Spider & the Web. Space. Beyond space and time: Fractals, hyperspace and more. Universe. There are many competing theories about the ultimate fate of the universe. Physicists remain unsure about what, if anything, preceded the Big Bang. Many refuse to speculate, doubting that any information from any such prior state could ever be accessible.
There are various multiverse hypotheses, in which some physicists have suggested that the Universe might be one among many or even an infinite number of universes that likewise exist.[11][12] Historical observation XDF size compared to the size of the Moon – several thousand galaxies, each consisting of billions of stars, are in this small view. XDF (2012) view – each light speck is a galaxy – some of these are as old as 13.2 billion years[13] – the visible Universe is estimated to contain 200 billion galaxies. XDF image shows fully mature galaxies in the foreground plane – nearly mature galaxies from 5 to 9 billion years ago – protogalaxies, blazing with young stars, beyond 9 billion years. History Etymology, synonyms and definitions. Black hole.
A black hole is defined as a region of spacetime from which gravity prevents anything, including light, from escaping.[1] The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole.[2] Around a black hole, there is a mathematically defined surface called an event horizon that marks the point of no return. The hole is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics.[3][4] Quantum field theory in curved spacetime predicts that event horizons emit radiation like a black body with a finite temperature.
This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater. Objects whose gravity fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. History General relativity.
Observable Universe. The surface of last scattering is the collection of points in space at the exact distance that photons from the time of photon decoupling just reach us today. These are the photons we detect today as cosmic microwave background radiation (CMBR). However, with future technology, it may be possible to observe the still older neutrino background, or even more distant events via gravitational waves (which also should move at the speed of light). Sometimes astrophysicists distinguish between the visible universe, which includes only signals emitted since recombination—and the observable universe, which includes signals since the beginning of the cosmological expansion (the Big Bang in traditional cosmology, the end of the inflationary epoch in modern cosmology).
The universe versus the observable universe[edit] If the universe is finite but unbounded, it is also possible that the universe is smaller than the observable universe. Size[edit] Misconceptions[edit] 13.8 billion light-years. Galaxy. Galaxies contain varying numbers of planets, star systems, star clusters and types of interstellar clouds. In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays. Supermassive black holes reside at the center of most galaxies. They are thought to be the primary driver of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy is known to harbor at least one such object.[5] Galaxies have been historically categorized according to their apparent shape, usually referred to as their visual morphology.
Etymology[edit] The word galaxy derives from the Greek term for our own galaxy, galaxias (γαλαξίας, "milky one"), or kyklos ("circle") galaktikos ("milky")[11] for its appearance as a lighter colored band in the sky. In the astronomical literature, the capitalized word 'Galaxy' is used to refer to our galaxy, the Milky Way, to distinguish it from the billions of other galaxies. Nomenclature[edit] Observation history[edit] Milky Way[edit] Nebula. Portion of the Carina nebula A nebula (from Latin: "cloud";[1] pl. nebulae or nebulæ, with ligature, or nebulas) is an interstellar cloud of dust, hydrogen, helium and other ionized gases.
Originally, nebula was a name for any diffuse astronomical object, including galaxies beyond the Milky Way. The Andromeda Galaxy, for instance, was referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others. Nebulae are often star-forming regions, such as in the Eagle Nebula. Observational history The "Pillars of Creation" from the Eagle Nebula. On November 26, 1610, Nicolas-Claude Fabri de Peiresc discovered the Orion Nebula using a telescope. In 1715, Edmund Halley published a list of six nebulae.[8] This number steadily increased during the century, with Jean-Philippe de Cheseaux compiling a list of 20 (including eight not previously known) in 1746.
Spiral Galaxy. An example of a spiral galaxy, the Pinwheel Galaxy (also known as Messier 101 or NGC 5457) Spiral galaxies are named for the spiral structures that extend from the center into the disk. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disk because of the young, hot OB stars that inhabit them. Roughly two-thirds of all spirals are observed to have an additional component in the form of a bar-like structure,[2] extending from the central bulge, at the ends of which the spiral arms begin. The proportion of barred spirals relative to their barless cousins has changed over the history of the Universe, with only about 10% containing bars about 8 billion years ago, roughly a quarter 2.5 billion years ago, till now at over two-thirds.[3] Together with irregular galaxies, spiral galaxies make up approximately 60% of galaxies in the local Universe.[6] They are mostly found in low-density regions and are rare in the centers of galaxy clusters.[7] Other.
Virgo. The Virgo Supercluster (Virgo SC) or Local Supercluster (LSC or LS) is the irregular supercluster that contains the Virgo Cluster in addition to the Local Group, which in turn contains the Milky Way and Andromeda galaxies. At least 100 galaxy groups and clusters are located within its diameter of 33 megaparsecs (110 million light-years). It is one of millions of superclusters in the observable universe.
Background[edit] Beginning with the first large sample of nebulae published by William and John Herschel in 1863, it was known that there is a marked excess of nebular fields in the constellation Virgo (near the north galactic pole). In the 1950s, French–American astronomer Gérard Henri de Vaucouleurs was the first to argue that this excess represented a large-scale galaxy-like structure, coining the term "Local Supergalaxy" in 1953 which he changed to "Local Supercluster" (LSC[2]) in 1958. Structure[edit] Galaxy distribution[edit] Cosmology[edit] Large scale dynamics[edit] Dark matter[edit]
Galaxies Gone Wild. Star. For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and then radiates into outer space. Once the hydrogen in the core of a star is nearly exhausted, almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star's lifetime and, for some stars, by supernova nucleosynthesis when it explodes. Near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity (chemical composition), and many other properties of a star by observing its motion through space, luminosity, and spectrum respectively.
The total mass of a star is the principal determinant of its evolution and eventual fate. Other characteristics of a star, including diameter and temperature, change over its life, while the star's environment affects its rotation and movement. Observation history. Supernova. A supernova (abbreviated SN, plural SNe after "supernovae") is a stellar explosion that is more energetic than a nova. It is pronounced /ˌsuːpəˈnoʊvə/ with the plural supernovae /ˌsuːpəˈnoʊviː/ or supernovas.
Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. During this interval a supernova can radiate as much energy as the Sun is expected to emit over its entire life span.[1] The explosion expels much or all of a star's material[2] at a velocity of up to 30,000 km/s (10% of the speed of light), driving a shock wave[3] into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant.
Nova means "new" in Latin, referring to what appears to be a very bright new star shining in the celestial sphere; the prefix "super-" distinguishes supernovae from ordinary novae which are far less luminous. Discovery[edit] First Organic Molecule on Extrasolar. Technology Review: The Authority on the Future of Technology.
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