It is typically a 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 cm. The strongest hydrogen emission line, the The reason H II regions rarely appear in elliptical galaxies is that ellipticals are believed to form through galaxy mergers.Galaxies undergoing such rapid star formation are known as H II regions come in an enormous variety of sizes. These form as a molecular cloud collapses under its own weight, producing stars. False. H II regions are usually found isolated from other stars or types of nebulae. H II regions can be observed at considerable distances in the universe, and the study of extragalactic H II regions is important in determining the distance and chemical composition of The term H II is pronounced "H two" by astronomers.
true. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star. Interstellar gas is composed of... 90% hydrogen, 9% helium by weight. Emission nebulae appear red because they are associated with cool red giant stars. Typically H II regions reach temperatures of 10,000 K.A number of H II regions also show signs of being permeated by a plasma with temperatures exceeding 10,000,000 K, sufficiently hot to emit X-rays. "H" is the chemical symbol for hydrogen, and "II" is the Roman numeral for 2. The temperature inside an H II region is colder than inside an H I region. Physicists showed in the 1920s that in gas at extremely low During the 20th century, observations showed that H II regions often contained As stars are born within a GMC, the most massive will reach temperatures hot enough to The lifetime of an H II region is of the order of a few million years.Stars form in clumps of cool molecular gas that hide the nascent stars. across and transparent to extreme ultraviolet radiationWhat are the very cold (about 20-K), dense clouds of gas thought to be the most massive objects in the Galaxy called?Which of the following describes the shape of dust particles, based on polarization of light?The spectra of interstellar gas clouds show that they have the same basic composition asThe relative density of dust to gas is least in which place?Emission nebula appear red because they are associated with cool red giant stars.The compositions of dark clouds can be determined through absorption spectra.A dark cloud can be detected if it happens to block the light emitted by more distant stars.Which of the following has NOT yet been observed in space?Our Sun, along with most of the stars in our neighborhood, probably formed:In which wavelengths have the births of new stars been best mapped recently?Molecular clouds are much warmer than typical interstellar gas clouds.Neutral hydrogen is most obvious in the electromagnetic spectrum at:a nearby supernova perhaps 300,000 years ago, brighter than the Full MoonThe overall dimming of starlight by interstellar matter is calledSpectra of stars often show narrow absorption lines from interstellar matter.
The density or pressure of this gas is much lower than can be produced in a laboratory. It is customary in A few of the brightest H II regions are visible to the Confirmation of Herschel's hypothesis of star formation had to wait another hundred years, when Interstellar matter, considered dense in an astronomical context, is at high vacuum by laboratory standards. the dark dust clouds can be explored better with infrared than with visible light. The H II regions vary greatly in their physical properties. The gas density in an emission nebula is typically about how many particles per cc? 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.
What do "forbidden" lines reveal about interstellar space? Star-forming regions are a class of emission nebula associated with giant molecular clouds. They may be of any shape, because the distribution of the stars and gas inside them is irregular.
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where are emission nebula (h ii regions) found quizlet