What, When, Where, How and Who

The Evolution of Galaxies

Introduction, Important Definitions and Related Concepts

The process to restore the far-ultraviolet detector on the Galaxy Evolution Explorer has been successfully completed, and the instrument resumed full, normal operations on December 17. Stars are the fundamental building blocks of galaxies. The formation of galaxies is still one of the most active research areas in astrophysics; this is also true for galaxy evolution. Galaxies are large systems of stars and interstellar matter, typically containing several million to some trillion stars, of masses between several million and several trillion times that of our Sun, of an extension of a few thousands to several 100,000s light years, typically separated by millions of light years distance. Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as stars, galaxies, and the interstellar medium, as well as their interactions. Astronomy is the scientific study of celestial objects (such as stars, planets, comets, and galaxies) and phenomena that originate outside the Earth's atmosphere (such as the cosmic background radiation). Physics is the science of matter^{a title="" href="#_note-0">[1]} and its motion,^{a title="" href="#_note-1">[2]/sup>sup> as well as space and timesup> �?? the science that deals with concepts such as force, energy, mass, and charge. The Universe is most commonly defined as everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. In astronomy, luminosity is the amount of energy a body radiates per unit time. In physics, density is mass (m) per unit volume (V) �?? the ratio of the amount of matter in an object compared to its volume. Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. A chemical substance is a material with a definite chemical composition. The term celestial refers to the sky and/or Heaven. The modest American College Dictionary, for example, contains some twelve entries for the term object, among which appear the following: �??something that may be perceived by the senses, especially by sight or touch�??, and again, �??anything that may be presented to the mind: objects of thought.�?? In astronomy, the interstellar medium (or ISM) is the gas and dust that pervade interstellar space: the matter that exists between the stars within a galaxy.  Medium is Something, such as an intermediate course of action, that occupies a position or represents a condition midway between extremes. Science (from the Latin scientia, 'knowledge'), in a historical sense, refers to any systematic knowledge or practice.Studying, The pursuit of knowledge, as by reading, observation, or research. A star is a massive, luminous ball of plasma. A planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.Comets are loose collections of ice, dust, and small rocky particles in the Solar System that orbit the Sun and, when close enough to the Sun, exhibits a visible coma (or atmosphere) and/or a tail �?? both primarily from the effects of solar radiation upon the comet's nucleus. In physics phenomena are the subject of all observation. Earth (pronounced /�?�?rθ/) is the third planet from the Sun and is the largest of the terrestrial planets in the Solar System, in both diameter and mass. The Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. Cosmic means of or relating to the regions of the universe distinct from the Earth. Background means the ground or scenery located behind something. Radiation, as used in physics, is energy in the form of waves or moving subatomic particles. In science, matter is commonly defined as the substance of which physical objects are composed, not counting the contribution of various energy or force-fields, which are not usually considered to be matter per se (though they may contribute to the mass of objects). Motion (physics), any physical movement or change in position or place. Science considers space to be a fundamental quantity (a quantity which can not be defined via other quantities because other quantities �?? like force and energy �?? are already defined via space). Time is a basic component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects. In physics, force is what causes a mass to accelerate. In physics and other sciences, energy (from the Greek ενε�?γ�?�?, energos, "active, working")sup> is a scalar physical quantity that is a property of objects and systems which is conserved by nature. The effect of motion is called momentum. Physical is the the nature (physicality) of a physical entity. Lawsup> is a system of rules usually enforced through a set of institutions.Constants are real numbers or numerical values which are significantly interesting in some waysup>. The volume of a solid object is the three-dimensional concept of how much space it occupies, often quantified numerically. System (from Latin syst�?ma, in turn from Greek �?�?�?�?ημα syst�?ma) is a set of interacting or interdependent entities, real or abstract, forming an integrated whole. Composition (logical fallacy), a fallacy of ambiguation in which one assumes that a whole has a property solely because its various parts have that property. Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape and without a definite volume. Dust is a general name for minute solid particles with diameters less than 500 micrometers. Knowledge is defined (Oxford English Dictionary) variously as (i) expertise, and skills acquired by a person through experience or education; the theoretical or practical understanding of a subject, (ii) what is known in a particular field or in total; facts and information or (iii) awareness or familiarity gained by experience of a fact or situation. Most commonly, practice is a learning method, the act of rehearsing a behavior over and over, or engaging in an activity again and again, for the purpose of improving or mastering it, as in the phrase "practice makes perfect". In physics and chemistry, a plasma is typically an ionized gas. A definition is a statement of the meaning of a word or phrase. International or internationally most often describes interaction between nations, or encompassing two or more nations, constituting a group or association having members in two or more nations, or generally reaching beyond national boundaries. Union generally refers to two or more things joined into one, such as an organization of multiple people or organizations, multiple objects combined into one, and so on. In physics, an orbit is the path that an object makes around another object while under the influence of a central force, such as gravity. A supernova remnant (SNR) is the structure resulting from the gigantic explosion of a star in a supernova. Gravitation is a natural phenomenon and one of the fundamental forces by which all objects with mass attract each other. In physics and nuclear chemistry, nuclear fusion is the process by which multiple atomic particles join together to form a heavier nucleus. Clear Means free from clouds, mist, or haze: a clear day. Neighbour - a nearby object of the same kind; "Fort Worth is a neighbor of Dallas"; "what is the closest neighbor to the Earth?" In general, a region is a medium-scale area of land or water, smaller than the whole areas of interest (which could be, for example, the world, a nation, a river basin, mountain range, and so on), and larger than a specific site or location. Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks. Solar means of, relating to, or proceeding from the sun: solar rays; solar physics. The Sun (Latin: Sol) is the star at the center of the Solar System. Coma (cometary), part of a comet, produced by vapor boiled off the the head of a comet as it nears the sun. Nucleus means a central or essential part around which other parts are gathered or grouped; a core: the nucleus of a city. Pronounce means to enunciate or articulate (sounds, words, sentences, etc.). Terrestrial planet, a planet that is primarily composed of silicate rocks. In geometry, a diameter (Greek words dia = through and metro = measure) of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. Mass is a fundamental concept in physics, roughly corresponding to the intuitive idea of "how much matter there is in an object". A wave is a disturbance that propagates through space and time, usually with transferrance of energy. A subatomic particle is an elementary or composite particle smaller than an atom.}

