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Topic: Star formation

	Star formation - Wikipedia, the free encyclopedia
		Star formation is the process by which gas in molecular clouds change into the ball of plasma we call a star.
		In high mass stars, the length of the star formation process is comparable to the other timescales of their evolution, much shorter, and the process is not so well defined.
		The radiation from the protostar and early star has to be observed in infrared astronomy wavelengths, the extinction caused by the rest of the cloud where it is being formed is usually too big to allow us to observe it in the visual part of the spectrum.
	en.wikipedia.org /wiki/Star_formation (449 words)

	Star - Wikipedia, the free encyclopedia
		Scientifically, stars are defined as self-gravitating spheres of plasma in hydrostatic equilibrium, which generate their own energy through the process of nuclear fusion.
		Star formation occurs in molecular clouds, large regions of high density in the interstellar medium (though still less dense than the inside of an earthly vacuum chamber).
		Star formation begins with gravitational instability inside those clouds, often triggered by shockwaves from supernovae or collision of two galaxies (as in a starburst galaxy).
	en.wikipedia.org /wiki/Star (1943 words)

	Kids.net.au - Encyclopedia Star formation - (Site not responding. Last check: 2007-11-07)
		Finally, hydrogen ignites in the core of the star, and the rest of the enveloping material is cleared away.
		The later evolution of the star is studied in stellar evolution.
		The radiation from the protostar and early star have to be observed in the infrared astronomy, the extinction caused by the rest of the cloud where it is being formed is usually too big to allow us to observe in the visual.
	www.kidsseek.com /encyclopedia-wiki/st/Star_formation (285 words)

	Star Formation, Life, and Death
		This was accompanied by the release of energy, which made the star begin to shine and in turn halt the gravitational collapse of the star.
		In other cases, a star's death was slower; instead of an explosion, elements from the star's interior zones rose to the surface and were then lost to space when the outer layers blew off.
		The initial mass of the star is an important factor involved with the life of a star and helps to answer many other questions: how long will the star live, at what temperature will it emit radiation, and at what part of the electromagnetic spectrum will the radiation be emitted.
	www.solarviews.com /eng/starformation.htm (1185 words)

	General Information
		The large and steadily increasing number of papers on star formation that are based on high resolution studies at X-ray, optical, infrared, millimetre, and radio wavelengths testifies to the vigour and timely appeal of this topic.
		Despite its luminosity, which enables a complete census of massive star formation to be undertaken in the galaxy, it is still a poorly understood process.
		Star formation studies in external galaxies allow us to study modes of star formation and physical conditions that can be very different from those found in our own Galaxy.
	www.phys.unsw.edu.au /iau221 (1276 words)

	THE INFRARED UNIVERSE - Star Formation
		Stars form from collapsing clouds of gas and dust.
		As the cloud collapses, its density and temperature increase.
		Both Herbig-Haro objects and T-Tauri stars are found in regions of active star formation.
	www.ipac.caltech.edu /Outreach/Edu/sform.html (673 words)

	Star Formation (Site not responding. Last check: 2007-11-07)
		An understanding of the process of star formation is an essential requirement of theories of galaxy formation and evolution, and gives direct insights into the formation of our own Sun and the number of extra-solar planets we expect to find in the Galaxy.
		In particular, we study the supersonic jets ejected during the star formation process, and the accretion disks surrounding the protostars which allow the stars to grow in mass and in which planets are believed to form.
		Multi-wavelength studies are used to determine the pattern of star formation in the recent past in a variety of galaxy types and relate this to the observed structure and dynamics in the cold ISM.
	www.mrao.cam.ac.uk /research/starform.html (238 words)

	ScienceWeek
		This apparent universality of the IMF is a challenge for star formation theory, because elementary considerations suggest that the IMF ought to systematically vary with star-forming conditions.
		On the northern hemisphere virtually all very-low-mass stars in the immediate neighborhood (93) and all low-mass stars in the neighborhood are known and have accurate distance measurements using trigonometric parallax.
		Star clusters form at all epochs of galactic evolution, are associated with galaxies of all Hubble types, and have similar IMFs, which suggest a common and robust mechanism of star formation.
	scienceweek.com /2003/sw030822.htm (6151 words)

	Star formation Info - Encyclopedia WikiWhat.com (Site not responding. Last check: 2007-11-07)
		In the current paradigm of star formation, cores of molecular clouds (regions of especially high density) become gravitationally unstable, and start to collapse.
		Part of the gravitational energy lost in this collapse is radiated in the infrared, with the remainder increasing the temperature of the core.
		In high mass stars, the length of the star formation process is comparable to the other timescales of their evolution and the process is not so well defined.
	www.wikiwhat.com /encyclopedia/s/st/star_formation_1.html (393 words)

	Lecture 17: Star Formation (Site not responding. Last check: 2007-11-07)
		Since stars don't live forever, then they must be "born" somewhere and at some time in the past.
		Stars form in giant clouds of gas and dust called molecular clouds.
		After a star is born it heats the gas and dust around it.
	instruct1.cit.cornell.edu /courses/astro101/lec17.htm (374 words)

