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The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to occur from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. The simplest model in general agreement with observed phenomena is the Lambda-CDM model—that is, that clustering and merging allows galaxies to accumulate mass, determining both their shape and structure. Hydrodynamics simulation, which simulates both baryons and dark matter, is widely used to study galaxy formation and evolution.
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a hundred million stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies.
A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, H2), and the formation of H II regions. This is in contrast to other areas of the interstellar medium that contain predominantly ionized gas.
Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or "star-forming regions", collapse and form stars. As a branch of astronomy, star formation includes the study of the interstellar medium (ISM) and giant molecular clouds (GMC) as precursors to the star formation process, and the study of protostars and young stellar objects as its immediate products. It is closely related to planet formation, another branch of astronomy. Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function. Most stars do not form in isolation but as part of a group of stars referred as star clusters or stellar associations.
Galactic astronomy is the study of the Milky Way galaxy and all its contents. This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies.
Astronomy is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole.
In astronomy, the interstellar medium (ISM) is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy that occupies the same volume, in the form of electromagnetic radiation, is the interstellar radiation field. Although the density of atoms in the ISM is usually far below that in the best laboratory vacuums, the mean free path between collisions is short compared to typical interstellar lengths, so on these scales the ISM behaves as a gas (more precisely, as a plasma: it is everywhere at least slightly ionized), responding to pressure forces, and not as a collection of non-interacting particles.
An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light years, and density from a few to about a million particles per cubic centimetre. The Orion Nebula, now known to be an H II region, was observed in 1610 by Nicolas-Claude Fabri de Peiresc by telescope, the first such object discovered.
The Zone of Avoidance, or Zone of Galactic Obscuration (ZGO), is the area of the sky that is obscured by the Milky Way.
Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. There are several schemes in use by which galaxies can be classified according to their morphologies, the most famous being the Hubble sequence, devised by Edwin Hubble and later expanded by Gérard de Vaucouleurs and Allan Sandage. However, galaxy classification and morphology are now largely done using computational methods and physical morphology.
A megamaser is a type of astrophysical maser, which is a naturally occurring source of stimulated spectral line emission. Megamasers are distinguished from other astrophysical masers by their large isotropic luminosity. Megamasers have typical luminosities of 103 solar luminosities (L☉), which is 100 million times brighter than masers in the Milky Way, hence the prefix mega. Likewise, the term kilomaser is used to describe masers outside the Milky Way that have luminosities of order L☉, or thousands of times stronger than the average maser in the Milky Way, gigamaser is used to describe masers billions of times stronger than the average maser in the Milky Way, and extragalactic maser encompasses all masers found outside the Milky Way. Most known extragalactic masers are megamasers, and the majority of megamasers are hydroxyl (OH) megamasers, meaning the spectral line being amplified is one due to a transition in the hydroxyl molecule. There are known megamasers for three other molecules: water (H2O), formaldehyde (H2CO), and methine (CH).
The Gould Belt is a local ring of stars in the Milky Way, tilted away from the galactic plane by about 16–20 degrees, first reported by John Herschel and Benjamin Gould in the 19th century. It contains many O- and B-type stars, and many of the nearest star-forming regions of the local Orion Arm, to which the Sun belongs. The relative proximity of these star-forming regions spurred the Gould Belt Survey project to determine what caused them.
The Cosmic Origins Spectrograph (COS) is a science instrument that was installed on the Hubble Space Telescope during Servicing Mission 4 (STS-125) in May 2009. It is designed for ultraviolet (90–320 nm) spectroscopy of faint point sources with a resolving power of ≈1,550–24,000. Science goals include the study of the origins of large scale structure in the universe, the formation and evolution of galaxies, and the origin of stellar and planetary systems and the cold interstellar medium. COS was developed and built by the Center for Astrophysics and Space Astronomy (CASA-ARL) at the University of Colorado at Boulder and the Ball Aerospace and Technologies Corporation in Boulder, Colorado.
Sagittarius B2 is a giant molecular cloud of gas and dust that is located about 120 parsecs (390 ly) from the center of the Milky Way. This complex is the largest molecular cloud in the vicinity of the core and one of the largest in the galaxy, spanning a region about 45 parsecs (150 ly) across. The total mass of Sgr B2 is about 3 million times the mass of the Sun. The mean hydrogen density within the cloud is 3000 atoms per cm3, which is about 20–40 times denser than a typical molecular cloud.