• Elementary particle, a particle of which larger particles are composed, also called a fundamental particle. Composite particle, a bound state between several elementary particles. Point particle, an idealized particle that does not have any volume. Chemical substance, in chemistry, are material objects that can undergo various transformations related to artificial or natural phenomena. In physics, a force field is a way to picture the effects that electric charges have on one another. Fundamental means 1 a: serving as an original or generating source : primary <a discovery fundamental to modern computers> b: serving as a basis supporting existence or determining essential structure or function : basic2 a: of or relating to essential structure, function, or facts : radical <fundamental change>; also : of or dealing with general principles rather than practical application <fundamental science> b: adhering to fundamentalism3: of, relating to, or produced by the lowest component of a complex vibration4: of central importance : principal <fundamental purpose>5: belonging to one's innate or ingrained characteristics : deep-rooted <her fundamental good humor>.  Quantity is a kind of property which exists as magnitude or multitude. In physics, acceleration is said as the rate of change of velocity, or, the same , as the second derivative of position (with respect to time). Greek (ελληνική γλ�?�?�?α IPA: [elini�?kʲi �?ɣlosa] or simply ελληνικά IPA: [elini�?ka] �?? "Hellenic") has a documented history of 3,400 years, the longest of any single natural language in the Indo-European language family. A scalar is a variable that only has magnitude, e.g. a speed of 40 km/h. An entity is something that has a distinct, separate existence, though it need not be a material existence. Logic (from Classical Greek λ�?γο�? logos; meaning word, thought, idea, argument, account, reason, or principle) is the study of the principles and criteria of valid inference and demonstration. A fallacy is a component of an argument which, being demonstrably flawed in its logic or form, renders the argument invalid in whole. State is a condition or mode of being, as with regard to circumstances: a state of confusion. An atom (Greek �?�?ομο�? or átomos meaning "the smallest indivisible particle of matter, i.e., something that cannot be divided") is the smallest particle characterizing a chemical element. In chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two atoms in a definite arrangement held together by strong chemical bonds. ^{A solid object is in the states of matter characterized by resistance to deformation and changes of volume. A micrometre (American spelling: micrometer; symbol µm) is one millionth of a metre, or equivalently one thousandth of a millimetre. The University of Oxford is one of the leading universities in the world. English is a West Germanic language originating mainly in England, and is the first language for most people in Australia, Canada, the Commonwealth Caribbean, Ireland, New Zealand, the United Kingdom and the United States of America (sometimes referred to as the Anglosphere). Experience as a general concept comprises knowledge of or skill in or observation of some thing or some event gained through involvement in or exposure to that thing or event. E}