	Stellar Evolution: Main Sequence
		Stars begin their lives as 74% hydrogen, 25% helium and 1% everything else on the periodic table (by mass).
		Assuming that about 1/2 mass of the star is passed through the fusion reaction in the core, which converts 0.71% of the mass of four protons into energy.
		Even though the star is brighter, produces more energy, its pressure has increased such that its surface area has become very large, and the surface temperature of the star drops into the K and M spectral type regions.
	zebu.uoregon.edu /~js/ast122/lectures/lec14.html (1312 words)

	Star Formation
		Young stars also have dark spots on their surfaces which are analogous to sunspots but cover a much larger fraction of the surface area of the star.
		The evolution of young stars is from a cluster of protostars deep in a molecular clouds core, to a cluster of T-Tauri stars whose hot surface and stellar winds heat the surrounding gas to form an HII region (HII, pronounced H-two, means ionized hydrogen).
		Neither planets nor stars, brown dwarfs share properties with both kinds of objects: They are formed in molecular clouds much as stars are, but their atmospheres are reminiscent of the giant gaseous planets.
	zebu.uoregon.edu /~js/ast122/lectures/lec13.html (1574 words)

	Origins: Star Formation (Site not responding. Last check: 2007-11-07)
		Where there were higher concentrations of gases, the mutual gravitational attractions of the gas molecules led to the growth of the first generation of stars.
		As more and more material fell into a new star, the pressure at its center finally became high enough to start the process of nuclear fusion, in which the nuclei of hydrogen and helium merge to form heavier elements.
		In other cases, the process was slower; instead of an explosion, elements from the star's interior zones rose to the surface and were then lost to space when the outer layers blew off.
	origins.stsci.edu /under/stars.shtml (637 words)

	UK Astrophysical Fluids Facility
		The Formation of Stars and Brown Dwarfs and the Truncation of Protoplanetary Discs in a Star Cluster
		Some stars and brown dwarfs have been ejected to large distances from the regions of dense gas in which the star formation occurs.
		The stars and discs in the main star-forming region at the end of the calculation.
	www.ukaff.ac.uk /starcluster (881 words)

	Nebulae and Star Formation
		The proplyds which are closest to the hottest stars of the parent star cluster are seen as bright objects, while the object farthest from the hottest stars is seen as a dark object.
		The massive stars in A1 and A2 must have formed within the last 10,000 years, since their natal gas shrouds are not yet disrupted by the powerful radiation of the newly born stars.
		But once these luminous stars began to irradiate and destroy their surroundings, the clumps became visible when their less dense surroundings were eroded away, thus exposing them to the full brunt of the ultraviolet radiation and the expanding HII region.
	faculty.rmwc.edu /tmichalik/NebandStar.htm (6462 words)

	Star formation (Site not responding. Last check: 2007-11-07)
		Stars are born in dense regions inside giant molecular clouds (GMCs), which are clouds of hydrogen gas and dust between stars.
		A protostar is not as hot and bright as an ordinary star, and it is cocooned in the gas and dust that are still falling onto the spinning disk.
		The molecular clouds in Orion are observed to be regions of prolific star formation.
	www.physics.usyd.edu.au /rcfta/anrep93/node19.html (905 words)

	Colliding galaxies provide clues to star formation in early universe
		“Studying galaxy interactions is crucial to understanding the large-scale star formation that occurred when the universe was young — about one third of its present age — when it is thought that star formation was at its height,” said Susan Lamb, a UI professor of physics and of astronomy.
		To investigate the sequence of star formation triggered by a galaxy collision, Lamb and graduate student Nathan Hearn used a three-dimensional numerical simulation of a collision between a gas-rich disk galaxy and a gas-free elliptical galaxy.
		Such episodic star formation could be due to gravitational or hydrodynamic instabilities in the disturbed gas, and may be indicative of processes that occurred on a grand scale in the early universe.
	www.eurekalert.org /pub_releases/2001-04/UoIa-Cgpc-3004101.php (426 words)

	Star Formation (Site not responding. Last check: 2007-11-07)
		Studies of the impact of star formation via stellar winds and supernovae {'feedback'} on the properties of a galaxy are of fundamental importance to...
		These nebulae are areas of intense star formation within giant molecular hydrogen clouds.
		In this stage bipolar flows are produced, probably a effect of the angular momentum of the falling material.
	www.wikiverse.org /star-formation (467 words)

	[52.17] Star Formation Rate History of the Local Universe (Site not responding. Last check: 2007-11-07)
		The former model describes spheroidal galaxy formation as occurring in one large initial burst of star formation, followed by passive galaxy evolution, as the stars slowly age.
		The star formation rate density as a function of redshift can distinguish between these two models by showing us when most of the stars in the universe were made.
		All studies indicate a steep increase in the star formation rate from z = 0 to z = 1, although the magnitude of this jump remains in question.
	www.aas.org /publications/baas/v34n4/aas201/186.htm (341 words)