Christopher David Impey is a British astronomer, educator, and author. He has been a faculty member at the University of Arizona since 1986. Impey has done research on observational cosmology, in particular low surface brightness galaxies, the intergalactic medium, and surveys of active galaxies and quasars. As an educator, he has pioneered the use of instructional technology for teaching science to undergraduate non-science majors. He has written many technical articles and a series of popular science books including The Living Cosmos, How It Began, How It Ends: From You to the Universe, Dreams of Other Worlds, and Humble Before the Void. He served as Vice-President of the American Astronomical Society, he is a Fellow of the American Association for the Advancement of Science, and a Howard Hughes Medical Institute Professor. He serves on the Advisory Council of METI.
Alice Eve Shapley is a professor at the University of California, Los Angeles (UCLA) in the Department of Physics and Astronomy. She was one of the discoverers of the spiral galaxy BX442. Through her time at University of California, Los Angeles (UCLA) she has taught Nature of the Universe, Black Holes and Cosmic Catastrophes, Cosmology: Our Changing Concepts of the Universe, Galaxies, Scientific Writing, AGNs, Galaxies, *and* Writing, and The Formation and Evolution of Galaxies and the IGM. Shapley has committed herself too over a two decades of research and publication in the interest of physics and astronomy.
Judith Sharn Young was an American physicist, astronomer, and educator. The American Physical Society honored Young with the first Maria Goeppert-Mayer Award for being the best young physicist in the world in 1986. Astronomer Nick Scoville of Caltech writes of her research: "Her pioneering galactic structure research included some of the earliest mapping of CO emission in galaxies followed by the most extensive surveys molecular gas and star formation in nearby galaxies."
The following outline is provided as an overview of and topical guide to galaxies:
Peter Lawrence Capak is currently the Architect of Perception Systems at the Oculus division of Facebook. His current focus is developing machine perception technologies, sensors, displays, and compute architectures for the next generation of augmented (AR), mixed (MR) and virtual reality (VR) systems. His research has focused on using physical modeling and advanced statistical methods including artificial intelligence and machine learning to extract information from very large multi-wavelength (hyper-spectral) data sets. He has primarily used this to study structure formation in the universe, cosmology, and the nature of dark matter and dark energy.
References
- 1 2 Scoville, N.; Aussel, H.; Brusa, M.; Capak, P.; Carollo, C. M.; Elvis, M.; Giavalisco, M.; Guzzo, L.; Hasinger, G.; Impey, C.; Kneib, J. ‐P.; Lefevre, O.; Lilly, S. J.; Mobasher, B.; Renzini, A.; Rich, R. M.; Sanders, D. B.; Schinnerer, E.; Schminovich, D.; Shopbell, P.; Taniguchi, Y.; Tyson, N. D. (2007). "The Cosmic Evolution Survey (COSMOS): Overview". The Astrophysical Journal Supplement Series. 172 (1): 1–8. arXiv: astro-ph/0612305 . Bibcode:2007ApJS..172....1S. doi:10.1086/516585. S2CID 34251129.
- ↑ John Simon Guggenheim Foundation | Nicholas Z. Scoville
- ↑ 2015 Jansky Lecture: Dr. Nick Scoville — Science Website
- 1 2 "The Bruce Medalists". The Bruce Medalists. Astronomical Society of the Pacific. Retrieved 28 November 2020.
- ↑ "Nick Z. Scoville". Caltech. Retrieved 2008-12-23.
- ↑ "Nicholas Z. (Nick) Scoville | Caltech Directory". directory.caltech.edu. Retrieved 2022-06-05.
- ↑ "Columbia Spectator 3 March 1969 — Columbia Spectator". spectatorarchive.library.columbia.edu. Retrieved 2022-06-05.
- ↑ Keto, Eric. "Eric Keto's MIR Website". Senter for Astrophysics. Retrieved 28 November 2020.
- ↑ "JPL Small-Body Database Browser". Jet Propulsion Laboratory. Retrieved November 28, 2020.
- ↑ "Henry Norris Russell Lectureship". American Astronomical Society. Retrieved 25 April 2021.
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