luminouscontributions(dottedline:disks;dashedline:halos).

assumingtheconcentrationparameterasc≡rvir/rsthehalocircularvelocityVNFW(r)takestheform[2]:

V2NFW(r)=V2vir

x(2)

wherex≡r/rsandA(x)≡ln(1+x)−x/(1+x).AstherelationbetweenVvirandrvirisfullyspeciﬁedbythebackgroundcosmology,theindependentparameterscharacterizingthemodelreducefromthreetotwo(candrs).LetusstressthatahighdensityΩm=1model,withaconcentrationparameterc>12,isdeﬁnitelyunabletoaccountfortheobservedgalaxykinematics[11].Sofar,duetothelimitednumberofsuitableRC’sandtotheseriousun-certaintiesinderivingtheactualamountofluminousmatterinsidetheinnerDarkMatterDistributioninGalaxies3regionsofspirals,ithasbeendiﬃculttoinvestigatetheinternalstructureofdarkhalos.Thesediﬃcultieshavebeenovercomebymeansof:i)aspeciﬁcinvestigationoftheUniversalRotationCurve[16],builtbycoadding1000RC’s,inwhichweadoptageneralhalomassdistribution:

V2h,URC(x)=V2opt(1−β)(1+a2)x2

ropt

;LI4Salucci&BorrielloFig.2.avs.βandβvs.Vopt.andasphericalhalo,whosevelocitycontributionisgivenby(3).Athighlumi-nosities,thecontributionfromabulgecomponenthasalsobeenconsidered.Thedata(i.e.thesyntheticcurvesVsyn)selecttheactualmodeloutofthisfamily,bysettingV2URC(x)=V2h,URC(x,β,a)+V2d,URC(x,β)withaandβasfreeparameters.Anextremelygoodﬁtoccursfora≃1.5(LI/L∗)[16]or,equiv-alently,fora=a(β)andβ=β(logVopt)asplottedinFig.2.WiththesevaluestheURCreproducesthedataVsyn(r)uptotheirrms(i.e.within2%).Moreover,atﬁxedluminositytheσﬁttinguncertaintiesinaandβarelesserthan20%.Theemergingpictureis:i)smallerobjectshavemorefractionalamountofdarkmatter(insideropt:M∗/Mvir≃0.2(M∗/2×1011M⊙)0.75[20]),ii)darkmassincreseswithradiusmuchmorethatlinearly.

2.2HaloDensityProﬁlesTheaboveevidencecallsforaquitespeciﬁcDMdensityproﬁle;weadopttheBBShalomassdistribution[3,4,1]:

ρBBS(r)=ρ0r30DarkMatterDistributioninGalaxies5Fig.3.up)Centralhalodensityρ0(ing/cm3)vs.diskmass(insolarunits)fornormalspirals(ﬁlledcircles);bottom)centraldensityvs.coreradii(inkpc)fornormalspirals.Thestraightlinesarefrom[3],whereasthecurvedlinesarethebestﬁtsusedin§4.

1–parameterfamily,completelyspeciﬁedbye.g.theircoremassM0.Whenwetestthedisk+BBSvelocitieswithρ0andr0leftasfreeparameters,weﬁndthat,atanyluminosityandoutto∼6rd,themodelisindistinguishablefromdata(i.e.Vsyn(r)).Morespeciﬁcally,wereproducethesyntheticrotationcurvesattheleveloftheirrms.Thevaluesofr0andρ0derivedinthiswayagreewiththeextrapolationathighmassesofthescalinglawρ∝r−2/30[3]establishedforobjectswithmuchsmallercoreradiir0andstellarmasses(seeFig.3).Letusnoticethatthecoreradiiareprettylarge(r0≫rd):ever-risinghaloRC’scannotbeexcludedbythedata.Moreover,spiralslieontheextrapolationofthedisk–massvs.centralhalodensityrelationshipρ0∝M−1/3dfoundfordwarfgalaxies[3],toindicatethatthedensesthalosharbortheleastmassivedisks(seeFig.3).