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nova
nova A type of cataclysmic variable that exhibits a sudden, unpredictable outburst, with a typical amplitude of 11–12 mag.; abbr. N. Novae are interacting binaries, and usually consist of a main-sequence or slightly evolved secondary and a white-dwarf primary. Mass transfer occurs from the secondary to an accretion disk and thence to the white dwarf. The accumulation of hydrogen-rich gas on the white dwarf's surface eventually leads to a thermonuclear runaway (a sudden initiation of nuclear reactions), producing the outburst and ejecting much of the outer envelope from the system.
Novae are divided into three subtypes, based on their speed of decline from maximum (see also fast nova): fast (NA), declining by 3 magnitudes in less than 100 days; slow (NB), 3 magnitudes in 150 days or more; very slow (NC), persisting at maximum for years. Very slow novae probably have a giant or supergiant secondary, and are sometimes referred to as symbiotic novae or RR Telescopii stars. No pre-nova has been studied in detail, but there may be a pre-outburst rise of some magnitudes, perhaps with fluctuations and activity like that of a dwarf nova. The initial rise is rapid (less than 1 day in most cases, 2–3 days in slow novae) to a pre-maximum halt, about 2 mag. below maximum. After a few hours to days this is followed by the final rise in 1–2 days or (in slow novae) a few weeks. About 3–4 mag. below maximum, a transition region lasting 2–3 months may occur; some novae undergo a deep fade of 7–10 mag. and a subsequent recovery, while others exhibit quasi-periodic oscillations. The final decline into the post-nova phase is generally steady. The spectrum of a nova at maximum shows a continuum, overlain by a sequence of absorption lines arising in the expanding envelope which indicates velocities of hundreds to thousands of kilometres per second. In the final stages the continuum fades, leaving a nebular spectrum with forbidden lines. There is an extended period of mass loss in which at least 10-4 solar masses is ejected. The mass transfer rate through the accretion disk is estimated at about 10-8 solar masses a year, so the system should undergo a further outburst after about 10 000 years. The ejecta may become visible after a period of time. Estimates suggest that 25 to 50 novae occur each year in our Galaxy, most of which go undetected because of interstellar extinction and other factors. They occur throughout the Galaxy (including the outermost halo) and among systems of all ages from old Population II to extremely young Population I stars. |
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"nova." A Dictionary of Astronomy. 1997. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "nova." A Dictionary of Astronomy. 1997. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O80-nova.html "nova." A Dictionary of Astronomy. 1997. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-nova.html |
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Nova
NovaThe word nova, Latin for "new," was assigned by ancient astronomers to any bright star that suddenly appeared in the sky. A nova occurs when one member of a binary star system temporarily becomes brighter. Most often the brighter star is a shrunken white dwarf, the cooling, shrunken core remaining after a medium-sized star (like our sun) ceases to burn. Its partner is a large star, such as a red giant, a medium-sized star in a late stage of its evolution, expanding and cooling. As the companion star expands, it loses some of its matter—mostly hydrogen—to the strong gravitational pull of the white dwarf. After a time, enough matter collects in a thin, dense, hot layer on the surface of the white dwarf to initiate nuclear fusion reactions. The hydrogen on the white dwarf's surface burns away, and while it does so, the white dwarf glows brightly. This is a nova. After reaching its peak brightness, it slowly fades over a period of days or weeks. The transfer of matter does not stop after a nova explodes, but begins anew. The length of time between nova outbursts can range from several dozen to thousands of years, depending on how fast the companion star loses matter to the white dwarf. A nova should not be confused with a supernova, which is the massive explosion of a relatively large star. A nova is much more common than a supernova, and it does not release nearly as much energy. Because novae (plural of nova) occur more often, they can change the way constellations in the night sky appear. For example, in December 1999, a bright, naked-eye nova appeared in the constellation Aquila, the Eagle. At its maximum, the nova was as bright as many of the stars in Aquila. For a few days at least, viewers were treated to the spectacle of a truly "new star" in an otherwise familiar constellation. Words to KnowBinary star: Pair of stars in a single system that orbit each other, bound together by their mutual gravities. Red giant: A medium-sized star in a late stage of its evolution. It is relatively cool and has a diameter that is perhaps 100 times its original size. White dwarf: The cooling, shrunken core remaining after a medium-sized star ceases to burn. [See also Binary star; Star; Supernova; White dwarf ] |
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"Nova." UXL Encyclopedia of Science. 2002. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "Nova." UXL Encyclopedia of Science. 2002. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1G2-3438100455.html "Nova." UXL Encyclopedia of Science. 2002. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3438100455.html |
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nova
no·va / ˈnōvə/ • n. (pl. -vae / -vē; -ˌvī/ or -vas ) Astron. a star showing a sudden large increase in brightness and then slowly returning to its original state over a few months. See also supernova. |
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"nova." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "nova." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O999-nova.html "nova." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-nova.html |
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nova
nova (pl. novae) Faint star that undergoes unpredictable increases in brightness by several magnitudes, apparently due to explosions in its outer regions, and then slowly fades back to normal. See also variable star
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"nova." World Encyclopedia. 2005. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "nova." World Encyclopedia. 2005. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O142-nova.html "nova." World Encyclopedia. 2005. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-nova.html |
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nova
nova see supernova ; variable star . |
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"nova." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "nova." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1E1-X-nova.html "nova." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-X-nova.html |
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nova
nova A new star.
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AILSA ALLABY and MICHAEL ALLABY. "nova." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "nova." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O13-nova.html AILSA ALLABY and MICHAEL ALLABY. "nova." A Dictionary of Earth Sciences. 1999. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-nova.html |
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nova
nova •aquiver, downriver, forgiver, giver, quiver, river, shiver, sliver, upriver
•silver • mitzvah • lawgiver • Oliver
•miniver, Nineveh
•quicksilver
•conniver, contriver, diver, driver, fiver, Godiva, Ivor, jiver, Liver, reviver, saliva, skiver, striver, survivor, viva
•skydiver • slave-driver • piledriver
•screwdriver
•bovver, hover
•Moskva
•revolver, solver
•windhover
•Canova, Casanova, clover, Dover, drover, Grsbover, Jehovah, left-over, Markova, Moldova, moreover, Navrátilová, nova, ova, over, Pavlova, rover, trover, up-and-over
•layover • flyover • handover
•changeover
•makeover, takeover
•walkover • spillover • pullover
•Hanover • turnover • hangover
•wingover • sleepover • slipover
•popover, stopover
•Passover • crossover • once-over
•pushover • leftover
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Cite this article
"nova." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "nova." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O233-nova.html "nova." Oxford Dictionary of Rhymes. 2007. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O233-nova.html |
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