	Report of the Star Formation and Stellar Evolution Working Group
		One of the most fundamental goals in the field of star formation is the measurement of the motions associated with gravitational infall leading to star formation.
		Theories for the formation of the Jovian and terrestrial planets depend critically on the dissipation timescale of the gas in the disk, and the coagulation timescale of the dust grains.
		At greater distances from the star, the distribution of organic molecules, radicals, and ions is determined by the photo-chemical processes which occur in outer envelopes of cool evolved stars.
	www.alma.nrao.edu /science/starformation/starform.html (3156 words)

	Star Formation
		Star formation by this route is physically impossible.
		Astronomers like Bok, Cameron and Spitzer recognize that stars are not going to form by simple gravitational contraction, but that they require some sort of outside influence, like shock waves from the explosion of a star, to push the cloud to greater density to satisfy the requirements described by Sir Jeans and others.
		Although gravitational formation of stars is conceivable, it is not possible.
	www.ldolphin.org /stars.html (3103 words)

	Universe Today - Adaptive Optics Reveal Massive Star Formation
		The young massive stars that the team observed are usually too blurry when seen from the ground, so they made the perfect target for the adaptive optics system.
		Herbig Ae/Be stars, with masses between 1.5 and 10 times that of the sun and probably less than 10 million years old, are thought to be the beginnings of massive stars - stars that will end up like the hot, Type A stars Sirius and Vega.
		Interestingly, a third star imaged the same night by Graham and Perrin turned out to be two sun-like stars with a ribbon of gas and dust between them, looking suspiciously like one star capturing matter from the other.
	www.universetoday.com /am/publish/adaptive_optics_star_formation.html?332004 (1628 words)

	Imperial College London - New vision of star formation (Site not responding. Last check: 2007-11-07)
		Their observations suggest that there was much earlier star formation in the universe than astronomers studying visible light have detected.
		It was previously thought that the peak of star formation occurred when the universe was about half its present age.
		However, the group have now found evidence of early star formation, when the Universe was roughly one-eighth of its present age, at rates up to five times higher than those previously interpreted from optical and ultraviolet studies.
	www.ic.ac.uk /P1816.htm (522 words)

	High-mass X-ray Binaries as a Star Formation Rate Indicator
		We call star fomration rate the mass of gas and dust that is converted into stars per year.
		These double star systems are consist of a massive star, at least 10 times more massive than the Sun, and a so-called compact object, a neutron star or fl hole.
		These particular double star systems are well suited to measure the star formation rate since their lifetime is very short: The more massive a star is the shorter it lives.
	www.mpa-garching.mpg.de /new-home/HIGHLIGHT/2003/highlight0307_e.html (808 words)

	Spaceflight Now \| Breaking News \| Galaxy shows key evidence for furious star formation
		Astronomers have discovered a key signpost of rapid star formation in a galaxy 11 billion light-years from Earth, seen as it was when the Universe was only 20 percent of its current age.
		While the raw material for star formation has been found in galaxies at even greater distances, the Cloverleaf is by far the most distant galaxy showing this essential signature of star formation.
		The rapid star formation, called a starburst, and the fl hole are both generating the bright infrared light in the Cloverleaf.
	www.spaceflightnow.com /news/n0312/10cloverleaf (987 words)

	CSFS HOME PAGE (Site not responding. Last check: 2007-11-07)
		The Center for Star Formation Studies is a consortium of researchers working together in a coordinated fashion to construct a comprehensive theoretical model of the process of star formation.
		In the past, workshops have been held at Wellesley College (with the collaboration of the star formation group at the Smithsonian Astrophsyical Obsevrtory), in Taiwan and in Italy.
		The CSFS is part of NASA's overall program to study the origin of stars and planets and to ultimately understand how life arises in the Universe.
	web99.arc.nasa.gov /~csf/index.html (452 words)

	Accretion Disk Polar Jetting, Binary Star Formation and Nemesis
		Consequently, orbits are longer lived as their planes approach a right angle to that of the accretion disk and/or the eccentricity of the elliptical orbit increases.
		Near the core of the forming star in the accretion disk an eye exists where dropping particles are sufficient in number to hamper close orbits.
		It varies in size, shape, and orbital plane throughout star formation as dictated by dust particles within its influence.
	www.aplg.com /nemesis.htm (996 words)

	ESA Portal - Focus On - Hubble studies generations of star formation in neighbouring galaxy
		The NASA/ESA Hubble Space Telescope captures the iridescent tapestry of star birth in a neighbouring galaxy in this panoramic view of glowing gas, dark dust clouds, and young, hot stars.
		With its high resolution, the Hubble Space Telescope is able to view details of star formation in the LMC as easily as ground-based telescopes are able to observe stellar formation within our own Milky Way galaxy.
		It is a subregion within a larger area of star formation called N11.
	www.esa.int /esaCP/SEMO3Y4W4WD_FeatureWeek_1.html (500 words)

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